Annual Report 5

Projects No 4, 14, 16, 17, 26 and 29 are financially supported in part by the Bulgarian National Science Fund of the Ministry of Education and Science; No8 – by the Ministry of Environment and Waters.

INTRODUCTION

This annual report presents the research activities of the Central Laboratory of Mineralogy and Crystallography during the fifth year of its existence.

The topics developed were in accordance with the preliminary specified scientific and applied priorities. The most significant results, published or reported at conferences, can be grouped as follows:

The studies of natural mineral systems of different rank made it possible to: clarifying the phase composition of platinum group minerals in sediments of the Kustendil graben and in terraces along the Iskar river valley southern of Sofia; identification of rare mineral associations in ultrabasites from Eastern Rhodopes; establishment of Ni-Co-Fe-sulphoarsenides in the Zvezdel-Pcheloyad ore field; determination of the composition and temperature of homogenization of fluid inclusions in barite of different ore-types in Kremikovtsi deposit; definition of relationships in the distribution of rare earth elements in fluorite from the main Bulgarian deposits; establishment of oriented intergrowths between hydrotungstite and ferritungstite from tungsten deposits; morpho- and oregenetic typization of Fe-Mn nodules in the Clarion-Clipperton zone of the Pacific ocean; characterization of the contents, form of presence and the sources of Cl and Br in coal from 34 Bulgarian and world deposits, as well as their behaviour in the waste products of 11 Bulgarian TPS; identification of the phase and mineral composition of six types lignitic, subbituminous and bituminous coal from Bulgarian deposits, oxidized and fired up to 1600° C.
Experimental studies were directed to synthesis of new materials and to modeling of mineral systems: new ionexchange forms of microporous titanosilicates were synthesized and their properties studied as well as the process of crystallization of zeolite-based nanosized particles and thin films; the most suitable solvents for growing of NdAl₃(BO₃)₄ laser crystals are determined; synthesized and structurally solved are new adducts of inorganic compounds and urea, thiourea and their derivatives, which are suitable of growing nonlinear crystals; proposed and experimentally verified is the hypothesis that in the presence of thermal electrodriving forces in magmatic chambers the ion mass-transport can play an important role in the process of homogeneous differentiation of basaltic magma; it is observed experimentally that under temperatures and pressures, typical of processes into the earth crust, silicon is in the form of ortho- and pyro-silicic acid in the equilibrium quartz-water solutions, while its high concentration ion forms do not exist.
Developed are: a model for describing optical spectra of defect multicomponent materials based on their electron and vibration states; a structural model of deformed Al₁₃ - pillars in the interlayer space of natural montmorillonite in order to use it as sorbent and ion exchanger; a structural model of W-Fe oxide fiber microcrystals formed in decomposition of scheelite under hypergenetic conditions; structural models of inhomogeneous tourmalines; a mathematical algorithm for presentation of arbitrary chemical reactions;

Among the most important achievements of practical character are:

Conditions for phase formation in dry ash-cement mixtures based on fly ash from TPS "Maritza-3" are experimentally studied and concrete samples are produced, whose tensile-strength parameters correspond to the Bulgarian standards.
The mineral and technological properties of wastes from the clinker repository of KZM "Plovdiv" and "The blue lagoon" of "Union miniere Pirdop" are studied and on their basis technological solutions are proposed for technologies for their ecological recycling and discharging.
A method is developed for producing chlorate defoliant - Mg-chlorate hexaureat, free of inorganic salts.
Synthesized and characterized are calcium-phosphate biphase bioceramics to be used as bone implants in the clinical practice.

The most important results obtained in the framework of international collaboration of CLMC are:

Construction of an effective filter system for purification of water using bentonite from the El-Fayum deposit, Egypt, in combination with clinoptilolite from Eastern Rhodopes, Bulgaria (with the National Research Center of Egypt).
Determination of crystal structures of new organic bases with potential applications in pharmacy (with the National Research Center of Egypt).
The mechanism of nucleation and crystallization of nanosized crystallites of zeolite A, which is an important microporous material for catalytic and ion exchange processes (University of Purdue, USA).

In the end of the year the activity of CLMC for a five year period was reviewed and it was concluded that all the projects worked out during this period resulted in important scientific and applied achievements.Among the most frequently quoted results in international journals are those concerned with studies on disordered systems, mineralogical problems, synthesis and characterization of microporous and nanosized materials and molecular sieves, theoretical methods for calculating vibrational spectra of inorganic materials, synthesis of nonlinear crystals for optics and laser applications. Generally, published were 1 monograph and 255 articles (154 in international, 8 in foreign, and 93 in national) in prestige specialized journals. Participation with 67 communications at 52 international scientific events was realized. On the other hand, 26 reports were presented at 16 national scientific conferences. Five patents were registered and supported financially during the period.

Our publication activity results also from 11 joint projects with scientists from institutes and universities in Germany, France, USA, Sweden, Israel, Japan, Italy, Spain, Portugal, Czech Republic, Egypt. In the framework of a grant-in-aid project with ICDD, USA, powder X-Ray diffraction data for new crystalline phases were precisely determined. The majority of these phases were synthesized in CLMC. Additional funding of 19 projects was supplied by the Research Fund of the Bulgarian Ministry of Education and Science, while of 5 projects by other Bulgarian institutions.

During 1999 CLMC was authorized to graduate specialists in the field of Mineralogy and Crystallography.

Nikola Zidarov
Sofia, January 2000

RESEARCH TOPICS:

I. MINERAL SYSTEMS:

1. Magmatic and metamorphic minerals and mineral associations in Serbo-Macedonian Massif (N. Zidarov, L. Macheva, P. Nenova, E. Tarassova, Y. Tzvetanova)

Investigations are carried out on the mechanisms of migmatization of metagranitoids cropping out in Maleshevska and Ograzden Mts. Field observations on the morphology of leuco-, meso-, and mellanosomes as well as the microstructural relations between minerals therein show that the porphyritic metagranitoids are more affected by the migmatization than the equigranular ones and the plagiogneisses. In regions where no clear differentiation between leuco- and mesosome is present, one can observe only slight segregation of salic minerals and rocks are distinguished by a relatively well preserved magmatic outlook. Regions of different size are observed, which, from a mineralogical point of view, are "ideal protoliths" for migmatization, but no indications for such a process are proved macroscopically. Evidently, the main reason for migmatization is the deformation being quite irregularly manifested in the rocks. At many places structures are observed, informative for the presence of a melt (e.g. xenomorphic quartz, intergranular albite surrounding the cludy pertite K-feldspar grains). Biotite-rich selveges which could be considered as melanosomes (in the meaning proposed by Ashwoth) are scarce and very thin (up to 1 mm). This makes a very questionable the widespread development of anatexis as a main mechanism of migmatization in the region under study. Evidently, under the varying P-T-X_fl conditions of metamorphism, usual for such areas, more than one mechanism of migmatization is possible. Moreover, one mechanism can provoke another, e.g. the external supply of water fluids favouring the subsolidus metamorphic differentiation, can lead to a partial melting.

Field and petrographic investigations of the rocks cropping out in the eastern part of the Belasitza Mt. were carried out. The results make it possible to distinguish metagranitoids and plagiogneisses of different degree of migmatization, plagioclase-bearing schists and schists containing garnet, kyanite, and staurolite. From the viewpoint of their structural position, mineral composition, microstructural features, deformation, and the degree of metamorphism, these rocks are analogues to those cropping out in the region of Maleshevska and Ograzden Mts.

For the first time melanocratic eclogites along dykes are found in the frame of the metamorphosed gabbroic body near G. Ribnitza village, Maleshevska Mt., similar to such formed near Gega village, Ograzden Mt.

Various pseudomorphoses, corona and diablastic structures of amphibole (aluminum-rich pargasite), garnet (Spess_1.414Py_25.495Gross_26.162And_4.252Alm_42.676), and plagioclase in the metagabbro are established.

Omphacite (Jd_8.558-22.886Ae_0-13.596) and garnet (Spess_1.691Py_17.481Gross_23.124And₀Alm_57.703) are formed in mellanocratic eclogites at temperatures 600-750^oC and pressures 13.5-17 kbar.

The post-eclogitic metamorphic processes are marked by a breakdown of omphacite to augite (Wo_49.85En_36.213Fs_13.935 ), plagioclase (An_15.7-23.4)and diopside (Wo_{30.386-50.847}En_{31.154-36.213}Fs_{13.465-18.655}). In addition, formed are tschermakite and pargasite as individual grains and coronas around the garnet (Spess_0.386Py_16.755Gross_28.273And₀Alm_54.604). According to geothermobarometry data the processes have started at temperatures 570-670^oC and pressures 12-13 kbar and further developed at temperatures 500-600^oC and pressures about 4 kbar.

2. Distribution of rare earth elements in natural fluorite (B. Zidarova)

The distribution of rare earth elements (REE) in fluorite from the main Bulgarian deposits (Slavyanka, Mikhalkovo and Chiprovci) is studied.

Fig. 1

Fig. 2

Fig. 3

Enrichment or depletion in REE of the investigated fluorite samples, normalized to their concentration in chondrites, the appearance of Eu and/or Ce anomalies, and the Sm/Ce ratio (see Fig.1) are typical of each fluorite variety separated in every deposit. The total REE content, as well as the content of lighter and heavier REE in fluorite depend on temperature, pH (see Fig. 2 and Fig. 3) and Eh of the mineral forming hydrothermal solutions.

3. Sedimentary-hydrothermal ore-forming processes in the Kremikovtsi deposit (Z. Damyanov)

Two distinct assemblages of authigenic phyllosilicates were distinguished in the Kremikovtsi SEDEX siderite iron formation (SIF), both being important tracers for the two styles of mineralization characteristic of this type of ore deposits [73]. The hydrothermal-sedimentary layer silicates are presented by sporadic finds of relict microcrystalline Mg-berthierine of a relatively low degree of structural ordering, as well as by its diagenetic transformation product, chamosite. The former mineral is closely associated with framboidal pyrite both cementing sparry siderite grains as an intergranular matrix. The hydrothermal-epigenetic phyllosilicates (berthierine, chamosite, illite-smectite, and kaolinite) from the barite-sulfide assemblage are characterized by: crystalline and undeformed habits, relatively large particle size, low-temperature polytypes, low-to-no mixed layering, high degree of crystallinity, the absence of impurities, dominant monomineral aggregates, affiliation to initial open spaces and deposition mainly as vug fillings and linings. The higher Al concentration in hydrothermal solution than that in the seawater determines the affiliation of phyllosilicates in the Phanerozoic SEDEX SIFs to aluminous species (berthierine, chamosite) unlike the low-to-no aluminous greenalite and stilpnomelane in the Precambrian IFs.

An important new evidence to distinguish the two aforesaid styles of mineralization is the vitrinite reflectance (R) of the associated organic matter (see the figure). The average value of R (of about 1.3%) of the organic matter accompanying the hydrothermal-sedimentary assemblages is consistent with the average value for the Middle Triassic carbonate sequence in the region, unlike the hydrothermal-epigenetic assemblages with average R of about 4.7%. These data show that: (1) dispersed organic matter in the Kremikovtsi SIF has undergone two-way thermal maturation caused by burial diagenesis and hydrothermal alteration; (2) the sedimentation of organic matter during siderite precipitation has been influenced by hydrothermal processes unlike that of the surrounding marine carbonate precipitates containing organic matter with approximately constant R of about 1.3%.

4. Mineralogical and geochemical investigation of Fe-Mn nodules from the Clarion-Clipperton zone, Pacific Ocean (V. Dekov, Z. Damyanov)

Detailed mineralogical and geochemical investigation of Fe-Mn nodules from the Clarion-Clipperton zone (2474 and 2483 polygons), Pacific Ocean, were performed. It is found that the morphology of the nodules (sedimentary type in 2474; sedimentary-diagenetic and diagenetic types in 2483) differs substantially due to: (1) the level of biological activity in the polygons; (2) the rate of sedimentation; and (3) the influence of bottom streams during the final stages of nodule growth.

Buserite of different crystallinity (high for the submerged in the bottom mud nodule parts; low for the upper ones), associated with birnessite and vernadite, dominates in the sedimentary nodules. The same mineral is also dominant in the sedimentary-diagenetic nodules. Its structural ordering increases with increasing of the Mn/Fe ratio and of the content of Cu and Ni. Localization of Mn, Cu and Ni in nodule cores, and of Fe and Co in nodule rims was established. A number of mineral, organic and aggregate inclusions (sulfides, oxides and oxyhydroxides, clay minerals, volcanoclastic materials, organic remains, etc.) of different origins were found in the nodules studied playing the role of either nuclei of nodule growth or by fixing the stages of slow growth. The content of Mn in the nodules is about 200 to 250 times that in the host sediments, while that of Fe - more than 2.5 times higher. This reflects the high Mn mobility and ability of concentration in the process of syn-diagenetic redistribution of the elements during the recent oceanic lithogenesis. The average values of the Mn/Fe ratio in the nodules from the 2474 polygon (about 1.8, typical of hydrogenetic nodules), and from the 2483 polygone (about 2.6, characteristic of sedimentary-diagenetic and diagenetic nodules) confirm the morphologic differentiation mentioned above. The lateral distribution of Mn, unlike that of Fe, is as follows: the content of Mn is high in the nodules from the bottom depressions, and low in the nodules from the abyssal ridges. The concentration of REE in the nodules is higher than that in the host sediments, and, as a whole, is similar to the average values for the Pacific Ocean nodules. The model of the distribution of REE reveals a positive Ce anomaly like that of the suspension deposited from the upper seawater.

5. Ni-Co-Fe-containing sulphoarsenides and sulphides and their mineral parageneses from the Zvezdel-Pcheloyad ore district, Eastern Rhodopes (E. Tarassova)

Amongst the widespread in Eastern Rhodopes polymetalic sulphide and sulphosalt mineralizations, Ni-Co-Fe sulphoarsenide and sulphide minerals were established in the Ralitza Dere locality, Sedeftche deposit, Zvezdel-Pcheloyad ore district. This ore mineralization is localized in the host marbles containing amphibolite layers. Two mineral parageneses, an earlier sulphide (predominant) and a later sulphosalt, were distinguished in this locality [36]. The sulphide paragenesis includes pyrite, marcasite, chalcopyrite (I) as major minerals and pyrrhotite and arsenopyrite as minor minerals. Pyrite, being the most widespread ore mineral of the paragenesis, demonstrates increased contents (wt.%) of Ni (to 4.56), As (to 2.74), Co (to 1.28), Cu (to 0.56) and Sb (to 1.51).

The minerals of the sulphosalt paragenesis, including nickeloan pyrite, bravoite, Ni-Co-Fe sulphoarsenides, tetrahedrite (most abundant), Ag-tetrahedrite, chalcopyrite (II), polybasite, galena, sphalerite, pyrrhotite (II), occur as veinlets and aggregates among the minerals of the sulphide paragenesis. Nickeloan pyrite (NiS₂ 20-29 mol. %) and bravoite (FeS₂ 32-66 mol.%, NiS₂ 16-57 mol.%, CoS₂ 11-18 mol.%) are the earliest minerals of the second paragenesis and are established as zonal rims arround veinlets crossing pyrite. The Ni-Co-Fe sulphoarsenides occur as (1) outer zone of pyrite-nickeloan pyrite-bravoite zonal aggregates, (2) pseudomorphs after pyrite crystals, and (3) individual grains or aggregates in quartz veinlets. The chemical composition of the sulphoarsenides demonstrates wide variations in the content (wt.%) of Ni (7.9-29.5), Co (3.1-21.4), Fe (1.44-7.69), As (31.8-55.8), S (12.5-25.4). Occasionally, the minerals contain Sb (to 11.3) and Cu (to 1.23). The cation-to-anion ratio is found to be close to the stoichiometric (1/2), while (As+Sb)/S atomic ratio demonstrates significant deviation from the ideal, being 0.60-1.91 (mostly - 0.88-0.98). According to the chemical composition, the sulphoarsenides can be classified as gersdorffite, Co-gersdorffite, Sb-gersdorffite and Ni-cobaltite.

The geochemical and mineralogical peculiarities of the Ralitza Dere ore mineralization are similar to those in other parts of the Sedeftche deposit. It seems that host rocks are the source of Ni and Co in the hydrothermal solutions.

6. Indicatory properties, stability and transformations of minerals in the Me₃O₄and (Me²⁺,Me³⁺)₂O₃systems: Fe-Ti oxides from the Granitovo pluton, Eastern Srednogorie (E. Tarassova)

Accessory magnetites and ilmenites from plutonic rocks in the multiphase Granitovo pluton and in the embedded therein gabbro xenolites are investigated as indicators for discrimination of the forming plutonic systems. According to the so far accepted opinions the Granitovo pluton is built up of three phases - quartzdioritic, granodioritic and granitic, while gabbro is in the form of xenolites of the rim facies of the Chernozem pluton. There are, however, other hypotheses which indicate that the gabbro is, in fact, the first phase of the Granitovo - Chernozem pluton. The content of accessory Fe-Ti oxides in the rocks is from <1 to 3 %. The size of magnetite crystals is from <0.01 to 0.8 mm, while that of ilmenite - from 0.01 to 0.4 mm, their content and sizes being maximum in the gabbro species. Both magnetite-ilmenite intergrowths and homogeneous magnetite are typical for the all rocks studied. Particular ilmenite crystals were found only in granodiorite and granite. In magnetites Mn, V, Si, Al, Mg, Ti, and Ca were established to present as impurities. Highest contents (wt. %) of Ti (up to 1.89), V (up to 1.86), and Al (up to 2.20) were measured in magnetites in gabbro varieties. Only in intermediate and acid rocks admixtures of Si (up to 1.80 wt. %), Mg (up to 0.44 wt. %), and Ca (up to 0.13 wt.%) were found. The content of Mn (up to 0.75 wt.%) are close to that for magnetites in all rocks. For ilmenites large variations in the content is observed for both the major chemical elements, Fe²⁺ and Ti, and the impurities Fe³⁺ and Mn. The study of the compositions obtained shows that the main part of gabbro contains ilmenite, while the intermediate and acid intrusive rocks include of Mn-ilmenite, Fe-pyrophanite and pyrophanite. The contents of hematite in ilmenite and pyrophanite for all intrusive rocks are close to each other and vary between 0 and 12.6 mol %. The distribution of the main impurities, Mn, V, Si, Al, and Mg, in the coexisting magnetites and ilmenites reveals polarity only in the spreading of V and Mn, V being concentrated in magnetite and Mn in ilmenite. The differences established in the amount, size and composition of the accessory magnetites and ilmenites (pyrophanites) in the basic, intermediate and acid rocks can support the idea that the rocks, which include magnetite and ilmenite, are products of the differentiation of various plutonic systems.

7. Platinum-group minerals from host rocks and placer deposits: phase composition, indicative features and associations, origin and transformation conditions (Z. Tsintsov)

Platinum-group minerals (PGM) are observed as very small sized (3-8 mm) inclussions in spinels from ultrabasites (Eastern Rhodopes, Kurdjali region). Asides, in the investigated materials are found native silver and acanthite [63](Koshtrava village) as well as native gold (Dobromirtsi village). The native silver is in the form of irregularly shaped grains of a size from 3-5 to 7-8 mm, rarely up to 20 mm. Acanthite is present as thin elongated platelets of width up to 3 mm and length up to 7-8 mm. Their general property is that no impurity elements are detected in their composition. It is assumed that the necessary Ag for the formation of the two minerals has been released from pyroxenes and amphiboles during serpentinization of ultrabasites. At 250^o C and normal pH, Ag is most probably mobilized as a Ag(HS)₂^- complex and the investigated minerals being formed under appropriate conditions.

Native gold was established in fiber-columnar type magnetite from ultrabasites [89]. The grains are irregularly shaped with an angular contour of approximately 80 mm in length and 18-20 mm width. Their composition is of only two elements, Au and Cu (from 3.68 to 9.42 at.%), while their purity is relatively high (from 854 to 969 %o). The found gold mineralizations are most probably of hydrothermal origin.

PGM of separate regions of sedimentary deposits of the Kustendil graben and of the Iskar river and its inflows to south of Sofia are investigated. These minerals are manifested (in a decreasing quantitative sequence) by individual grains of sperrylite, Pt-Fe alloys, Os-Ru-Ir alloys, laurite, and mertieite II. Bowieite and kashinite were observed only as inclusions in the Pt-Fe alloys.

The primary sources of a part of the discussed minerals (the alloys, bowieite, and kashinite) are most probably the unaltered ultrabasites from the bounding massifs of the graben. This suggests magmatic conditions of their formations. The rest minerals (sperrylite and mertieite II) most probably are of hydrothermal origin.

The preliminary data on PGM from sediments around the Iskar river have shown that the mineral association substantially differs quantitatively and, to some extent, in composition, as compared to the placer deposits of the same minerals in other parts of Bulgaria.

A new mineral species for Bulgaria is established, formed in the system Pt-Sn (±Cu), which is most probably niggliite (PtSn). The remaining PGM are presented, in a quantitatively decreasing sequence, by mertieite II, Pt-Fe alloys, sperrylite, ruthenium, and Os. All of them fall in the class <200 mm.

8. 1:25 000 mineralogical map of the heavy mineral concentrates in Bulgaria (O. Vitov)

Data on additional 30 892 mineralogical samples from heavy mineral concentrates (comprising 117 455 samples of the data base of Bulgaria) were mapped in a scale M 1:25 000 (see the figure). Mineral data for the Rila - Rhodopes and Kraishte areas are summarized to serve as a basis for mineralogical mapping of heavy mineral concentrates (M 1:100 000) [87] and prognosis for gold prospecting [85].

9. A model of thermal transfusion applied to the migration of gold in rocks (O. Vitov)

The study of distribution of gold in lithochemical dispersion aureoles have shown that gold is redistributed into thermal-gradient fields, thus forming a local minimum in zones of high temperature, symmetrical zones rich of gold and a peripheral zone supplied with gold from the embedding rocks. The thermal transfusion model proposed indicates that the main factor for modeling the gold distribution is the collision between gold atoms and the crystal matrix of the embedding rocks and their disruption. The source temperature and the rock thermal conductivity affect only the shape of the position of the anomaly.

In order to test the observed relationship and to scale numerically the model a brick from the wall of a furnace for black copper processing, Metalurgical plant "Pirdop", was studied, consisting of periclase and alumochromite. The brick has been used about 5 years in a thermal gradient of about 3000 deg.m^-1 and reveals a clear zonality in the chemical composition. The content of all chemical elements, including gold, which do not interact with the matrix and with the products of its thermal distruction, maximize in the same zone, in a good accordance with our theoretical model [88].

10. Geochemical peculiarities of soils in the region of Trans-European corridor No 8 along Dervena-Ranentsi, Kustendil district (O. Vitov)

The building of the European corridor 8 through the territory of Bulgaria in the region Kustedil-Gyueshevo necessitates to estimate the current state of the environment. For this purpose geochemical studies [47] were carried out of the layer lying beneath the humus and it is found that the region is contaminated with powder emissions (see the figure) from the tailing of MOK-Osogovo, Gyueshevo (area A), as well as from the usage of polluted with heavy metals water of Lebnitsa and Bistritsa (area B) rivers used for irrigation. At the same time, these studies confirm the tendency observed in the distribution of Pb [86], Zn, and Cu in the region (area C) and trace the prospecting of rare metals in the district of Dervena-Demirska mahala-Dolno selo.

11. Application of Na₂CO₃- ZnO decomposition to ICP-AES determination of boron in tourmalines (N. Lihareva, P. Kosturkova, Ts. Vakarelska)

The determination of boron in tourmalines is important for studies in genetic mineralogy and geochemistry as an indicator of tourmaline's origin. Recently, ICP-AES is one of the most widely used methods for detection of boron. Melting of Na₂CO₃-ZnO and water extraction of the melt is used to eliminate of the harming influence of the matrix elements [55]. The complete decomposition of tourmalines in the solution used and the degree of separation of the harming elements Si, Fe, and Ca are determined, which is a highly effective approach for such high temperature melting minerals. Experiments with synthetic mixtures and using the method of standard additions show that there is no adsorption and loss of boron during extraction of the melt. The method proposed for determination of boron in tourmalines provides results within the accuracy of other methods. A threshold of 4 mg/g can be achieved when 200 mg of the sample were analyzed within a precision of 5.2 % RSD. This method is suitable for determination of B in tourmaline samples with a high Fe/B ratio, where instrumental corrections are difficult and can be applied also for the determination of fluorine.

II. TECHNOGENIC MINERAL SYSTEMS:

12. Mineralogy and geochemistry of coals and coal products (S. Vassilev, C. Vassileva)

?he content, modes of occurrence and origin of Cl and Br in 34 coals from Bulgaria, Australia, USA, Japan, Canada, South Africa and Ukraine are characterized [66]. The relationships of Cl and Br concentrations with bulk chemical and mineral composition, rank, age, ash yield and geographic location of these coals are described. The favourable conditions for the enrichment of both elements in coal are also discussed. The concentration, modes of occurrence and behaviour of Cl and Br in combustion wastes from 11 Bulgarian coal-fired power stations (TPS) are characterized [67]. The main reasons for volatilization, condensation, capture and retention of both elements during coal combustion are also described. The results show that Cl and Br in bottom ashes, and particularly fly ashes, from TPS contaminate substantially air, soil, water and vegetation near TPS [67]. The phase-mineral composition of 6 types lignitic (Maritza East, Maritza West, Sofia), subbituminous (Bobov Dol, Pernik) and bituminous (Balkan) Bulgarian coals, treated by gradual oxidation and ashing from 100 to 1600°C via 100°C interval, are identified. The phase-mineral and chemical composition [43] and the content, modes of occurrence and sources of trace elements [45] in refuse-derived chars (RDC) from pyrolysis of municipal solid wastes are characterized. The behaviour, capture and inertization of some toxic and potentially toxic trace elements during combustion of this RDC are also discussed [44]. The preliminary characterization [46] and NO_X reduction tests [28] of low-cost catalytic sorbents, based on coal chars impregnated with petroleum ashes, are also reported.

13. Synthetic rocks (SYNROC) as an advanced approach to stable, longterm and environmental immobilization of radioactive wastes (I. Donchev, N. Zidarov)

Methods for disposal and conditioning of radioactive wastes (radwastes) are nowadays in a constant progress according to the International Atomic Energy Agency (IAEA) requirements. The conventional way for radwastes conditioning is to incorporate the radionuclides in borosilicate and aluminophosphate glasses. A new approach has been proposed recently suggesting the incorporation of high level waste in synthetic rocks (SYNROC). The main advantage of SYNROC is its specific mineral composition which is highly resistant under hydrothermal conditions in the radwaste repository.

SYNROC samples have been synthesized and studied as media for radwaste immobilization. The mineral composition of the products was determined by powder XRD, optical microscopy, and DTA/TG analyses. On the basis of our results a national program for investigation of SYNROC application to environmental protection is proposed [5].

III. MODELING AND MODIFICATION OF MINERAL SYSTEMS:

14. Geometrization of the fundamentals of Chemistry: Mathematical representation of chemical objects and processes (V. Penev, L. Konstantinov, M. Marinov)

In solving the problem of geometrization of the language of chemistry it is shown that:

The type and number of physical particles (neutrons, protons and valent electrons) absorbed or emitted by a simple chemical object is presented mathematically through corresponding kind of operators ()ⁿ,
()^m, and ()^h in the V_M(3);
The type and number of free physical particles [31] participating in chemical processes can be presented mathematically through defining the corresponding kind of free operators n, m, and h in the V_M(3).

On the basis of the aforesaid and previous results:

A method is developed for entire mathematical representation of arbitrary chemical processes.
In the framework of the proposed mathematical formalism in a general form formulated are lows for the electric charge preservation and the mass preservation in chemical reactions.
It is shown that in the V_S(6) space of chemical structures every simple chemical object can be presented geometrically by the corresponding chemical point, and every complex chemical object by the corresponding chemical graph.
It is shown that from the geometrical point of view the study of different chemical processes is in fact a study of transformation of the corresponding sets of chemical points and chemical graphs in the space V_S(6).

15. Structure model for a synthetic Pb-Sb Cl sulphosalt phase (V. Kostov-Kytin)

For rod-based sulphosalt structures based on the SnS or PbS archetype 12 layer types have been derived (E. Makovicky 1993, Eur. J. Mineral., 5, 545-591) specifying their geometric and compositional characteristics. These layer types differ in the way the rods in them are connected and the layers also may differ in the thickness and width of the lozenge-shaped rods. Furthermore, E. Makovicky created a two-dimensional classification of the known and hypothetical sulphosalt structures and explained the rather self-contained picture of known layer and match types as being a result of severe limitations put by a rule derived by him. It postulated as a primary condition for existence of a structure type in this family, the ability to match together layers of one type or a pair of layers of two distinct types with such N and N' values that they produce mutually compatible Q₁/H₂ and Q₂/H₁ interfaces, where N and N' are lozange width and thickness in terms of coordination pyramids and atomic layers, respectively, and Q and H denote the width of pseudotetragonal and pseudohexagonal surfaces of lozanges respectively.

Based on the geometric approach offered by E. Makovicky and on some common structural and chemical characteristics of already reported Pb-Sb Cl sulphosalts an attempt was made to predict the possible rod-layer combination in the structure of the synthetic Pb₁₁Sb₁₀S₂₄Cl₄ phase for which only lattice parameters and symmetry were known [54]. The alteration of Type 5 layers with those of Type 2 gave best results specifying P2/m as the only possible space group for this compound. Precise measurement of the interatomic distances (r) in the proposed structure has revealed that they do not go beyond the already established for other sulphosalt structures values, i. e., 2.4 ? < r < 3.9 ?. In addition, this structure model was supported by trivial calculations bringing to the new formula Pb₁₀Sb₉S_21.5Cl_3.5 in which the cationic and anionic ratios stay very close to those experimentally received.

16. Growth of the hexagonal prism on the crystals of a-quartz (M. Chr. Maleev, V. Kostov-Kytin)

Series of experiments were carried out in order to explain a possible mechanism for growing the hexagonal prism [56]. The crystallization proceeded at 370 ± 2.4°C at a temperature difference of 30 ± 4.8°C. Pebbles of natural quartz gravel (milky quartz) with diameters of about 8 mm were used as a nutrient. The solvent used was 0.5 M NaOH solution with some LiNO₂ added. Three different types of seeds were prepared for the runs: a) man-made quartz Z-cut plates (parallel to c {0001}); b) pure natural quartz crystals, elongated along the c axis and c) three pieces cut from a single natural quartz crystal elongated along the c axis. The run-products of this last case were most indicative of the mechanisms for the quartz crystals growth. In those sectors where growth of the hexagonal prism takes place typical Brewster's figures were observed on polished pinacoidal cuts in transmitted light and crossed nicols. This is a sign for twinning after the Brazil twin law. The amount of Brazil twins is considerably bigger at the entrance angles where the growth rate of m{}reaches about 0.1 mm per day. Sections cut from all crystals were subjected to weak superficial dissolution in NH₄HF₂ to reveal better their zonal and sectoral structure as well as the morphology of the grown faces. Based on this investigations, the following conclusions were drown:

In the presence of Brazil twins or a big amount of dislocations the growth rate of the hexagonal prism m{}increases and comes closer to the one of the main rhombohedra. Growth pyramids with specific morphology are formed in the process of m{}growing.
At the absence of Brazil twins or dislocations the quartz crystal growth is dominated by the main rhombohedra z{} and r{}. In this case, horizontal striation appears, typical for quartz.
The integration of three or more crystal species is possible with a subsequent formation of a single but already twinned quartz crystal.

17. Chemical and structural transformations of tungsten minerals under low-temperature (exogenic) conditions: experiment, analysis and modelling (M. Tarassov, N. Khaltakova)

Fibrous nanocrystals with composition WO₃.(0.10-0.12)Fe₂O₃ .nH₂O and average size ~20 nm in length (variations 5-100 nm) and ~1.5 nm in width (variations 1-4 nm) were established in the products of the supergenic alteration of scheelite. The nanocrystals are grouped in the form of plate elongated textures sized about 250?20 nm² which build up three-dimensional networks macroscopically visible as white disperse aggregates.

It is shown that the nanocrystal structure can be derived from the structure of WO₃.1/3H₂O (Fmm2), thus demonstrating the prsence of disorder in the alternation of the hexagonal tungsten bronze type layers in [001] direction (Fig.a). Iron atoms randomly occupy free octahedral cavities situated between every two adjacent (001) layers of the WO₃.1/3H₂O structure. Figure b demonstrates a two-layered fragment of the fibrous nanocrystal, seen along [001], where the shaded octahedra exhibit the iron atom positions (occupation is about 1/3).

Insertion of iron atoms into the structure of the nanocrystals makes them more stable during thermal treatment as compared to the pure WO₃.1/3H₂O phase. Thermochemical investigations indicate that the nanocrystals remain stable to 600^oC, while the WO₃.1/3H₂O phase is known to decompose at 250^oC. Raman spectra of the nanocrystals are found very close to those of WO₃.1/3H₂O. In addition, a weak peak at 880 cm^-1 appears and a decrease in intensity of the peak at 960 cm^-1 is observed, typical of tungsten oxide hydrates and attributed to the stretching vibration of the W=O bond.

The formation of WO₃.(0.10-0.12)Fe₂O₃ nanocrystals with disordered structure of WO₃.1/3H₂O is in a good agreement with earlier experiments and model studies of the CaWO₄?WO₃.1/3H₂ O conversion, which is assigned to a topotaxic process facilitated by similar atomic configurations (base building blocks) in both phases [34].

18. Structural model of Al₁₃-pillared montmorillonite (V. Dimov, A. Ilieva, N. Khaltakova, L. Filizova)

Alumina-pillared montmorillonite is prepared by intercalation of polyoxyhydroxy aluminum cations - [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺ of a natural montmorillonite from Dimitrovgrad deposit, Bulgaria. Transmission electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and BET methods are used to study the untreated and pillared forms of the montmorillonite. A structural model involving deformed Al₁₃pillars is proposed [52]. The model is based on literature data and on a comparative investigation using transmission electron microscopy (TEM) on a natural Ca-rich montmorillonite of low-iron content and relatively high layer charge as well as on its Al₁₃ -pillared analogue.

Four deformed pillar types (Fig.1) are derived based on the orthogonal model of the pillar to conform to C2/m symmetry.

These pillars are distributed uniformly over the interlayer cation positions of montmorillonite. This is possible if one occupied (O) position alternates with the same number of vacant (V) positions along the [100], [], and [] directions within a single interlayer (different O-V alternations).

Fig. 1

Fig. 2

Structural models of montmorillonite pillared by polymeric Al₁₃-cations were prepared using the following steps: (a) development of a hypothetical structural model of natural montmorillonite, ordered along the c axis; (b) modification of this ordered hypothetical structure by enlargement of the interlayer distance - "enlarged-interlayer montmorillonite"; (c) modeling of the Al₁₃ pillar; and (d) arrangement of the pillars between the layers of the enlarged-interlayer montmorillonite structure.

The chemical data indicate that one Al oxy-hydroxy ion is intercalated on the average every 4.2 montmorillonite unit cells. Therefore, one of 8.4 interlayer pillar sites is occupied, while 7.4 are vacant, i.e., the observed pillar site occupancy is 11.9 %. The calculated pillar-site occupancy of 11.1% of the OVVO alternation (Fig.2) is closest to the observed pillar occupancy equal to 11.9 %, as determined from the chemical data.

The validity of the model is tested by comparing the observed TEM electron diffraction patterns (EDP) with simulated EDP using the multi-slice method. Simulated EDP of the models of the pillared montmorillonite were compared to patterns from the enlarged-interlayer montmorillonite with Al site occupancies corresponding to the OVVO alternation and were compared to the experimental EDP of the pillared montmorillonite. The patterns are of the same geometry for each given direction.

The model explains the structure of a pillared montmorillonite with differing distributions of the pillars in the interlayer and the increased degree of ordering along the c axis of the pillared form compared with the untreated montmorillonite.

19. Characterization of calcium phosphate phases obtained during the preparation of sintered biphase Ca-P ceramics (O. Petrov, E. Dyulgerova, L. Petrov, R. Popova)

Chemical, powder X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) methods were used to control the reproducible preparation of calcium-phosphate (Ca-P) biphase ceramics for clinic bone implantation. The synthesis of hydroxyapatite + alpha-tertiary calcium phosphate (HAP + a-TCP) and hydroxyapatite + beta-tertiary calcium phosphate (HAP + b-TCP) bioceramics is achieved under controlled conditions: the calcium-to-phosphorus (Ca/P) ratio, the phases contents and the texture of the sintered material [57].

20. Thermal decomposition products of hydrotalcite-like compounds: low-temperature phases (Tz. Stanimirova, I. Vergilov, G. Kirov, N. Petrova)

Synthetic hydrotalcite-like samples with composition [M_1-X²⁺ Al_X³⁺(OH)₂] (CO₃)_X/2 . nH₂O, where M=Mg, Ni; x=0.25 and 0.33; n=2x and 1.5x, are studied by XRD, DTA, TG, and IR spectroscopy after heating in the temperature range 120-260°C and subsequent rehydration in air and water. As a result, two metaphases are obtained. Metahydrotalcite, D(HT-D), is formed at 140-180°C by reversible dehydration of the interlayer. Metahydrotalcite, B(HT-B), is formed at temperatures from 240 to 260°C as a result of the dehydroxilation of a part of the OH groups in the brucite-like layer and inclusion of two oxigen atoms from the CO₃-group in the same layer. The HT-B phase has a specific crystal structure. Rehydration does not restore the initial structure, but leads to the formation of a phase (HT-B-r) characterized by a higher thickness of the interlayer, a high content of water and low temperature of dehydration. The properties of HT-B depend on the ratio M²⁺/ Al for the initial sample. The substitution of Mg for Ni in the low temperature region does not influence the properties of the metaphases [33].

IV. MICROPOROUS MINERALS AND ANALOGUES

21. Structural, physical and chemical properties of microporous titanosilicates (V. Valtchev, S. Mintova)

The structure and properties of ion-exchanged forms of the newly synthesized K₂TiSi₃O₉.H₂ O phase were studied [42]. It is shown that this material can be totally exchanged by NH⁴⁺ ions and partially by various alkaline cations, but the two independent crystallographic cation positions therein are non-equivalently occupied. Depending on the type and amount of the exchanged cations one can control some physical and chemical properties such as the thermal stability and the water adsorption capacity.

22. Nanosized colloidal zeolites and thin films of microporous materials (S. Mintova,`V. Valtchev, B. Mihailova)

The crystallization of discrete particles of zeolite A, zeolite Beta and zeolites of the type FAU is investigated [23, 38, 62, 65]. Using DLS, XRD, HRTEM, and TG methods the initial stages of nucleation and crystallization of microporous phases are specified [12, 24, 25, 41]. Films thick up to 100-1000 nm are synthesized using colloidal zeolite particles and the crystallographic orientation of the crystallites forming the film is studied by XRD [8, 9, 20, 21, 22, 37, 53].

V. SYNTHESIS, COMPOSITION STRUCTURE AND PROPERTIES OF NEW CRYSTALLINE MATERIALS:

23. Structure of molecular adducts of inorganic salts. VIII. Thiourea Complexes of Cadmium Nitrate (R. Petrova, S. Bakardjieva, T. Todorov)

Additional compounds were established in the system Cd(NO₃)₂ -tu-H₂O, tu = thiourea, three Cd(NO₃)₂.ntu (n = 2, 4). The monoclinic Cd(NO₃)₂.2tu, space group P2₁/n, a = 4.267(1), b = 11.956(1), c = 11.330(1)?, b = 100.22(6)° has crystal structure built up of neutral [Mtu₂.(NO₃)₂] centrosymmetric complexes. There are two polymorphic modifications (I and II) when n = 4, which coexist under ambient conditions. These Cd(NO₃)₂.4tu polymorphs were found to be monoclinic, space group P2₁/c. Their cell parameters are a = 21.380(3), b = 5.975(1), c = 17.531(4)?, b = 122.56(2)° for (I) and a = 12.811(3), b = 9.157(1), c = 15.770(2)?, b = 91.20(1)° for (II). Their structures consist of complex [Mtu₄]²⁺ cations and NO^3- anions. There are extensive networks of weak hydrogen bonds which held the structural units together.

24. Crystal structures of Cd(ReO₄)₂.4Urea, Cd(ReO₄)₂.6Urea and Ca(ReO₄)₂.5Urea. Synthesis and characterization of urea adducts from the systems M(ReO₄)₂-Urea-H₂O, M = Ca, Sr, Ba, Pb and Cd (R. Petrova, T. Todorov, S. Bakardjieva, B. Mihailova, O. Angelova)

The crystal structutes of Cd(ReO₄)₂.4Urea, Cd(ReO₄)₂.6Urea and Ca(ReO₄)₂.5Urea were solved [32]. Cd(ReO₄)₂.4Urea consists of discrete neutral [Cd(ReO₄)₂L₄] (L = Urea) clusters. Ca(ReO₄)₂.5Urea and Cd(ReO₄)₂.6Urea are built up of cationic [Ca(ReO₄)L₅]⁺ and [CdL₆]²⁺ clusters, respectively, and ReO₄^- anions, interlinked by an extensive network of H-bonds. The octahedral coordination of M atoms is most regular in Cd(ReO₄)₂.6Urea and most distorted in Ca(ReO₄)₂.5Urea. With the synthesis and X-ray analysis of these new urea adducts the investigation of the systems M(ReO₄)₂-Urea-H₂O, M = Ca, Sr, Ba, Pb and Cd, was accomplished.

25. Synthesis and structure of Pd(II) complexes of 1,2,3-triphenylguanidine (N. Mincheva, T. Todorov, O. Angelova,P.J. Bailey, M. Miteva)

The formation of two complexes by reaction of [PdCl₄]^2- with 1,2,3-triphenylguanidine (PhNH)₂C=NPh under different metal/ligand ratios was studied and the structure of the complex [(1,2,3-triphenylguanidine)₂PdCl₂ ] was determined by X-ray diffraction methods. The ligands are coordinated as neutral monodentate molecules to the metal centre through their imine nitrogen atoms. The second Pd(II) complex is [Pd(1,2,3-triphenylguanidine)₄]²⁺ and was isolated by precipitation with ClO₄^-.

26. Synthesis of Magnesium Chlorate Defoliants (K. Kossev, T. Todorov)

The application of chlorate defoliants, especially in cotton production, results in an increase in the content of salts in the soil due to their great amount during preparation without affecting the synergetic effect. The purification of these salts is a difficult process under the existing manufacturing conditions. A new method for preparation of magnesium chlorate hexaureate, free of inorganic salts, is developed. Our investigations concern the phase composition and the interactions in the system magnesium salts - sodium chlorate.

Magnesium chlorate hexaureate was synthesised by the reaction of magnesium sulphate hydrate with sodium chlorate and urea. The process was optimised and a complete purification of the inorganic salts as by-products was achieved.

The developed method of synthesis is alternative to the methods applied in industry to producing "magnesium chlorate - defoliant". Its implementation and the procedure for preparation by the proposed method would lead to a decrease in the soil salt content. Magnesium chlorate hexaureate acts as a "soft" defoliant and has potential applications in the cultivation of cotton and other plants.

Laboratory samples were prepared and presented on the Exhibition dedicated to the 130 anniversary of the Bulgarian Academy of Sciences.

27. Solvents in the system BaO-B₂O₃ suitable for the growth of NdAl₃(BO₃)₄ crystals (D. Shumov, A. Nenov)

The choice of solvents in the BaO-B₂O₃ system for growing NdAl₃(BO₃)₄ (NAB) crystals is studied in detail. Four different compositions, BaO?1.6B₂O₃,BaO?2B₂O₃, BaO?3B₂O₃and BaO?4B₂O₃, are cosidered as possible systems for the crystal growth. The temperature and concentration regions for crystallization of the NdAl₃(BO₃)₄phase were determined for the NdBO₃-AlBO₃-BaO?1.6B₂O₃, NdBO₃-AlBO₃-BaO?3B₂O₃and NdBO₃-AlBO₃-BaO?4B₂ O₃ systems. The phase diagram of the only system, investigated so far, namely NdBO₃-AlBO₃-BaO?2B₂O₃(see the figure), is corrected and discussed [58].

Comparison between experimental conditions used for the NdAl₃(BO₃)₄phase to be synthesed from the four solvents is carried out in order to specify the most suitable solvents.

28. High-temperature Raman study of the phase transition in the clinopyroxene kanoite, MnMgSi₂O₆ (N. Zotov, T. Arlt)

Pyroxenes are important rock forming minerals and major components in the Earth's upper mantle. Clinopyroxenes with low Ca, Na content undergo displacive phase transitions at both high temperatures and high pressures which have attracted considerable attention. However, the nature of the phase transitions is not fully understood. Recently, the phase transition in kanoite (MnMgSi₂O₆ clinopyroxene) has been studied by high-temperature single crystal X-ray diffraction. It undergoes a displacive phase transition from space group P2₁/c to C2/c, isotypical to those described in pigeonite, clinoenstatite, and clinoferrosilite. Kanoite is of special interest because the transition temperature is much lower than in other clinopyroxenes, between 150 and 400^o C, depending on composition. This allows studies to be performed on the nature of the displacive phase transition without taking into account cation order-disorder phenomena.

The irreducible representations of the long-wavelength optical phonons were determined using the correlation method. In the low-temperature phase G_opt = 30 A_g + 30B_g +29A_u +28B_u. In the high-temperature phase G_opt = 14A_g + 16B_g +13A_u +14B_u. In both phases the gerade (g) modes are Raman active while the undergrade (u) modes are IR active. The assignment of the vibrational modes was performed by lattice dynamics and Raman intensity calculations.

Different behaviour of the Raman active modes as a function of temperature is observed. Several modes shift significantly below the phase transition temperature T_c about 290^oC to lower frequencies with increasing temperature, while other modes exhibit only minor frequency changes. Evidently, the former are strongly coupled, while the later are only weakly coupled to the order parameter. The splitting (Dn) of the A_g peaks at 660 cm^-1 below T_c provides a convenient measure of the temperature dependence of the order parameter. The fitting of Dn to the expression Dn = A(T_c-T)^b gives T_c = 290.4 ± 7.6^oC and critical exponent b=0.27±0.04. These results show that for kanoite the coupling of the A_g modes to the order parameter cannot properly be described by taking into account the lowest coupling terms only.

29. Vibrational and electronic states in defect complex materials (L. Konstantinov, B. Mihailova, E. Dinolova, M. Gospodinov, G. Bogachev)

The following two trends of investigation were carried out:

1) Point defects in complex optical-active single crystals [16, 17, 18, 19]: Using Raman spectroscopy single crystals of Bi₂(MoO₄)₃, Bi₄Ge₃O₁₂ doped with Mn in variuos concentrations, and two types of sillenite-structured single crystals, Bi₁₂(Bi_0.53Mn_0.47)O₂₀ and Bi₁₂TiO₂₀: X (X=Al, P, V, Cr, Mn, Cu, Cd, Co, W, Mo, Nd, and Ag).

The measured spectra were interpreted on the basis of calculated vibrational modes of structural units typical of these materials. Analyzed were the changes in the local structure, topology and interatomic forces of interaction of the embedding crystalline matrix due to incorporation of additional atoms. On the basis of these results one can correlate the microscopic changes in the structure and the macroscopic properties of the materials studied.

2) Vibrational and electronic states in microporous materials [10, 74]: Through reflectance-absorption infrared spectroscopy studied are the vibrational states of a monolayer of organo-silane molecules in nanosized films of microporous material Silicallite-1. By modeling the experimental spectra the structure of the short- and intermediate-range ordering and the degree of disorder is studied. The results obtained make it possible to follow the process of synthesis of thin zeolite film formation. The electron states in zeolite-type K₂TiSi₃O₉.H₂ O are studied by the DV-Xa claster method. A good agreement between experiment and theory is obtained in the spectral range 180-500 nm. It is shown that the intense absorption band in this region results from electron transitions between oxygen and titanium states and the experimentally observed splitting of the absorption band is due to contribution of potassium cations to the atomic interactions in the system of SiO₄ tetrahedra and TiO₆ octahedra.

30. Crystal structure identification of Bi₂(MoO₄)₃ single crystals (D. Nihtianova, V. Ganev, N. Khaltakova, M. Gospodinov)

Single crystals of Bi₂(MoO₄)₃ are interesting as materials for construction of acoustooptic devices due to their strong optical anisotropy, high acoustooptic figure of merit and low acoustic attenuation. Till now such crystals have been grown by the flux method and the crystal structure of Bi₂(MoO₄)₃ has been determined by X-ray single crystal diffractometry in space group is P2₁/c with lattice constants a=7.685(6), b=11.491(16), c=11.929(10)?, b=115.40(2)^o.

We investigated these crystals by Philips EM 420-T/EDAX. Four ([100], [010], [001], [120]) selected area electron diffraction (SAED) patterns from several particles are obtained and analyzed. The known structure model is tested by comparing the theoretical multislice calculated EDP and the four experimental SAED patterns of Bi₂(MoO₄)₃ single crystals. The calculations are performed separately for each of the four experimental microdiffraction patterns. The thickness of the specimen is determined independently for each of the patterns. All calculations are carried out in zero order Laue zone approximation (ZOLZ).

The pattern along [010] zone axis is photographed in two camera lengths: L135 and L480. The ZOLZ and FOLZ are observed with the shorter camera length. Observation of the first-order Laue zone is important to specify the crystal properties. Our [010] ZAP taken with the shorter camera length is identical to the theoretically drawn pattern for the monoclinic system ( [010] zone axis, case c//(010), mP, P1c₁) (see the figure).

This TEM investigation shows that the structure model known so far for Bi₂(MoO₄)₃ is in a good accordance with all the four diffraction patterns obtained by us. The estimated thickness of the particles in the range 80-180? is in a good agreement with their platy appearance.

VI. STRUCTURE AND PROPERTIES OF DISORDERED SYSTEMS:

31. Raman spectroscopy of water containing rhyolite and basalt glasses (N. Zotov, J. R. Sowbery)

Water has a substantial effect on the properties of silicate melts. However, the exact interaction between water and the structural units especially in aluminosilicate melts and glasses are still a matter of some debate. In order to try to address this, Raman spectra were obtained from a series of rhyolite and basalt glasses with varying water contents.

The nonpolarized spectra of the hydrous rhyolite glasses are typical for high silica glasses with low degree of depolymerization. Systematic changes are observed with increasing total water content (TWC). The strong low-frequency band at about 480 cm^-1, which arises mainly from bending and rocking modes of the T-O-T linkages narrows indicating that the T-O-T bond angle distribution becomes narrower with increasing TWC. The peak at about 580 cm^-1, which is usually assigned to 3-membered rings, disappears in the samples with TWC above 4 wt.% H₂O. The intensity of the 800 cm^-1 band, which arises from complex motions of the silicon atoms in Q⁴ units, decreases systematically with increasing TWC, which clearly indicates that the structure becomes more depolymerised. This is further confirmed by the increase of the intensity of the 910 cm^-1 band which is commonly assigned to T-OH bending vibrations. Subtle changes in the high-frequency band indicate changes in the Q-species distribution without significant increase of the Q³species. The O-H streching band extends from 2900 to 3700 cm^-1 and shows a linear increase in intensity with increasing TWC. The O-H bands indicate that there is a broad distribution of hydrogen-bond lengths in all samples regardless of the OH-H₂O distribution, which means that in all samples both the OH groups and H₂O molecules participate in hydrogen bonding.

The nonpolarised Raman spectra of the basalt glasses clearly indicate that their structure is much more depolymerised. The T-O-T band is shifted to higher frequencies and indicates that the T-O-T bond angle distribution in the basalt glasses is broader. The intensity of the 800 cm^-1 band is much weaker than in the rhyolite glasses and with increasing water content decreases further. This again is a clear indication of much larger depolymerisation. The high frequency band at about 1000 cm^-1suggests the presence of mostly Q²and Q³ species. With incresing total water content above 3 wt.% the relative intensity of the 1000 cm^-1 band decreases at the expense of increased intensity around 850 cm^-1. This suggests that the relative amount of Q³ species decreases probably at the expense of Q¹ species. The high-frequency band in the basalt glasses is broader than in the rhyolite glasses which implies larger bond-length and bond-strength short-range disorder in the basalt glasses. A weak peak at about 650 cm^-1 is observed in the basalt glasses. Polarized measurements show that this peak possesses a low depolymerization ratio and thus arises from symetric-type vibrations. Although the behaviour of this peak implies changes in the structure, additional studies are necessary in order to elucidate the origin of this peak in basalt glasses. Finally, the shape of the O-H stretching bands in the hydrous basalt glasses are very similar to those in rhyolites, but extend from 2700 cm^-1 to 3700 cm^-1. This leads us to the conclusion that the environment of the O-H bonds in the investigated polymerised and depolymerised aluminosilicate glasses are generally the same, and that the increase in the degree of depolymerisation leads only to an increase in strongly hydrogen bonded OH groups.

32. Silica species in aqueous fluids at high temperatures and pressures (N. Zotov, H. Keppler)

Preliminary in-situ experiments using an externally heated diamond anvil cell showed that H₄SiO₄ is the dominant silica species in aqueous fluids in equilibrium with solid quartz. These experiments are extended in this work to larger frequency, temperature and pressure. Up to 600^o C essentially only one band is seen at 760-785 cm^-1 which has been previously assigned to the symmetric stretching vibration of H₄SiO₄ molecules in agreement with the accepted models of silica speciation in water. At temperatures above 600^o C additional bands develop in the Raman spectra. These broad bands at 630, 920, and 930 cm^-1 are possibly due to an additional silicate species coexisting with H₄SiO₄. The most simple silica species aside from orthosilicic acid would be pyrosilicic acid H₆Si₂O₇, which could form according to the polymerization reaction 2H₄SiO₄=H₆Si₂ O₇ + H₂O.

Calculations of the normal frequencies, isotopic shifts and Raman intensities of H₄SiO₄, H₆Si₂O₇, and partially deprotonated H_4-nSiO₄^n- molecules confirm such assignements and indicate that at typical crustal pressures and temperatures the presence of high concentrations of ionized species in the solution can be neglected.

At low temperatures and pressures where only H₄SiO₄ species are observed the integral intensity of the characteristic peak of the orthosilicic acid should be proportional to the molar concentration of dissolved quartz. The logarithmic plot of molar concentration vs. the peak intensity shows that H₄SiO₄ is the only species present at 500-600^o C and 6-10 kbar pressures.

Using the integral intensities of the characteristic Raman bands, we estimated the equilibrium constant of the polymerization reaction 2H₄SiO₄ = H₆Si₂O₇ + H₂O. The required scattering cross-sections were taken from Raman intensity calculations. The enthalpy of the polymerization reaction is about 30 kJ/mol. It appears that with increasing temperature polymerization intensities.

33. Ion-mass transport in anhydrous basaltic melts in electric field (N. Zidarov, J. Muchovski, M. Marinov, M. Tarassov, N. Zotov)

Transport processes in anhydrous basaltic melts were investigated experimentally in a rectangular shaped electrochemical cell under an imposed constant electric field of intensity from 0.11 to 1.26 V/cm and temperatures between 1500 - 1600 K [69, 90]. With increasing the temperature in this range the melt viscosity was found to decrease from 3200 to 1170 Poise, its electrical conductivity changing from 3x10^-5 to 20x10^-5 W^-1.cm^-1, while the ratio of the activation energies of the two processes varies from 1.02 to 1.56. Frozen diffusion profiles for basaltic samples annealed abruptly and quenched under an external electric field voltage of 400 mV were studied.

The mass transport processes in the samples were investigated by microprobe analysis and were described through a set of differential equations for the non-stationary multicomponent chemical diffusion within the approximation of effective diffusion coefficients of the components. The equations were solved with imposing semi-infinite boundary conditions and expressions were found for the concentration dependency of the components and for the corresponding partial densities of the ionic current as functions of the distance between the cell electrodes. These expressions were used to fit the experimental profiles for the iron- and magnesium-oxide components in order to find values for their effective diffusion coefficients. The obtained values are of the order of 10^-7 cm².s^-1, while the corresponding values of the ionic mobility is of the order of 10^-6 cm².s^-1.V^-1. It is calculated that within the boundary diffusion current approximation Fe and Mg components in the melt would be transported at a distance at about 5 m towards the wall of a magmatic chamber for 100 years (see the figure). Consequently, during periods of time short from a geological point of view, electrochemically generated macroinhomogeneities can occur, influencing to some extent the crystallization processes.

The mass transport processes in basaltic melts were further studied in a square-sectioned electrochemical cell by varying the following parameters: the electrical field intensity from 0.18 to 2.18 V.cm^-1, annealing duration from 9 to 25 h, and temperature between 1270 and 1330^o C. On the basis of these data temperature dependencies were obtained for the melt electric conductivity and viscosity and the values of the activation energies were specified.

INTERINSTITUTES PROGRAMS:

Mineralogical, physic-chemical and crystal-chemical investigations of natural zeolites and sorbents. A collaboration with the National Research Centre, Egypt.
Single crystalline structural analyses and phase identification of new crystalline materials. A collaboration with the National Research Centre, Egypt.
Nanosized colloidal zeolites: synthesis, characterization and application. Interinstitute project with the Ludwig Maximilian University of Munich, Germany.
Synthesis of microporous zirconium silicates built of mixed coordination units. A collaboration with CNRS, University of Upper Elsace, France.

POSTDOCTORAL FELLOWS, POSTGRADUATED STUDENTS AND VISITING SCIENTISTS:

Dr. Boriana Mihailova – Lulea University, Sweden
Dr. Georgi Georgiev – NASA Laboratories, Virginia, USA.
Dr. Nadya Petrova – Ube University, Japan.
Dr. Nicolay Zotov – Bayrisches Forschungsinstitut fur experimentelle Geochemie und Geophysik, Universitaet Bayreuth, Deutschland
Dr. Valentin Valtchev – Ecole nationale superieure de Chimie de Mulhouse, France
Dr. Svetlana Mintova – University of Pordue, USA; Ludwig Maximilian Universitat, Munchen, Deutschland.

PUBLICATIONS AND REPORTS AT CONFERENCES AND LOCAL MEETINGS:

PUBLISHED ARTICLES AND REPORTS:

1. Buchvarov, I., P. Tzankov, V. Stoev, K. Demerdjev, D. Shumov. 1999. Generation of high-power picosecond pulses by passively mode-locked Nd:YAG laser using frequency doubling minor. - In: Advanced photonic with second order optically nonlinear processes, A. Boerdman et al., eds., Kluwer Academic Publishers, 197-200.

2. Georgiev, G., E. Georgieva, L. Konstantinov. 1999. Angular and power characteristics of noncollinear acousto-optic tunable filters. - Optics and lasers in engineering, 31, 1-12.

3. Georgiev, G., L. Konstantinov. 1999. Study of characteristics of noncollin?ar acousto-optic tunable filters. - Optik, 110, No 12, 545-553.

4. Dekov, V., Z. Damyanov, G. Kamenov, I. Bonev, K. Bogdanov. 1999. Native copper and a-copper-zinc in sediments from the TAG hydrothermal field (Mid-Atlantic Ridge, 26^oN): nature and origin. - Marine Geology, 161, 2-4, 229-245.

5. Dontchev, I., N. Zidarov. 1999. Synthetic Rocks (SYNROC) as an advanced approach to stable, long-term and environmentally suitable immobilization of radioactive wastes. - Geology and Mineral Resources, 6, 28-32 (in Bulgarian with English abstract).

6. Dontchev, I., B. Zidarova. 1999. Mineralogocal-technological studies of products from the copper slags dressing plant "Union Mineral Pirdop Copper". - Geology and Mineral Resources, 2, 13-16 (in Bulgarian with English abstract).

7. Dontchev, I. 1999. High-temperature aluminium phases in metallothermic ferroalloy slags. - Comp. rend. Acad. bulg. Sci., 52, 5-6, 69-72.

8. Hedlund, J., S. Mintova, J. Sterte. 1999. Controling the preferred orientation in silicalite-1 films synthesized by seeding. - Microporous and Mesoporous Materials, 28, 185-194.

9. Hedlund, J., S. Mintova, J. Sterte. 1999. Preferred orientation in thin silicalite-1 films synthesized by seeding. - In: 12^th Intern. Zeolite Conf., Materials Res. Soc., 1809-1816.

10. Ivanov, O., L. Konstantinov. 1999. Temperature dependence of the surface photo-charge effect in CdS. - Appl. Surf. Sci., 143, 101-103.

11. Kamenov, G., V. Kostov-Kytin, O. Petrov. 1999. Sr-Bearing Chabazite from the Kayryaka Quarry, Bourgass Region, Bulgaria. _ Compt.rend.Acad.bulg.Sci., 52, 9-10, 59-62.

12. Landau, M., D. Tavor, O. Regev, M. Kaliya, M. Herskowitz, V. Valtchev, S. Mintova. 1999. Colloidal nanocrystals of zeolite Beta stabilized in alumina matrix. - Chem. Mater., 11, 2030.

13. Lenchev, A., Dontchev, I., L. Gigova. 1999. Investigations of fly-ashes from EPS for production of mixed cements. - CEMENT and its application, (march-april), 36-38 (in Russian).

14. Lihareva, N., K. Mitov. 1999. Determination of arsenites and arsenates in sediments. - Mining and Geology, 54, 6-7, 47-49 (in Bulgarian with English abstract).

15. Masheva, V., M. Grigorova, D. Nihtianova, J. Schmidt, M. Mikhov. 1999. Magnetization processes of small g-Fe₂O₃ particles in non-magnetic matrix.- J.Phys.D: Appl. Phys., 32, 1595-1599.

16. Mihailova, B., D. Toncheva, M. Gospodinov, L. Konstantinov. 1999. Raman spectroscopic study of Mn-doped Bi₄Ge₃O₁₂. - Solid State Communications, 112, 11-15.

17. Mihailova, B., G. Bogachev, M. Gospodinov, L. Konstantinov. 1999. Raman spectroscopic study of Bi₂(MoO₄)₃. - J. of Raman Spectroscopy, 30, 195-198.

18. Mihailova, B., G. Bogachev, V. Marinova, L. Konstantinov. 1999. Raman spectroscopy study of silenites. II. Effect of doping on Raman spectra of Bi₁₂TiO₂₀. - J. of Phys. and Chem. of Solids, 60, 1829-1834.

19. Mihailova, B., M. Gospodinov, L. Konstantinov. 1999. Raman spectroscopy study of sillenites. I. Comparison between Bi₁₂(Si,Mn)O₂₀ single crystals. - J. of Phys. and Chem. of Solids, 60, 1821-1827.

20. Mihailova, B., V. Engstrom, J. Hedlund, A. Holmgren, J. Sterte. 1999. Infrared spectroscopic study of a g-mercaptopropyl-trimethoxysilane monolayer on a gold surface. - J. of Materials Chemistry, 9, 1507-1510.

21. Mihailova, B., V. Engstrom, J. Hedlund, A. Holmgren, J. Sterte. 1999. A vibrational spectroscopic study of the growth of silicalite-1 films on the seeded gold surfaces. - Studies in Surface Science and Catalysis, v.125, Eds: I.Kiricsi, G.Pal-Borbely,J.B. Nagy & H.G. Karge, Porous materials in environmentally friendly processes, 221.

22. Mihailova, B., V. Engstrom, J. Hedlund, A. Holmgren, J. Sterte. 1999. Vibrational Spectroscopy Study of the Structure of Silicalite-1 films on a gold Surface. - Microporous and Mesoporous Materials, 32, 297-304.

23. Mintova, S., V. Valtchev. 1999. Synthesis of nanosized FAU-type zeolite. - Studies in Surface Science and Catalysis, v.125, Eds.: I.Kiricsi, G. Pal-Borbely, J.B. Nagy & H.G. Karge, Porous materials in environmentally friendly processes, 221.

24. Mintova, S., N. Olson, T. Bein. 1999. Electron Microscopy Reveals the Nucleation Mechanism of Zeolite Y from Precursor Colloids. - Angewandte Chemie, 38/21, 3201.

25. Mintova, S., N. Olson, V. Valtchev, T. Bein. 1999. Mechanism of zeolite A nanocrystal growth from colloids at room temperature. - Science, 283, 958-960.

26. Mitov, S., I. Dontchev, D. Stoyanov, T. Blazeva, N. Lihareva. 1999. Geologic survey works in the tailings pond for calcium-arsenic sediments in the "MDK" ltd, Pirdop town. - In: Poc. of the nat.conf. "Protection and rehabilitation of environment in exploration, mining of mineral resources and metallurgy", Varna, 47-52 (in Bulgarian with English abstract).

27. Mitov, S., I. Dontchev, D. Stoyanov, V. Veleva, T. Blazeva. 1999. Geological researches of the clinker dump in unit 32040 and geochemical changes in the storied waste in qualitative and quantitative aspect. - In: Proc. of the nat.conf. "Protection and rehabilitation of environment in exploration, mining of mineral resources and metallurgy", Varna, 271-278 (in Bulgarian with English abstract).

28. Moliner, R., M. Lazaro, I. Suelves, C. Braekman-Danheux, S. Vassilev. 1999. NO_x reduction on coal chars doped with petroleum ashes. - In: Proceed. of the 10^thInter. Conf. on Coal Sci., B. Li and Z. Liu, eds., Sept. 12-17, 1999, Taiyan, Shanxi, China, v. II, 1513-1516.

29. Mouchovski, J., V. Genov, L. Pirgov, V. Penev. 1999. Preparation of CaF₂ precursors for laser grade crystal growth. - Mat. Res. Innovat., 3, 138-144. 30. Penev, V., L. Konstantinov, M. Marinov. 1999. Geometrization of the language of chemistry. Formulation of the problem. - Compt.rend.Acad. bulg.Sci., 52, 1-2, 49-52.

31. Petrov, St., J. Churtchev, R. Mitova, L. Boyanova, M. Tarassov. 1999. Xantoma of the stomach - some morphometrical peculiarity and scanning electron microscopy. - Hepato-Gastroenterology, 46, 1220-1222.

32. Petrova, R., T. Todorov, S. Bakardjieva, B. Mihailova, O. Angelova. 1999. Crystal structures of Cd(ReO₄)₂.4Urea, Cd(ReO4)₂.6Urea and Ca(ReO₄)₂.5Urea. Synthesis and characterization of urea aducts from the systems M(ReO₄)2-U-H₂O, M=Ca,Sr,Ba,Pb and Cd; U= urea. - Z. fur Kristallogr., 215, 1-4.

33. Stanimirova, Tz., N. Petrova. 1999. DTA and TG study of minerals from the hydrotalcite-takovite isomorphic series: II. Influence of M²⁺/M³⁺ cation ratio. - Compt. rend. Acad. bulg. Sci., 52, 11-12, 59-62.

34. Tarassov, M., N. Khaltakova. 1999. Acid alteration of scheelite: II. Using a fundamental building blocks approach to conversion of scheelite to WO₃.1/3H₂O. - Compt. rend. Acad. bulg. Sci., 52, 1-2, 61-64.

35. Tarasova, E. 1999. Native gold in metagranitoides of Belasitsa mountain. - Mining and Geology, 54, 10, 17-20 (in Bulgarian with English abstract).

36. Tarasova, E. 1999. Ni-Co-Fe sulphoarsenides and sulphides and their mineral parageneses from the Zvezdel-Pcheloyad ore district, Eastern Rhodopes. - Geochem., Mineral. and Petrol., 36, 137-147 (in Bulgarian with English abstract).

37. Tosheva, L., V. Valchev, J. Sterte. 1999. Bilayered hollow zeolite tubes. - In: Proc. 12^th Inter. Zeolite Conf., Mater. Res. Soc., 629-635.

38. Tosheva, L., V. Valtchev, J. Sterte. 1999. A method for the preparation of silicalite-1 microspheres. - Studies in Surface Science and Catalysis, v.125, Eds: I. Kiricsi, G. Pal-Borbely, J.B.Nagy & H.G. Karge, Porous materials in environmentally friendly proceses, 21.

39. Tsintsov, Z. 1999. Native gold extraction accompanying inert materials production in Bulgaria: experience and perspectives. - Mining and Geology, 54, 10, 14-17 (in Bulgarian with English abstract).

40. Tsintsov, Z. 1999. Sulphides of the PGE in the alluvial sediments of Blagoevgrad graben. - Compt. rend. Acad. bulg. Sci., 52, 1-2, 57-60.

41. Valtchev, V., J.-L. Paillaud, H. Kessler, E. J. Creyghton. 1999. Inductive effect of template-containing UTD-1 seeds on the synthesis of SSZ-24. - Microporous and Mesoporous Materials, 33, 143.

42. Valtchev, V., J.-L. Paillaud, S. Mintova, H. Kessler. 1999. Investigation of the ion exchanged forms of the microporous titanosilicate K₂TiSi₃O₉.H₂ O. - Microporous and Mesoporous Materials, 32, 287-296.

43. Vassilev S., C. Braekman-Danheux, P. Laurent. 1999. Characterization of refuse-derived char from municipal solid waste. 1. Phase-mineral and chemical composition. - Fuel Proc. Techn., 59, 95-134.

44. Vassilev, S., C. Braekman-Danheux, P. Laurent, T. Thiemann, A. Fontana. 1999. Behaviour, capture and inertization of some trace elements during combustion of refuse-derived char from munisipal solid waste. - Fuel, 78, 1131-1145.

45. Vassilev, S., C. Braekman-Danheux. 1999. Characterization of refuse-derived char from municipal solid waste. 2. Occurrence, abundance and source of trace elements. - Fuel Proc. Techn., 59, 135-161.

46. Vassilev, S., C. Braekman-Danheux, R. Moliner, I. Suelves. 1999. Characterization of coal chars impregnated with transition metals for low-cost catalytic NO_x reduction. - In: Proc. of the 10^thInter. Conf. on Coal Sci., B. Li and Z. Liu eds., Sept. 12-17, 1999, Taiyuan, Shanxi, China, v. II, 1517-1520.

47. Vitov, O. 1999. Geochemical features of soils along the trans-European coridor No 8, Dervena-Ranenci region, Kustendil district. - In: Proc. of the Society of nature preservation, 4, 27-40 (in Bulgarian).

48. Zotov, N., R. Miletich, H. Boysen, H. Tietze, W. Kockelmann. 1999. Copper substitution in (Cu,Mn)₇O₁₂ braunite: A combined neutron and X-ray powder diffraction study. - Material Science Forum, 321-324, 791-795.

49. Zotov, N., I. Ebbsjo, D. Timpel, H. Keppler. 1999. Calculation of Raman spectra and vibrational properties of silicate glasses: A comparison between Na₂Si₄O₉ and SiO₂ glasses. - Phys. Rev. B, 60, 6383-6397.

50. Zotov, N., M. Marinov, N. Mousseau, G. Barkema. 1999. Dependence of the vibrational spectra of amorphous silicon on the defect concentration and ring distribution. - J. of Physics: Condensed Matter., 11, 9647-9658.

51. Zotov, N., R. Delaplane. 1999. Structure and crystallization kinetics of sodium tetrasilicate glass: A high temperature neutron diffraction study. - Material Science Forum, 321-324, 535-539.

PUBLICATIONS IN PRESS:

52. Dimov, V., A. Ilieva, N. Khaltakova, L. Filizova. Structural model of Al₁₃-pillared montmorillonite. - Clays and Clay Minerals, 48, 1.

53. Engstrom, V., B. Mihailova, J. Hedlund, A. Holmgren, J. Sterte. The effect of seed size on the growth of silicalite-1 films on gold surfaces. - Microporous and Mesoporous Materials,

54. Kostov-Kytin, V. 1999. Structure proposal for a synthetic Pb-Sb-CI sulphosalt phase. - Compt. rend. Acad. bulg. Sci.,

55. Lihareva, N., P. Kosturkova, C. Vakarelska. 1999. Application of sodium carbonate-zinc oxide decomposition on mixture on ICP-AES determination of boron in tourmaline. - Fresenius J. Anal. Chem.,

56. Maleev, M.Chr., V. Kostov-Kytin. 1999. On the growth of the hexagonal prism on the crystals of a-quartz. Compt. rend. Acad. bul.Sci., 52, 9.

57. Petrov, O., E. Dyulgerova, L. Petrov, R. Popova. 1999. Characterization of calcium phosphates obtained during the preparation of sintered biphase Ca-P ceramics. - Materials Letters,

58. Schoeman, B., E. Babouchkina, S. Mintova, V. Valtchev, J. Sterte. The synthesis of discretecolloidal crystals of zeolite Beta and their application in the preparation of thin microporous films. - J. PorousMater.,

59. Shumov, D. Solvents in BaO-B₂O₃ system suitable for the growth of NdAl₃(BO₃)₄ crystals. - In: Intern.Conf. on Borate Glasses, Sofia,4-9.07.1999, Crystals & Melts, Eds. Y.B.Dimitriev and A.C.Wriht, Special Edition of Physics and Chemistry of Glasses.

60. Shumov, D. LiB₃0₅ single crystall growth and main growth defects. - In: Intern.Conf. on Borate Glasses, Sofia, 4-9.07.1999, Crystals & Melts, Eds. Y.B.Dimitriev and A.C.Wriht, Special Edition of Physics and Chemistry of Glasses.

61. Toneva, A., N. Petrova, S. Bakardjieva. 1999. Tribochemical method for obtaining of ecological compounded phosphate fertilizer. - Journal of Agricultural and Enviromental,

62. Tosheva, L., V. Valtchev, J. Sterte. Silicalite-1 containing microspheres prepared using share directing macro-templates. - Microporous and Mesoporous Materials,

63. Tsintsov, Z., A. Kunov. Silver mineralizations in chrysolite serpentinites from Eastern Rhodopes, Bulgaria. - N. Jb. Miner. Mh.,

64. Tsintsov, Z. Platinum-group minerals in sediments from Gotse Delchev graben, SW Bulgaria. - Compt. rend. Acad. bulg. Sci., 53, 2.

65. Valtchev, V., J.-L.Paillaud, T. Lefubvre, D. Le Nouen, H. Kessler. Synthesis and characterization of Mu-14^o: An aluminosilicate zeolite with the ITE-type topology. - Microporous and Mesoporous Materials,

66. Vassilev, S., G. Eskenazy, C. Vassileva. 1999. Contents, modes of occurrence and origin of chlorine and bromine in coal. - Fuel,

67. Vassilev, S., G. Eskenazy, C. Vassileva. 1999. Contents, modes of occurrence and behaviour of chlorine and bromine in combustion wastes from coal-fired power stations. - Fuel,

68. Vergilov, Z., V. Dimov, I. Vergilov. 1999. Pilot real structure modelling of Vitosha tourmaline. - Ann.Univ.Sofia, Livre 1 - Geol., 91 (in Bulgarian with English abstract),

69. Zidarov, N., J. Muchovski, M. Marinov, M. Tarassov, N. Zotov. Ion mass transport in anhydrous basaltic melts in electric field. - Chem. Geol.,

70. Zidarova, B., N. Zidarov. Basic elements of the geogenetic model of fluorite formation. III. The Ciprovci deposit. - Compt. rend. Acad. bulg. Sci., 53, 5,

71. Zotov, N., F. Bellido, M. Dominguez, A. Hannon, R. Sonntag. 1999. Continuous random network models of Cu-As-Te glasses. - Physica B,

72. Zotov, N., H. Keppler. 1999. In-situ Raman spectra of dissolved silica species in aqueous fluids to 900^o C and 14 kbar. - Amer. Miner.,

ABSTRACTS AND POSTERS AT SCIENTIFIC EVENTS:

73. Damyanov, Z., M. Vassileva. 1999. Layer silicates in the siderite ore from the Kremicovtsi deposit. - In: Proc. of "The problem of minerogenesis", Anniv. scient. session in honour of acad.I.Kostov, Sofia, 21-22.01.1999, 10 (in Bulgarian).

74. Dinolova, E., V. Ganev, L, Konstantinov.1999. UV-Vis Spectra of zeolitic K₂TiSi₃O₉. H2O-experiment and molecular orbital calculation. -In: Proc. of XIII conf.of glass and ceramic, Varna, 29.09. - 10.1999.

75. Dontchev, I. 1999. High-temperature alumina-bearing phases in ferroalloys slags. - In: Proc. of "The problem of minerogenesis", Anniv. scient. session in honour of acad. I. Kostov, Sofia, 21-22.01.1999, 12 (in Bulgarian).

76. Dontchev, I., A. Lenchev, L. Gigova. 1999. Investigations of fly ashes from the EPS "Dimitrovgrad" and experiments for receiving of ash-cement mixtures.. - In: Poc. of Sci. conf : "Completely utilization of mineral resources and industrial wastes in conditions of market economy", Sofia, 20.04.1999, 14 (in Bulgarian).

77. Dontchev, I., K. Mitov, V. Velitchkov. 1999. Possibilities to utilization of useful conponents of the waste weltz-clinker. - In: Proc. of Sci. conf. "Completely utilization of mineral resources and industrial wastes in conditions of market economy", Sofia, 20.04.1999, 8-9 (in Bulgarian).

78. Lihareva, N., K. Mitov. 1999. Chemical forms of arsenic and theirs distribution in the deposits of the tailings pond "Siniata laguna". - In: Proc. of Sci. conf. "Completely utilization of mineral resources and industrial wastes in conditions of market economy" Sofia, 20.04.1999, 29-30 (in Bulgarian).

79. Macheva, L. 1999. P-T history of rocks from the Byala Reka metamorphic group, Eastern Rhodopes (Bulgaria): chemistry and polytypism of white micas. - In: Abstracts of EUG-10, Strasbourg, 28.03-1.04.1999, 470.

80. Macheva, L. 1999. Potassium feldspars from metagranitoids of Byelorechka metamorphic group, Eastern Rhodopes - genesis and metamorphic evolution. - In: Proc. of "The problems of minerogenesis", Anniv. scient. session in honour of acad. I.Kostov, Sofia, 21-22.01.1999, 22 (in Bulgarian).

81. Nihtianova, D., V. Ganev, N. Khaltakova, M. Gospodinov. 1999. Crystal structure identification of Bi₂(MoO₄)₃ single crystals. - In: Proc. of Autunm School on Materials Sciences and Electron Microscopy, September,1999, Max Planck Inst.of Microstr. Physics, Halle, Germany.

82. Penev, V., N. Zidarov. 1999. Geometrization of the language of mineralogy: A forthcoming evoltionary stage of its development. - In: Proc. of the II Int. Mineralogical Seminar "History and Philosophy of Mineralogy" 4-8.10.1999, Syktyvkar, Russia , 26-29.

83. Shumov, D. 1999. Solvents in BaO-B₂O₃ system suitable for the growth of NdAl₃(BO₃)₄ crystals. - In: Proc. of the Intern.Conf. on Borate Glasses, Sofia, 4-9.07.1999, Crystals & Melts, Eds. Y.B.Dimitriev and A.C.Wriht, Special Edition of Physics and Chemistry of Glasses.

84. Shumov, D. 1999. Grouwth and growth defects of lithium triborate LiB₃0₅In: Proc. of the Intern.Conf. on Borate Glasses, Sofia, 4-9.07.1999, Crystals & Melts, Eds. Y.B.Dimitriev and A.C.Wriht, Special Edition of Physics and Chemistry of Glasses.

85. Vitov, O. 1999. Schlich-mineralogical mapping and prognosis for gold prospecting in Rila - Rhodopes area and Kraishte. - In: Proc. of III Nat. symp. "Metallogeny of Bulgaria", Sofia, 23-24.11.1999, 15-18 (in Bulgarian).

86. Vitov, O. 1999. Geochemical regioning and prognosis for prospecting of lead ores in Kamenitza depression, Kustendil district. - In: Proc. of III Nat. symp. "Metallogeny of Bulgaria", Sofia, 23-24.11.1999, 18-19 (in Bulgarian).

87. Vitov, O. 1999. Schlich-mineralogical map in ? 1:100 000 for solving metalogenic and ecologic ploblems. - In: Proc. of III Nat. symp. "Metallogeny of Bulgaria", Sofia, 23-24.11.1999, 19-21 (in Bulgarian).

88. Vitov, O. 1999. Thermotransfusion of gold in the wall of furnace for black copper melting. - In: Proc. of III Nat. symp. "Metallogeny of Bulgaria", Sofia, 23-24.11.1999, 22-24 (in Bulgarian).

89. Zelyazkova-Panayotova, M., Z. Tsintzov, G. Pashov. 1999. Hydrothermal gold mineralizations in ultrabasits near village of Dobromirtzi, Kardjali district - In: Proc. of III Nat. symp. "Metallogeny of Bulgaria" , Sofia, 23-24.11.1999, 47-50 (in Bulgarian).

90. Zidarov, N., J. Muchovski, M. Marinov, M. Tarassov, N. Zotov. 1999. Mass transport in anhydrous basaltic melts in electric field. - VI^th Silicate Melt Workshop, France, 13-17.04.1999.

PUBLICATIONS AND REPORTS NOT INCLUDED IN THE PREVIOUS ANNUAL REPORTS OF CLMC

1995

1. Angelova, O., J. Macicek, R. Petrova, T. Todorov, B. Mihailova.1995. Structures of molecular adducts of inorganic salts. V. Compareson of Cd (ReO₄)₂.2 Urea and Cd(ReO₄)₂.2H₂O. - Z. f?r Krystallogr. 210, 24-30.

2. Donchev, I. 1995. Technological mineralogy in the conditions of transition to market economy. - Geol. and miner. resources, 2-3, 26-29 (in Bulgarian with English abstract).

3. Donchev, I., Chr. Stantchev. 1995. The distribution of non-ferrous metals and arsenic containing phases in the slags of MDK Inc. Pirdop. - J. of Mining and Geol., 4, 33-37 (in Bulgarian with English abstract).

4. Kaltchev, M., A. Andreev, N. Zotov. 1995. Water-glas Shift reaction on CuO/ZnO catalysts I. Structure and catalitic activity. - Kinetics and Katalys, 36, 821-827.

5. Kamenov, B., E. Tarassova. 1995. The Polskigradetz pluton from Eastern Bulgaria - petrology, geochemistry and ore mineralizations. - Proc. of the XV congress of KGBA, Athens, Greece,No 4/2, 527-532.

6. Lazarova, V., S. Mintova, V. Valchev. 1995. Influence of zeolite fillers on optical and physical properties of pigment coated paper. - Compt. rend. Acad. bulg. Sci., 48, 10, 71-74.

7. Lazarova, V., S. Mintova, V. Valchev. 1995. Influence of zeolite flocculation in paper on its optical characteristics. - Bulg. Chem. Commun., 28, 2, 276.

8. Macicek, J., O. Angelova, R. Petrova.1995. Structures of molecular adducts of inorganic salts.I. Pb(ReO₄)₂.Urea.H₂O and Ba (ReO₄)₂.3Urea. - Z. f?r Krystallogr., 210, 24-30.

9. Macicek, J., O. Angelova, R. Petrova.1995. Structures of molecular adducts of inorganic salts. II. Ca(ReO₄)₂.Urea.H₂O. - Z. fur Krystallogr. 210, 319-322.

10. Radev, D., V. Blaskov, I. Mitov, A. Toneva. 1995. Influence of mechanochemical activation on the solid state synthesis of ferri molibdate. - Balkan Science-technological Conference, Proc. Contact'95, 88-94.

11. Valtchev, V., S. Mintova. 1995. The role of surface metal imperfections of the zeolite film formation. - Proc. of the East-West Surface Science Workshop, 14-21 February, 1994, Eds. M.Mihailov and I.Gutzov, 295.

12. Valtchev, V., S. Mintova, D. Radev. 1995. Synthesis of Zeolite Thin Films on Metal Plates. - Proc. of the East-West Surface Workshop, 14-21 February 1994, Eds. M.Mihailov and I.Gutzov, 291.

1996

1. Ivanov, I., D. Nihtianova, I. Georgieva. 1996. X-ray powder diffraction and transmission electron diffraction data for BaMnSi₂O₆ - A new phase in the system BaO-MnO-SiO₂. - Powder Diffraction, v.II, No4, 284-287.

2. Kostov-Kytin, V. 1996. Blok-building principles in the structures of some leadantimony chlorine sulphosalts. - Compt.rend.Acad.bulg.Sci., 50, 5, 55-58.

3. Marinova, I., O. Vitov. 1996. Geochemical zonation and prospects for mineral resources in the Bosnek-Gorna Dikanya-Dren area, Radomir district (West Srednogorie). - Rev.Bulg.Geol.Soc., 57, 3, 21-30.

4. Nihtianova, D., D. Shumov, J.J. Macicek, A. Nenov. 1996. Inclusions in LiB₃O₅ crystals obtained by the top-seeded solution growth method in the Li₂O-B₂O₃ system. Part 2 - J. of Cryst. Growth, 169, 527-533.

5. Shumov, D., A. Nenov, D. Nihtianova. 1996. Inclusions in LiB₃O₅ crystals obtained by the top-seeded solution growth method in the Li₂O₃-B₂O₅ . Part I. - J. of Cryst. Growth., 169, 519-526.

6. Yanev Y., N. Zotov. 1996. Infrared spectra of water in volcanic glasses. - Experiment in Geosciences, 5, 1-9.

1997

1. Breskovska, V., V. Kostov-Kytin. 1997. Native elements and intermetal compositions - new finds for Bulgaria. - Compt.rend.Acad.bulg.Sci., 50, 9-10, 63-66.

2. Ignatova, K., L. Nikolova, V. Dimov. 1997. Structure of electrolytically deposited Pd-Ag powders. - J.Phys.Chem., B, 101, 6891-6894.

3. Lihareva, N., M. Delaloye. 1997. Determination of Hf, Sc and Y in geological samples together with the REE. - Fresenius J. Anal. Chem., 357, 314-316.

4. Lilkov, V., O. Petrov. 1997. Hydration of cement mixed with "Pozzolite" mineral additive. - Proc. 10th Int.Congress Chem. Cement: Additives, Admixture, Characterization Techniques, ed. Harald Justnes, Gotheburg, Sweden, June 2-6, 3ii1167.

5. Tarassova E., Z. Iliev, R. Iliev. 1997. Placer alluvial gold from the Malkoturnovo ore field. - 50th Univers.geol., Ann. Univ. Sofia, 47-50 (in Bulgarian).

6. Zotov, N., F.Bellido, R. Jimenez-Garay 1997. Structure of Ag-As-Se glasses with high silver content - X-ray diffraction and Reverse Monte Carlo Simulations. - J. Non Cryst. Solids, 209, 149-158.

1998

1. Deganello, G. Liota, L. Longo, A. Martorana, Y. Yanev, N. Zotov. 1998. Structure of natural water-containing glasses from Lipari (Italy) and Eastern Rhodopes (Bulgaria) - SAXS, WAXS and IR studies. J.Non-Crystalline Solids, 232-234, 547-553.

2. Deneva S., V. Dimov, V. Kapurdov, K. Kamchev, R. Goranova, M. Kostova. 1998. On the evaluation of ambient air asbestos pollution near an industrial source. - Centr.Eur.J. of Occup. And Envir.Med., 4(4), 372-375.

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