BULGARIAN ACADEMY OF SCIENCES

 

CENTRAL LABORATORY
OF MINERALOGY AND CRYSTALLOGRAPHY

ANNUAL REPORT
No 1/1995

 

Editor: Dr. Nikola Zidarov; E-mail: nzidarov@interbgc.com
© Central Laboratory of Mineralogy and Crystallography, 1996
ISSN 3033-2206

CONTENTS

Projects No 6, 12, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 30, 31, are financially supported in part by the Bulgarian National Science Fund, while project No 27, in addition, by the International Centre for Diffraction Data (ICDD-JCPDS), USA

INTRODUCTION

On the 1st of March, 1995, was initiated the Resolution of the 72-nd session of the General Assembly of the Bulgarian Academy of Sciences (BAS) for creation of a Central Laboratory of Mineralogy and Crystallography (CLMC) which obtained the status of a juridical institution with own bank account and balance and with a field of activity: fundamental and applied scientific research; consulting, expertise, service and analytical activity; utilization of scientific results; and training of highly qualified specialists in the fields of mineralogy and crystallography; study and modeling of natural and technogenic mineral systems".

This Resolution came as a result of the "Conception for reorganization of BAS". Its preparation is a merit of the Constitutive Council of CLMC, which on the base of the international and national priorities in the field and taking into account the qualification of the researchers and the material basis of the former Institute of Applied Mineralogy prepared and defended a conception about the structure, staff, and the scientific fields to be developed by CLMC.

On the 8th of March, 1995, on its session the Governing Council of BAS, basing on the submitted proposals confirmed the staff and the structure of CLMC to consist of three scientific departments - Topographic mineralogy, Experimental mineralogy and crystallography, and Structural crystallography, as well as of one Service laboratory sector.

The present annual report covers the activity of CLMC during the first year of its functioning.

The most important scientific results, a part of which being published or reported on scientific conferences can be grouped as follows:

  • The first geogenetic models for the mineral formation processes in representative deposits of the fluorite formation are created as a result of determination of the type, character, and spatial distribution of the inhomogeneities in a row of minerals and mineral bodies; determined are the thermal barometric conditions for formation and metamorphic evolution of protoliths from a subducted ophiolite fragment in Ograzden mountain; determined is the phase composition and the distribution of the platinum group minerals in sediments of the Blagoevgrad graben; identified and characterized are new minerals for some Bulgarian deposits including all representatives of the heulandite-clinoptilolite row in zeolite rocks from Eastern Rhodopes; silver-copper alloy in natural formations from the oceanic rift zone is established foe the first time.
  • Determined are the crystal structures of 20 newly synthesized phases of simple and double selenates, selenites, and adducts of inorganic salts with organic molecules, Cl-containing sulphosalts; the structure and crystallization kinetics of the microporous silicates, ETS-4, ETS-10, and SAPO-5, are determined.
  • The results from studies on the mineralogy and geochemistry of coals and coal ashes from 42 deposits from around the world are summarized and the relations between mineral and chemical composition of coal determined as well as their melting, degree of coalification and ash content.
  • On the bases of cluster modeling of Raman and infrared spectra of crystals and amorphous media are determined the structures and thermodynamic parameters of silicates and meta-silicate glasses, heterophases systems, as well as the influence of various types of disorder and alterations taking place during phase transition from ordered to disordered state.

Most important among the applied scientific achievements are:

  • Worked out is a complex of mineral-geological criterions for prospecting of stratiform polymetal-barite-iron ore deposits in Sredets ore region.
  • Submitted are 2 patent requests about new methods for preparation of zeolite-containing complex materials and for their use as filters, sorbents, and catalysts.
  • A tunable TeO2 acousto-optical filter in the visible spectral region is designed.

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

  • Synthesis and structural characterization of palladium catalysts supported on volcanic glasses from the island of Lipari (Italy) and from the Eastern Rhodopes mountains (Bulgaria). A collaboration with ICTPN-CNR (Instituto di Chimica e Technologia dei Prodotti Naturali del CNR via Archirafi), Palermo, Italy;
  • Spectroscopic and thermochemical studies of silicate glasses, Cd-Si-oxide pollyphase ceramics and new materials. A collaboration with Institute of Ceramic and Glass, Madrid, Spain;
  • X-ray diffraction of miscellaneous phases. A collaboration with International Centre for Diffraction Data (ICDD-JCPDS), USA.
In this annual report the researchers of the Laboratory summarize the results of their research work, emphasizing on papers either published or accepted for publication as well as on communications reported at scientific conferences and symposia.

The research themes are consistent with the scientific topics to be developed in the next years. The themes are to a great extent specified by the researchers and the accepted ones are financed by BAS, while those having won competitions are supported financially in addition by the Bulgarian National Science Fund of the Ministry of Education, Science and Technologies.

In this first annual report we announce our ideas on the problems to be studied as a starting point in the field of mineralogy and crystallography as well as information is provided about the staff's scientific competence and potential.

We hope this issue to allow us new contacts and collaboration with other research teams and institutes working in the field.
 

Nikola Zidarov
Sofia, January 1996

RESEARCH TOPICS:

I. MINERAL SYSTEMS:

1. Phase and chemical inhomogeneities in Bulgarian fluorite deposits.
(B. Zidarova, N. Zidarov)

Phase and chemical inhomogeneities in fluorite crystals, aggregates and bodies in the main Bulgarian fluorite deposits of industrial interest, Mikhalkovo in the Rhodopian massif and Slavyanka in the Serbo-Macedonian massif, are investigated from genetical viewpoint. Both deposits belong to the hydrothermal Fluorite Formation - the former being of stratiform, while the latter of vein type. The morphology and structure of the bodies, as well as the horizontal layering of aggregates, discordant with that of the marble layers, suggest a sedimentary gravitational mechanism of the formation of some fluorite bodies in Mikhalkovo deposit [50].

In order to find the changes in temperature and composition of the mineral - forming fluids the temperature of homogenization and the composition of fluid inclusions in various mineralogical types of fluorite in Slavyanka deposit were studied. A total reconstruction of the temperature regime of the fluorite formation was done. The type of transport of various compounds in the solutions depends mainly on their temperature, pH - factor and concentration [49]. The temperatures of homogenization and formation of the phases were determined by studying the fluid inclusions in synthetic fluorites, crystallized in an autoclave at P=100-120 MPa and T=340-464 °C in NH4Cl and LiCl solutions (7-44,6%). The changes in the initial vacuoles volume cause homogenization of the iclusions which takes place at temperatures substantially higher than that estimated from P-T-X data. This temperature of synthesis is even higher than that of the fluorite crystallization [23].

The type and the distribution of the chemical inhomogeneity in fluorites from various hypsometric levels of Slavyanka deposit have been studied by laser microspectroscopy, microphotometry of the optical density, and by subsequent mathematical processing. The impurities influence the variations in the optical

density, determining the complicated fluctuations which correspond to macro- and micro- zonality. The information obtained makes it possible to study the dynamics of the parameter variations during every stage of the fluorite formation [47].

The change in the relative concentration of the end- members of the series La-Lu is most marked in fluorites. The atomic ratios, Tb/Ca and Tb/La, can be used to draw genetic conclusions. The distribution of La and Tb in hydrothermal fluorite from Slavyanka deposit is indicative of the processes of rearrangement and redeposition [48].

In the local geogenetic models of Slavyanka and Mikhalkovo deposits the dynamics of hydrothermal fluorite formation is reconstructed as a function of the parameters of specific geologic situation and the fluorite formation mechanism [51-53].

2. Type, characteristics and spatial distribution of inhomogeneities in metamorphosed basic and ultrabasic rocks (N. Zidarov, P. Nenova)

Partially metamorphosed protoliths of serpentinized peridotites and/or harzburgites, spinel pyroxenites with clinopyroxene megacrysts, olivine gabbro-norite crossed by aphyric gabbro-noritic dykes and leucocratic gabbro together with eclogites and amphibolites, crop out as macroblocks and bodies in a frame of metaophiolitic melange body, included in two-mica gneiss-schist sequence of the metamorphic basement of the Ograzdenian Supergroup of the Serbo-Macedonian Massif, SW Bulgaria.

This body is considered as a system of three hierarchical levels: mineral individuals - mineral associations - mineral (lithologic) bodies. Phase, structural, and chemical inhomogeneities in this system are investigated. On the mineral individuals level these concern the main rock forming minerals, i.e. pyroxenes, olivines, garnets, plagioclases, amphiboles, spinels, etc. The phase transition of coesite - to - quartz (pseudomorph) was observed in kyanite eclogites [46].

On the mineral association level, distinguished are the equilibrium phase relations for both magmatic protoliths and the products of their metamorphic transformation. According to thermobarometric data for relict mineral associations and their structural relations the PT- conditions of protolith formation and PT-path of its metamorphic evolution during the five main stages are defined: M1 - granulitization, M2 - prograde eclogitization, M3 - UHP-metamorphism, M4 - retrograde eclogitization, M5 - multiphase amphibolitization.

On the lithological bodies level, the ophiolite rock association is considered as a part of dismembered oceanic crust. Gabbros and pyroxenites are formed under PT conditions of the Upper Mantle. The UHP/HT conditions (1020 - 1150 °C, 22 - 30 kbar) are characteristic of the peak metamorphism stage ( M3 ), which is related to subduction or collision events [45].

3. Inhomogeneity in the platinum-group minerals from placers of SW Bulgaria (Z. Tsintsov, L. Petrov)

Platinum-group minerals (PGM) and the silicate inclusions therein, obtained from alluvial sediments of Blagoevgrad graben are investigated. The phase composition and characteristics of silicates observed in the matrix of individual grains of PGM were determined [78]. The grains consist of olivine, augite, gedrite, taramite, phlogopite, plagioclase and one of the mineral species of Al2SiO5 - and are sized from 3-5 to 18-20 mm and irregularly shaped. The grains of augite are very rarely observed with crystal walls in contrast to the sperrylite, Pt-Fe alloys and PGE alloys. One Pt-Fe alloy grain was found to contain silicate-glass inclusions with almoust perfect spherical shape and sized from 5 to 15 mm.

The mineral features of the Pt-Fe alloy crystals were studied, the data showing that these are samples of native platinum and isoferroplatinum. They are presented by simple forms of octahedron (18.6%) and cube (25.6%), and combinations (55.8%) of the (100), (111) and (110) faces. The studied single grains of laurite-erlichmanite series have massive homogeneous surface and are composed by intermediate members in which the elements are uniformly distributed and inclusions of other phases were not established.

4. A mineralogical map scaled 1:25 000 of the heavy mineral concentrates in Bulgarian stream sediments. (O.Vitov)

New method, software and technology were developed for processing mineralogical data concerned with the sampling of heavy mineral concentrates in stream sediments collected all over Bulgaria [42]. A data-base of 120 000 samples (about a tenth of the total amount of samples in Bulgaria) was created, and on its basis a map (1:25 000) is in preparation. The work aims at:

1. Estimation of the completeness and the quality of sampling.

2. Specification and distribution of areas of uniform set of heavy mineral concentrates in stream sediments for metallogenic analyses.

3. Identification of new areas for prospecting mineral resources.

A zonal distribution of heavy mineral concentrates in stream sediments from Eastern Rhodope Massif was observed. On the basis of mathematical modeling it was proved that NW-SE and NE-SW faults play an important role for the distribution of minerals and mineral associations in the area. As a result, an exploration prognosis and evaluation of the ore potential for the region were carried out [41].

5. Sedimentary-hydrothermal ore formation: products, processes, ore-forming models (Z. Damyanov)

New data on the mineralogy, geochemistry and geology were found for the primary ores from the Kremikovtsi carbonate-hosted submarine exhalative iron (+Mn)-barite+(base metals) deposit, West Balkan, Bulgaria [1-3, 58]. Several major mineral parageneses and geochemical associations in the iron carbonate ores were distinguished [24]. The lateral and vertical ore zoning as well as the classification affiliations of the deposit were also elucidated [58]. The leading role of the sedimentary-hydrothermal processes for the Kremikovtsi deposit formation was established. Similar genetic and time-spatial relations of the iron(+Mn) and barite(+base metals) ore types were proved. A new submarine exhalative model of ore formation was proposed for the Kremikovtsi deposit [3, 5, 58]. Paleogeographic and tectono-magmatic factors controlling the ore formation were analyzed in detail. Favorable prerequisites for prospecting of new ore bodies and deposits from the same ore type were pointed out. Criteria for exploration of stratiform and strata-bound iron-barite-polymetallic deposits in perspective areas of the Sredec ore region (central parts of Western Bulgaria) were also proposed [4].

6. Mineralogical studies of native metals and alloys from the oceanic rift zones (East Pacific Rise, 21° S and Mid-Atlantic Ridge, 26° N - TAG hydrothermal field) (V. Dekov, Z. Damyanov)

About 550 representative samples from the East Pacific Rise metalliferous sediments were inspected to find and to diagnosticate mineralogically 130 metallic particles, 16 of which were examined in detail by XRD, SEM, EPMA and OM. A hitherto unknown native silver-copper alloy was established; native aluminium, native tin and tin-lead alloys were also studied. Characteristics supporting the natural origin of the metals and alloys mentioned above were found. An endogenous model for their formation, related to the mantle evolution of magmatic systems under the strongly reducing conditions at the time of supposed stage of metallization of the silicate melt was proposed. As a result of the cyclic tectono-magmatic processes in the rift zones, host basic and ultrabasic rocks have probably undergone degradation and disintegration and the hyaloclastic material, including accessory metal particles, had been dispersed into the near-axial metalliferous sediments.

7. Mineralogical characterization and formation conditions of lead phosphate and sulphate-phosphate minerals from Brussevtzi Pb-Zn deposit, East Rhodope massif, Bulgaria. (Y. Tzvetanova)

In the frame of the oxidized zone of Brussevtzi deposit corkite, plumbogummite, plumbojarosite and iodargyrite in quartz-adularia type metasomatic rocks were established for the first time. The lead phosphates, corkite, plumbogummite and pyromorphite were characterized mineralogically in detail [28]. The crystal chemical formula and the unit cell parameters of these minerals were calculated. Corkite and plumbogummite form replacement- and incrustation pseudomorphs after pyromorphite and other mineral phases.

According to the chemical composition two varieties of corkite were distinguished: one with higher content of CuO and lower of P2O5, and another one with lower content of CuO and higher of P2O5. The SO3 content of the former is considerably higher than that of the later. This fact can be explained in terms of the general formula AB3(XO4)2(OH)6, where the isomorphous substitution of Fe3+, by Cu2+ in the B sites is accompanied by exchange of (PO4)3- by (SO4)2- in (XO4) sites to retain charge balance. The sequence in the formation of the secondary lead phosphates in Brussevtzi deposit is: pyromorphite-plumbogummite-corkite. The observed crystallization range suggests a decrease of Pb and P concentrations and a change of the pH-factor from acidic to alkaline in the solutions during the process of mineral formation.

8. Mineralogy, geochemistry, and formation conditions of skarns in Zvezdel-Pcheloyad Pb-Zn ore deposit, East Rhodope massif, Bulgaria.
(Y. Tzvetanova)

Preliminary data on a skarn body hosted in propilitised monzonites were collected. The established skarn minerals are: plagioclase (andesine-labradorite), pyroxene from the diopside-hedenbergite range, garnets , wollastonite, scapolite, titanite, apatite and magnetite. X-ray data and the unit cell parameters of garnets from different skarn zones show the presence of two varieties of garnets from the grossular-andradite range: with 80-92% and 44-56 mol % Ca3Al2Si3O12. A zonal distribution of the skarn minerals was observed. The following minerals were found to be formed during the late-stage hydrothermal processes: amphibole, epidote, quartz, calcite, chlorite, prehnite, sericite, and stilbite.

Based on studies of the mineral assemblages, the structure of the skarn zones, the relationship between different metasomatic processes and the estimation of mass transfer one can specify the skarns in Zvezdel-Pcheloyad intrusion as diffusive. They have been formed under conditions of high temperatures and normal alkalinity in long periods. The skarn facies is of a pyroxene-garnet-plagioclase type. The skarns are formed possibly by the substitution of xenolith of carbonate rocks belonging to the metamorphic complex.

9. Polyphase nature of heulandite-clinoptilolite in zeolite rocks from Eastern Rhodopes, Bulgaria. (O. Petrov)

Still, given the large amount of information on heulandite (Heu) and clinoptilolite (Cli), there have been no studies on the possibility of the existence of zeolitic rocks with multiple Heu-Cli compositions and resultant bimodal thermal behavior.

A more complex thermal response of the Heu-Cli group zeolites in sedimentary rocks from Eastern Rhodopes subjected to thermal treatment was distinguished by profile-fitting analysis of diffraction lines. The profile-fitting of 020 peak of initial and heated samples showed peak broadening with temperature which can be attributed to presence of more than one Heu-Cli group phases which contract differently and the more contracted one(s) is reason for this broadening. In some cases the profile attains a specific shape even reaching a distinct splitting which allowed several peaks with close d-spacings to be resolved and the registered for the first time d-spacings of 8.23 ? and 8.465 ? samples (heated at 750 °C) are related to the formation of contracted Cli B phase. A gradual intensity loss was registered as well, markedly expressed at temperatures below 400 °C which indicates presence of Heu and Ca-Heu.

The obtained preliminary results show that the studied Heu-Cli samples from Beli plast deposit in Eastern Rhodopes have a polyphase zeolite nature. The presence of Heu and high-silica Heu was proved for the first time in addition to the common Ca-Cli and Cli. Ca-Cli dominates in the samples.

10. Physicochemical and structural transformation of tungsten-bearing minerals under supergene conditions (M. Tarassov, V. Dimov,
N. Khaltakova )

Natural CaWO4 is treated by H2SO4 solutions (pH ~ 0.5-2.2) in order to elucidate the mechanism of scheelite alteration under supergene conditions. It was found that the decomposition of CaWO4 giving rise to WO3.2H2O and WO3.H2O as ultimate product passes through the formation of an intermediate phase WO3.1/3H2O [25]. TEM study gives evidence that WO3.1/3H2O is formed as result of two processes: 1) selective leaching of Ca from the CaWO4 structure which seems to be Ca2+/H+ ion exchange, and 2) transformation of the residual tungsten-oxygen skeleton into the new phase. Similar structural fragments as deformed six-membered rings of WO4 tetrahedra in CaWO4 and of apex-connected WO6 and WO5OH2 octahedra in WO3.1/3H2O facilitate this phase transformation. It was shown that the transition from WO4 tetrahedra to WO6 octahedra in the rings can occur through small atom displacement. The presence of additional ions (Fe2+, Fe3+) in the experimental solutions stabilize the structure of WO3.1/3H2O. It was observed that the crystallinity of WO3.1/3H2O decreases with decreasing the temperature and with increasing of the iron content in the solutions. This suggests that WO3.1/3H2O in the supergene zone could be observed only as poorly crystallized materials. A marked example is the recently described X-ray amorphouse ochre from the Grantcharitza deposit (West Rhodopes, Bulgaria).

11. TEM study and structural model of alumina-pillared montmorillonite (V. Dimov, N. Khaltakova, A. Ilieva, L. Filizova)

Alumina-pillared montmorillonite prepared by intercalation of polyoxy-hydroxy aluminum cations (Al137+) in the interlayer spacings of a natural montmorillonite from the Dimitrovgrad bentonite was studied. A structural model of the Al-O-props and their mutual disposition according to the clay matrix was proposed. Theoretical diffraction patterns in the coordinate axes directions of the modelled structure were derived, using a computer stimulation according to the known Multi-Slice method. In the same manner and for the same conditions, theoretical electronograms of the hypothetical montmorillonite structure with interlayer cation vacancies and an increased interlayer spacing corresponding to a d001 value of 17 ?, were also derived. TEM diffraction patterns in the c-direction of the pillared montmorillonite were experimentally obtained. On the basis of the good correlation between the above mentioned two types of theoretical electronograms and also comparing their agreement with the experimental data, the model was proved. Thus, by means of the proposed structural model, both the porosity and c-direction stacking sequence order of the pillared montmorillonite were explained.

12. Mineralogy and genesis of platinum-group elements and gold associations in porphyry cooper deposits and placers. (P. Dragov,
Z. Tsintsov)

The phase composition of PGM from the alluvial sediments of the Blagoevgrad graben was established and preliminary data was obtained on native platinum, isoferroplatinum, iridium, ruthenium, osmium, rutheniridosmine, mertieite II, braggite, cooperite, bowieite, kashinite, cuprorhodsite, sperrylite, laurite, erlichmanite, irarsite and hollingwortite.

II. TECHNOGENIC MINERAL SYSTEMS:

13. Mineralogy and geochemistry of coals and their products (S. Vassilev,
C. Vassileva).

As a result of this project have been characterized: the influence of mineral and chemical composition of coal ashes worldwide on their fusibility [37,38]; the relationships between coal rank/ash content and mineral and chemical composition of coals worldwide; the mineralogy and geochemistry of a vitrain lens with unique trace element content from the Vulche Pole coal deposit, Bulgaria [36]; the stack emissions from coal-fired power stations as an environmental pollution with trace elements [35]; the petrographical, mineralogical and chemical composition of Bobov Dol coals and their waste products from the coal-tretment plant and thermo-electric power plant [34,39,44]; the effective use of mineral sorbents for purification of contaminated waste waters from thermo-electric power stations [81].

14. Phase-mineralogical and chemical transformations and interactions in inorganic matter of coal during heating (S. Vassilev, C. Vassileva).

The study is in opening stage. The subject of the present project is the behaviour of the inorganic matter in coal during heating, as well as the mechanism of new-phase formations from organic and inorganic coal matter [37]. The phase-mineralogical and chemical transformations and interactions in inorganic matter of Bulgarian coals during their gradual heating will be systematized. The results will have a theoretical significance for: the behaviour of minerals and organic matter in coal during heating up to their ash-fusion temperatures; and the elucidation of the mechanism for inorganic products formation during coal burning. The obteined information will be of practical importance for: prediction and improvement of the technological process in coal-fired power stations by solving the problems, associated with the fuel quality and combustion technology; new effective use of the coal waste products; improvement of the environment in the areas surrounding the power plants.

15.Content and modes of chlorine occurrence in Bulgarian coals and their products (G. Eskenazi, S. Vassilev).

The study is in opening stage. The subjects of the present project are: the investigations on contents and geochemical features of chlorine distributions in some Bulgarian coal deposits; the relationships between chlorine concentrations and ash contents, coal rank, maceral components, correlation trends with other elements; the studies on modes of chlorine occurrence in coal and their origin; the behaviour of chlorine during coal burning; the prognosis for possible chlorine environmental contaminations in the areas surrounding the power stations.

III. SYNTHESIS AND CRYSTALLIZATION OF MINERALS AND MATERIALS:

16. Synthesis of chlorine sulphosalts and study of their crystal chemistry and properties (V. V. Kostov)

Several occurences of natural Cl-containing Pb-Sb sulphosalts inspired series of dry and hydrothermal syntheses to obtain some of them. PbS, Sb2S3 and PbCl2 were mostly used as starting materials. Preferred growth techniques were those from melt and reaction with gaseous transport yielding as run-products sulphosalt samples appropriate for further single crystal investigations. At least three or four Cl-containing Pb-Sb sulphosalts were obtained [10,11]. The chlorine content for different phases varies from 1.5 to 4.5 wt %. Hydrothermal syntheses were mainly conducted in silica-glass tubes inserted in steel autoclaves. Run products were Cl-containing (up to 5.5 wt %) sulphosalt phases represented by tiny little acicular crystals or their aggregates. Unfortunately, they are not appropriate for single crystal investigations. Further acquirement and improvement of this technique aiming at synthesis of crystals with better qualities are now in progress.

Confirmation of phase homogeneity and detection of the chlorine content was achieved by means of microscopic reflected light, X-ray powder diffraction and electron microprobe techniques. Further, appropriate samples were investigated by a CAD-4 diffractometer. Successful structure solutions were found for two of the phases. For one of them, Pb12.65Sb11.35S28.35 Cl2.65, the single crystal investigations revealed the space group I2/m, a=19.502, b=4.049, c=35.115?. Its crystal structure is closely related to that of dadsonite [12]. The structural characteristics of the other phase are the same as those of the already known synthetic phase Pb4Sb4S11 - Pbam, a=15.01, b=15.56, c=4.068 ?, but the content of Cl exceeds 4 wt %. Some chlorine atoms entirely occupy special positions and other partially substitute sulphur in the investigated structures. Apparently, chlorine is an essential component for the formation of some specific lead-antymony sulphosalts and its structure controlling role needs further investigation.

17. Hydrothermal synthesis of iron sulphides (G. K. Kirov)

The hydrothermal syntesis of iron sulphides is realized by means of a specially devised original method: partially open plastic, glass or quartz-glass tubes closed into an unlined autoclave; the tube contains the reacting solid and solution; the filling of the tube is a little bit higher than that of the autoclave with pure water in order to prevent from solution mixing. Starting from elementary iron and sulphur or from various salts and sulphides or sulphates of iron and solutions of alkaline chlorides synthesized were pyrite, marcasite and pyrothine in the temperature range 150 °C to 350 °C for fillings between 55 and 85 %. Investigations on the stability fields of the different phases and tne crystals habits are now in progress.

18. Etch pits on natural and man-made quartz crystals in different etching conditions (G. K. Kirov, M. Chr. Maleev)

Etch patterns on the main crystal faces ( r, z, m, x, a, `a, s, `s and c) and break surfaces of several hundred natural and man-made quartz crystals produced throught etching in HF, NH4HF2, NaOH, KOH, Na2CO3, K2CO3 and NaHCO3 under normal conditions, and at elevated temperatures and pressures were studied and discussed. The characteristic etch pit forms and contours were determined for each of the crystal face and set of etching conditions. Common for all the etch pits on all the crystal faces is their contours never being paralell to the main crystallographic directions, yet deviating a little bit from them in the left-handed and right-handed crystals. Several communications on the subject are in advanced stage of preparation.

19. Hydrothermal growth of man-made corundum crystals (M. Chr. Maleev)

Corundum crystals were grown hydrothermally in 150 ml unlined steel autoclaves [66]. The growth of corundum crystals on seed plates cut from melt-grown corundum was carried out in 1 or 1.5 mol Na and K bicarbonate solutions with certain quantity of NaCl added to reduce the pressure. The typical growth conditions were as follows: growing temperature around 500 °C and presssure between 140 to 180 MPa. Crushed melt-grown corundum, electrocorundum, corundum ceramics and metal aluminium were used as a nutrient and the best results were obtained with crushed crystals and metal aluminium. Crystals up to 5 cm and 10g were grown. The crystals were usually heavy coloured and muddy due to the Fe caught during its growth. Crystals grown in open copper liner were more transparent and contained a number of included small copper crystals. The growth rates and parameters of the main crystal faces were investigated.

20. New purification metod for growing laser-grade CaF2 crystals
(J. Mouchovski, V. Penev)

The growth of laser-grade CaF2 crystals is performed nowadays using high-cost, extremly pure CaF2 (99.99%). It is thought that mineral fluoshpar can not be concentrated to such a high degree due to the presence of rare-earth ions embeded isomorfically in the fluorite lattice as well as of noticeable amounts of deeply -sorbed oxygen contaminants. The work aims at obtaining highy purified precursors using Bulgarian raw material for growing laser-grade CaF2 crystals [73]. For the purpose an original method was developed in order to concentrate grained optical-quality fluorspar previously treated by the conventional chemical purification technique. The method consists of a high temperature (up to 1100 °C) treatment under low preassures (below 0.01 Pa) of the grained material mixed with PbF2 (1.5%) in a specially designed multi-camera crucible, which controls efficiently the speed of the vaporization, the mass transfer and the sublimation processes and, thus, separates the precursor into two parts, one highly purified from and another one, rich in rare-earth elements. Besides, both parts are effectively purified from oxygen contaminants the majority of which react with the PbF2 vapour at about 900 °C while the remainder desorbs at higher temperatures and is removed by the vacuum system. The highly purified precursors produced that way were used for in-group growth of cylinders by the Bridgman-Stockbarger method. The optical characteristics of the grown crystals were used for analyzing the mass and the heat transport processes during the purification procedure. The results obtained point to the way for further optimization of the method for industrial applications as an alternative technique for the production of laser-grade CaF2 crystals.

21. Inclusions in LiB3O5 single crystals obtained by TSSG method in the Li2O-B2O3 system. (D. Shumov, D. Nihtianova, J. Macicek, A. Nenov)

A series of solutions with B2O3 concentrations in the range 89.7-91.7 wt.% was investigated in order to determine the concentration region for growth of inclusions-free LiB3O5 crystals. In the synthesized crystals the formed inclusions were

observed and characterized by optical microscopy, X-ray powder diffraction and electron microscopy. The obtained preliminary results make it possible to choose the proper B2O3 solution compositions for growing inclusions-free LiB3O5 single crystals.

In the macroinclusions (gretaer than 100-200 mm) both LiB3O5, Li2B4O7, Li2B8O13, B2O3 crystalline and amorphous phases were observed. To explain the presence of Li2B4O7 and Li2B8O13 one can suggest LiB3O5 decomposition when cooling the crystal from crystallization to room temperature. The unit cell parameters and the possible space group P 21/m of Li2B8O13 were determined for the first time. The phase decomposition of LiB3O5 to Li2B4O7 and Li2B8O13 was observed during mechanical grinding of the crystals at room temperature. The formation of 2Li2O. 5B2O3 nuclei can be considered as the reason for increasing the amount of microinclusions (less than 100µm) in the grown B2O3 crystals.

22. Structural investigation of Pb5MoO8 single crystals by SAED and HRTEM (D. Nihtianova, V. Yamakov, V. Ivanov)

Six ([100], [010], [001], [011], [101], [110]) SAED and two ([001], [021]) high resolution electron microscopy (HRTEM) images of Pb5MoO8 particles were obtained and analyzed. Due to the modulation of the structure the SAED patterns consist of an intense base set of an a-PbO subcell reflections and of weak superstructure reflections h`/4, k`/3, l`/2 corresponding to the a-PbO unit cell. On the basis of the intensities of SAED patterns and using the model of Pb5SO8 proposed by Sahl a structural model for the positions of the heavy Pb and Mo atoms in Pb5MoO8 single crystals was proposed. This model is tested by comparing the theoretical intensities, calculated by multislice dynamic algorithm with the observed ones in all six measured SAED patterns. The results obtained so far are of a preliminary character.

23. New aspects of the phase diagram PbO-MoO3 (D. Nihtianova, S. Angelova, Ya. Dimitriev, L. Petrov)

The aim of the work is to specify the stability field of Pb5MoO8 in the PbO-MoO3 phase diagram.

Two technological regimes for the synthesis of Pb5MoO8 were used [18]. DTA curve obtained at heating reveals one endothermal peak at 763 °C corresponding to the melting point of Pb5MoO8. At cooling DTA curves contain three exothermal effects at 866 °C, 762 °C and 730 °C. The first one is probably due to traces of Pb2MoO5, the second one to Pb5MoO8 and the third one to PbO.Pb5MoO8 eutectic mixture. The heating of the sample of Pb5MoO8 at 772 °C for 48 h and the subsequent cooling to room temperature lead to its decomposition into PbO (massicot) and Pb2MoO5. DTA and PDA data are in good agreement and indicate that Pb5MoO8 is an incongruently melting compound.

The studies performed by PDA, DTA, SEM, and TEM allow to actualize the processes in the system PbO-MoO3.

24. Growth and characterization of molecular sieve films on various substrates. (V. Valtchev, S. Mintova)

Molecular sieve zeolites are main components in chemical and petrochemical industries, in petroleum refining, and in various adsorption, catalytic and ion-exchange applications. Thin film devices are attractive because they are easily characterised, contain a small amount of material and can often be selectively deposited. Metal supports are especialy convinient for molecular sieve-containing composite materials due to their high thermal stability, acid resistance, and the possibility of forming modules in an arbitrary shape [30,32]. Investigated are the controlling factors and kinetics of the growth process of molecular sieves on metal substrate [30, 32] and vegetal [71] and mullite [33] fibers. The investigations include synthesis of molecular sieves (zeolites A, X, Y, ZSM-5, SAPO-5, etc.) on the aforesaid substrates as well as investigations of the influence of the substrate pretreatement on the process of film deposition, namely on the crystallization kinetics, the physicochemical parameters and morphology of the deposited films.

25. Mechanochemical activation of mineral stuff (A. Toneva, N. Petrova)

The use of poor mineral stuff necessitates the development of new methods for extraction of the useful components through removing the undesirable remainder. The present work deals with the mechanochemical activation of various row materials containing aluminium, iron, cupper, lead-zinc, barium, magnesium, phosphorus, vermiculite and zeolites. The tribochemical activations were carried out in a vortex apparatus with rotative magnetic field and in an agate planetary ball mill. Then, the heats of immersion of mechanochemically activated clinoptilolite in methylenblue solutions as well as the heats of ion-exchange of the obtained forms were determinated by calorimetric measurements. These parameters are greater for the mechanochemically activated forms than for the nonactivated ones due to dispersion of the solid phase, to changes in the grain size and to lattice defects.[31].

The influence of the mechanical activation of natural phosphate used for production of phosphoric acid, phosphates and salts was investigated in detail by different triboreactors. It is proved that the mechanical activation leads to an increase in the content of assimilatable P2O2 to values comparable with those obteined by the power consuming and ecollogically dangerous conventional acid technology. In addition, the mechanochemical method, combined with thermal treatment, allows also an easier removal of the undesirable impurities due to the combined thermal tribochemical effect, thus producing higher contents of P2O5.

26. Utilization of natural and modified zeolites and montmorillonites as filters and sorbents (L. Filizova, B. Vassileva)

The sorption properties and capacity of natural clinoptilolite tuff from Beli plast deposit, Bulgaria, and montmorillonite clays from Dimitrovgrad region, Bulgaria, as well as their Na-exchanged forms were studied. The clinoptilolite sample was modified by ion-exchange either in NaNO3 or in Na2CO3 solution. The former modification was combined with active carbon to create a filter material with properties suitable for additional purification of drinking water (accepted for serial production, #47-220-1157/1995), while the latter one showed properties suitable for softening of water for daily needs.(Bulg. patent reg. #99381/1995). Based on the specific cation-exchaged properties in contact with solutions clinoptilolite-montmorilonite compositions are now being studied as combined filters. Another variant is designed for purification of solutions from anions based on the ability of bentonite to sorb anions and anion groups.

IV. STRUCTURE AND PROPERTIES OF MINERALS AND NEW MATERIALS. PHYSICAL AND CHEMICAL CHARACTERIZATION

27. Structural and phase characterization of new crystalline materials
(J. Macicek, O. Angelova, K. Kosev Y. Georgieva, R. Petrova, T. Todorov,
S. Bakardjieva, M. Tarassov, A. Toneva)

Twenty three crystalline phases were investigated including simple and double selenates, selenites and hydroselenites as well as adducts of inorganic salts with organic molecules (urea, thiourea, pyrophosphates and pyrovanadates), some perrhenates with nicotinic and isonictinic hydrazide, etc. The hydrates of rare-earth selenates are used for preparing materials with non-linear electronic properties and ceramic luminophors. The investigation includes synthesis, determination of the crystal structures and corrundum number (RIR), registration and processing of the powder XRD data [56, 57, 64, 65]. Two computer programs were developed, one for calculating RIR of the theoretical powder patterns on the basis of known structure, aiming at the elucidation of preferable orientations in the studied samples, and another for preparation of the experimental results according to the requirement of the International Union of Crystallography.

28. Structural and thermodynamic parameters of inorganic disordered systems (L. Konstantinov, N. Zotov, E Dinolova, A. Toneva, N. Petrova,
B. Mihailova, M. Marinov)

The vibrational spectra, the structure and the thermodynamic parameters of various synthetic and natural objects such as silicate and metasilicate glasses and ceramics, tungstens, quartz, wollastonite and zeolites, are studied systematically. The investigations are based on modelling the spectra in various cluster approximations and on experimental data obtained by X-ray diffraction, Raman and IR spectroscopy, thermal analysis and electron microscopy. The obtained results provide information on the structure, the degree of crystallinity and the influence of different types of disorder on the properties of the materials under study [14, 27, 67, 69, 70]. On the basis of the Green's function method the disorder-induced mode coupling in glasses and its effect on the intensity of the first-order Raman and IR spectra were discussed [68, 82, 83]. A set of structural parameters is introduced to describe the vibrational behaviour of rings of SiO4 tetrahedra and it is shown that the presence of a given type of disorder leads to broadening of the spectral lines and to changes in the integral Raman intensities.

The thermodynamic properties and the processes of ion-exchange and sorption of natural zeolites (heulandite, clinoptilolite, chabazite) are investigated by low- and high-temperature Calve type calorimeters [21, 22, 75, 76]. The zeolitazation of volcanic glasses is studied calorimetrically for the first time and it is shown that all processes involved, namely the glass hydration and dissolution as well as the crystallization of zeolite minerals are exothermic. The addition of seeds influences the mineralogical composition of the synthesized products and the zeolitazation kinetics and enthalpy.

29. Modelling of spectral characteristics of noncollinear acousto-optic tunable filters of TeO2 (G. Georgiev, L. Konstantinov)

On the basis of a simple mathematical model the spectral dependencies of the bandpass width, the spectral resolution and the diffraction efficiency of a noncollinear acousto-optic tunable filter of TeO2 are calculated [6]. The effect of four operation parameters, namely the directions of propagation of the acoustic and optic waves, the length of acousto-optic interaction, and the power density of the controlling RF-signal, on the filter spectral characteristics is discussed and illustrated from the viewpoint of practical applications. An example of the filter design using these dependencies is presented.

30. Static and dynamical properties of ferromagnetic semiconductors and ferroelectrics with hydrogen bonding (J. Weselinova, A. Apostolov,
M. Marinov)

A Green's function technique is used for studying the effects of spin-phonon interactions in squaric acid (C4H2O4) [43]. The Ising model hamiltonian in a transverse field including four-spin interaction, responsible for the first-order phase transition observed in order-disorder ferroelectrics, is analyzed taking into account higher order anharmonic phonon interaction terms. The renormalized energy and the damping of the spin waves on the one hand, and the phonon spectrum on the other hand, are determined for the first time. The anharmonicity effects play an important role around and above the phase transition temperature, Tc. It is shown that below Tc the spin-wave damping increases nonlinearly with increasing the temperature. The major part of this damping comes from spin-spin and spin- phonon interactions, the latter contributing to the damping in the vicinity of Tc = 373 K. The temperature dependence of the frequency and the damping of the phonon mode at about 90 cm-1 are studied in detail. It is shown that while the mode frequency decreases with increasing the temperature and approaches 83 cm-1 at T = Tc, the damping increases with increasing the temperature. The temperature behaviour of this phonon mode is in a very good agreement with the experimental data.

31. Geometrization of the fundamentals of Chemistry (V. Penev,
L. Konstantinov, M. Marinov)

The aim of this project is to start a qualitatively new, higher evolutionary stage in the development of the language of chemistry, the stage of its geometrization. For this purpose:

  • A system of starting hypotheses, concerning the different evolutionary stages in the development of scientific branches and sciences is formulated.
  • Using these hypotheses the particular problem for geometrization of the language of chemistry is formulated in a general form and grounded in a detail.
  • The way for solving this problem is outlined by formulating a system of four basic problems to be solved during the next evolutionary stage of the development of the language of chemistry.
  • Logical analysis of the foundations of chemistry is performed and their logical structure is specified. A number a categories and basic chemical notions are correctly defined.
  • The conceptual, logical and mathematical formalism, necessary for an entirely mathematical reformulation of the language of chemistry are developed.
  • Methods are proposed for construction of entirely mathematical spatial representations of the basic chemical notions and relationships.
  • Using the developed formalism and methods, entirely mathematical spatial representations of a number of basic chemical notions and relations are constructed.
  • A number of basic chemical statements, which form a substantial part of the future mathematical and, at the same time, axiomatic formulations of the chemistry, are formulated mathematically and proved.

A monograph on this subject is now in preparation.

INTERINSTITUTES PROGRAMS:

  • Synthesis and structural characterization of palladium catalysts supported on volcanic glasses from the island of Lipari (Italy) and from the Eastern Rhodopes mountains (Bulgaria). A collaboration with ICTPN-CNR (Instituto di Chimica e Technologia dei Prodotti Naturali del CNR via Archirafi), Palermo, Italy;
  • Spectroscopic and thermochemical studies of silicate glasses, Cd-Si-oxide pollyphase ceramics and new materials. A collaboration with Institute of Ceramic and Glass, Madrid, Spain;
  • X-ray diffraction of miscellaneous phases. A collaboration with International Centre for Diffraction Data (ICDD-JCPDS), USA.

POSTDOCTORAL FELLOWS:

  • Dr. Nikolay Zotov - Cadiz University, Spain;
  • Dr. Valentin Valtchev - Lulea University, Sweden;

PUBLICATIONS AND REPORTS AT CONFERENCES AND LOCAL MEETINGS:

PUBLISHED ARTICLES AND REPORTS:

1. Damyanov, Z. 1995. Zoning of the Kremikovtsi marble onyx. - Compt. rend. Acad. bulg. Sci., 48, 3, 33-36.

2. Damyanov, Z. 1995. Decorative calcite from the Kremikovtsi deposit. - Rev. Bulg. Geol. Soc., 56, 2, 19-34 (in Bulgarian, with English abstract).

3. Damyanov, Z. 1995. Mineralogy, zoning and genesis of the deposit. - In: The Kremikovtsi iron-barite ore deposit and the Jurassic system in the region. A guide-book. Univ. Mining and Geology, Sofia, 15-23 (in Bulgarian).

4. Damyanov, Z. 1995. Exploration criteria for stratiform iron-barite-polymetallic carbonate-hosted deposits in the Sredec ore region. - In: Metallogeny of Bulgaria, Proceed. Second Nation. Symp., Sofia, 35-38 (in Bulgarian).

5. Damyanov, Z. 1995. Triassic metallogenesis in the West Balkan. - Compt. rend. Acad. bulg. Sci., 48,11-12, 75-78.

6. Georgiev, G., L. Konstantinov. (1995). Design of the bandpass width, the spectral resolution and the diffraction efficiency of a non-collinear acousto-optic tunable filter. - Optics & Laser Technol. 27,383-387

7. Khrischev, K., I. Vaptzarov, I. Godev, T. Dachev, N. Zidarov, V. Kotzev, L. Tzenov and V. Sharov. 1995. Earth Sciences and the 21st century challenges. - Journ. Bulg. Acad. Sci., 1, 4-10 (in Bulgarian, with English abstract).

8. Kirov, G., S. Hristov and M. Tarassov. 1995. An unusual phenomenon observed during the heating of man-made quartz crystals. - Compt. rend. Acad. bulg. Sci., 48, 2, 73-75.

9. Kostov, I, N. Zidarov and V. Breskovska. 1995. Current state and problems of mineralogy during the period of transition to market economy. - Mining and Geology, 4, 27-29 (in Bulgarian, with English abstract).

10. Kostov, V. 1995. Syntheses and crystal-chemical characteristics of chlorsulfosalts. - Ann. Univ. Sofia, Livre 1-Geol., 87, 47-58 (in Bulgarian, with English abstract).

11. Kostov, V. 1995. Syntheses and crystal-chemical features of Pb-Sb chlorsulfosalts. - Summary of PhD thesis, 30 p. (in Bulgarian).

12. Kostov, V. and J. Macicek. 1995. Crystal structure of synthetic Pb13Sb11S28Cl 3 - a new view of the crystal chemistry of chloring-bearing lead-antimony sulphosalts. - Eur. J. Mineral., 7, 1007-1018.

13. Kostova, I., O. Petrov and J. Kortenski. 1995. Mineralogy, geochemistry and pyrite content of Bulgarian subbituminous coals, Pernik basin. - Coalbed Methane and Coal Geology, R. Gayer and I. Harris, eds., London, 97, 301-314.

14. Mihailova, B., L. Konstantinov and E. Dinolova. 1995. Cluster-approximation modelling of infrared and Raman spectra of crystalline and vitreous CaSiO3. - J. Non-Cryst. Solids, 191, 79-84.

15. Minchev, C., Valtchev, V. and S. Mintova. 1995. Thermal analysis of the crystallization of SAPO-5. - Thermochimica Acta, 2410, 1-8.

16. Mintova, S., V. Valchev and I. Kanev. 1995. Structure-controlled effect of organic templates on zeolite crystallization. - Molecular Eng., 4, 369.

17. Mouhovski, J. and O. Vitov. 1995. Calcium fluoride crystals growth using material from Zidintsi deposit - Geology and Mineral Resources, 8, 23-28 (in Bulgarian, with English abstract).

18. Nihtianova, D., S. Angelova, L. Djonev, T. Zheleva and E. Tsukeva. 1995. Phase inhomogeneity of Pb2MoO5 single crystals. - J. Crystal Growth, 148, 148-154.

19. Petrov, O. 1995. Cation exchange in clinoptilolite: an X-ray powder diffraction analysis. - Natural Zeolites'93, D. Ming and F. Mumpton, eds., 271-279.

20. Petrova, N., L. Filizova and G. Kirov. 1995. Calorimetric study of Na-K ion-exchange in clinoptilolite. - Natural Zeolites'93: Occurrence, Properties, Use, Eds. D. Ming, F. Mumpton, Brockport, N.Y., 281-287.

21. Petrova, N. and D. Kirov. 1995. Heats of immersion of clinoptilolite and its ion-exchanged forms: a calorimetric study. - J. Thermal Analysis, 43, 323-328.

22. Petrova, N., G. Kirov. 1995. Zeolitization of glasses: a calorimetric study. - Thermochimica Acta, 269/270, 443-452.

23. Piperov, N. and B. Zidarova. 1995. Fluid inclusions in synthetic fluorite crystals - checking of analytical procedures and thermal investigations. A priori stretched inclusions? - N. Jb. Miner. Mh., 5, 224-240.

24. Ratiev, L. and Z. Damyanov. 1995. Geochemical features of the Kremikovtsi siderite ore. - Mining and Geology, 50, 5, 5-9 (in Bulgarian, with English abstract).

25. Tarassov, M. 1995. The phase WO3.1/3H2O as a primary product of the scheelite decomposition in sulphuric acid dilute solutions: experimental data and natural analogues - Geochem. Mineral. and Petrol, 30, 19-30 (in Russian, with English abstract).

26. Tchoumatchenco, P., T. Nikolov, D. Kozhoukharov, B. Benev, P. Gocev, N. Katzkov, K. Khrischev, M. Moev, Z. Nikolov, I. Slavov, D. Stoitchev, T. Tzankov and N. Zidarov. 1995. Le Cretace inferieur dans le Massif de l'Ouarsenis et les Monts de Tiaret (Algerie du Nord). - Geol. Balc., 25, 2, 27-59.

27. Toneva, A., M. Marinov, B. Mihailova and L. Konstantinov. 1995. The effect of disorder on the thermodynamic parameters of silicate glasses. - Thermochimica Acta, 269-270, 453-456.

28. Tzvetanova, Y. 1995. Corkite from Brussevtzi deposit, Eastern Rhodope massif, Bulgaria. - Compt. rend. Acad. bulg. Sci., 48, 5, 47-50.

29. Tzvetanova, Y. and L. Grozdanov. 1995. Pyroxenes from Eocene sediments from the quarry in the area of village Novoseltzi, Burgas district - Geochem. Mineral. and Petrol, 30, 51-62 (in Bulgarian, with English abstract).

30. Valtchev, V. and S. Mintova. 1995. The effect of the metal substrate composition on the crystallization of zeolite coatings. - Zeolites, 15, 171-175.

31. Valtchev, V., S. Mintova, V. Dimov, A. Toneva and D. Radev. 1995. Tribochemical activation of seeds for rapid crystallization of zeolite Y. - Zeolites, 15, 193-197.

32. Valtchev, V., S. Mintova, L. Konstantinov. 1995. Influence of the metal substrate properties on kinetics of zeolite film formation. - Zeolites, 15, 679-683.

33. Valtchev, V., S. Mintova, B. Schoeman, L. Spasovand L. Konstantinov. 1995. Zeolite crystallization on mullite fibers - Zeolites:A Refined Tool for Designing Catalitic Sites, L. Bonneviot & S. Kaliaguine, Eds., Elsevier Sci, B.V., 527-532.

34. Vassilev, S. 1995. Phase-mineralogical studies on solid waste products from burning of Bobov Dol coal at "Bobov Dol" thermo-electric power plant. - Ann. Univ. Sofia, Livre 1-Geol., 84, 85-108. (in Bulgarian)

35. Vassilev, S. 1995. Stack emissions from coal-fired power stations: an environmental pollution with trace elements. - Compt. rend. Acad. bulg. Sci., 48, 4, 45-47 (in Bulgarian).

36. Vassilev, S., G. Eskenazy, M. Tarassov and V. Dimov. 1995. Mineralogy and geochemistry of a vitrain lens with unique trace element content from the Vulche Pole coal deposit, Bulgaria. - Geol. Balc., 25, 3/4, 111-123.

37. Vassilev, S., K. Kitano, S. Takeda and T. Tsurue. 1995. Influence of mineral and chemical composition of coal ashes on their fusibility. - Fuel Process. Technol., 45, 27-51.

38. Vassilev, S., K. Kitano, S. Takeda and T. Tsurue. 1995. Relationship between fusibility and mineral and chemical composition of coal ashes. - Compt. rend. Acad. bulg. Sci., 48, 7, 51-54.

39. Vassilev, S., M. Yossifova and S. Valceva. 1995. Petrographical, mineralogical and chemical composition of coals and waste products from Bobov Dol Central Coal-tretment Plant. II. Mineralogical and chemical composition. - Ann. Univ. Sofia, Livre 1-Geol., 87, 103-123 (in Bulgarian, with English abstract).

40. Vassileva, C. 1995. Structure and microrelief of quartz pebbles from the Novoseltzi sedimentary deposit. - Rev. Bulg. Geol. Soc., vol. 56, 1, 93-102 (in Bulgarian, with English abstract).

41. Vitov, O. 1995. Schlich-mineralogical zoning, exploration prognoses and evaluation of knowledge of the Eastern Rhodope massif. - In: Metallogeny of Bulgaria, Proceed. Second Nation. Symp., Sofia, 19-23 (in Bulgarian).

42. Vitov, O. 1995. Schlich-mineralogical map of Bulgaria. - Geology and Mineral Resources, 4, 6-11 (in Bulgarian, with English abstract).

43. Wesselinowa, J., A. Apostolov and M. Marinov. 1995. The Green's function technique for spin-phonon interactions in squaric acid. - J. Phys.: Condens. Matter, 7, 1701-1709.

44. Yossifova, M., S. Valceva and S. Vassilev. 1995. Petrographical, mineralogical and chemical composition of coals and waste products from Bobov Dol Central Coal-tretment Plant. I. Petrographical composition. - Ann. Univ. Sofia, Livre 1-Geol., 87, 85-101 (in Bulgarian, with English abstract).

45. Zidarov, N. and P. Nenova. 1995. Basic and ultrabasic rocks and related eclogites from the Serbo-Macedonian massif (SW Bulgaria). - Proc of the XV-th Congress of KGBA, Athens, Greece, N 4/2, 619-626.

46. Zidarov, N., P. Nenova and V. Dimov. Coesite in kyanite eclogite of Ograzden Mts, SW Bulgaria. - Compt. rend. Acad. bulg. Sci, 48, 11-12(1995)59-62.

47. Zidarova, B. 1995. Type and distribution of the fluorite chemical inhomogeneity in Slavyanka deposit. - Geochem. Mineral. and Petrol, 30, 99-106 (in Bulgarian, with English abstract).

48. Zidarova, B. 1995. The distribution of La and Tb in hydrothermal fluorite from the Slavyanka deposit as an indication for the processes of rearrangement and redeposition. - Compt. rend. Acad. bulg. Sci., 48, 3, 37-40.

49. Zidarova, B. and N. Piperov. 1995. Temperature and molecular composition of the mineral-forming fluids in Slavyanka deposit. - Rev. bulg. Geol. Soc., vol. 56, 2, 9-18 (in Bulgarian, with English abstract).

50. Zidarova, B. and N. Zidarov. 1995. Mechanism of fluorite formation in hydrothermal paleokarst of the Mikhalkovo deposit. - Compt. rend. Acad. bulg. Sci., 48, 3, 41-43.

51. Zidarova, B. and N. Zidarov. 1995. Basic elements of the geogenetic model of Fluorite formation: I. The Slavyanka deposit. - Compt. rend. Acad. bulg. Sci., 48, 8, 33-36.

52. Zidarova, B. and N. Zidarov. Basic elements of the geogenetic model of Fluorite formation: II. The Mikhalkovo deposit. - Compt. rend. Acad. bulg. Sci., 48, 9-10, 87-90.

53. Zidarova, B. and N. Zidarov. 1995. Processes of fluorite formation in the Slavyanka deposit, SW Bulgaria. - Proc. Of the XV-th Congress of KGBA, Athens, Greece, N 4/2, 869-872.

54. Zotov, N., H. Boysen, C. Romano, D. Dingwell and Y. Yanev. 1995. Neutron diffraction study of feldspar glasses. Mixed alkali effect. - J. Non-Cryst. Solids., 191, 124-131.

55. N. Zotov, F. Frey, H. Boysen, H. Lehnert, A. Hornsteiner, B. Strauss, R. Sonntag, M. Mayer, F. Guthof, D. Hohlwein. 1995. X-ray and neutron diffuse scattering in LiNbO3 from 38 to 1200K. - Acta Crystallogr. B51, 961-972.

PUBLICATIONS IN PRESS:

56. Angelova, O. Thiourea adducts of M(ReO4)2.M = Pb, Cd. - XVI Europ. Crystallogr. Meeting, ECM-16, Lund, Sweden.

57. Angelova, O., J. Macicek, R. Petrova, T. Todorov and B. Mihailova. Structure of molecular adducts of inorganic salts IV. - Z. Kristallogr.

58. Damyanov, Z. Primary ore petrology, whole-rock chemistry and zoning of the Kremikovtsi carbonate-hosted submarine exhalative iron(+Mn)-barite-base metal deposit, West Balkan, Bulgaria. - N. Jb. Miner. Abh.

59. Georgieva, I., I. Ivanov and O. Petrov. X-ray powder diffraction data for Ba3MnSi2O8 - a new phase in the system BaO-MnO-SiO2. - Powder Diffraction.

60. Kossev, K. and N. Kosseva. - Spectroscopic determination of cyclic carbonates and cyclic carbonate content in polymers. - III Intern. Conf. of the Applied Spectroscopy, 25-30.10.1995, Blagoevgrad (in Bulgarian).

61. Kostova, I., K. Markova and K. Kantchev. Mossbauer spectroscopic investigation of low rank coal lythotypes. - Proc. of the European Coal Conf., Praha.

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

63. Lazarova, V., S. Mintova and V. Valchev. Influence of zeolite flocculation in paper on its optical characteristics. - Bulg. Chem. Commun.

64. Macicek, J. Urea-water completion and competition in divalent perrhenates. - XVI Europ. Crystallogr. Meeting, ECM-16, Lund, Sweden.

65. Macicek, J. and O. Angelova. Molecular adduct of inorganic salts III - Acta Crystal., C 51.

66. Maleev, M. Chr. Hydrothermal growth of man-made corundum crystals. - Rev. bulg. Geol. Soc.

67. Marinov, M., M. Tarassov, N. Zotov and L. Konstantinov. Raman study of WO3.nH2O (n = 1/2, 1/3). - Balkan Phys. Lett.

68. Marinov, M., N. Zotov and L. Konstantinov. Disorder-induced intermode interactions and their effect on Raman spectra of glasses. - Proc. of the 8th Intern. Conf. on Physics of Non-crystalline Solids, Turku, Finland.

69. Mihailova, B., N. Zotov and L. Konstantinov. Infrared absorption spectra of deformed rings of SiO4 tetrahedra. - Balkan Phys. Lett.

70. Mihailova, B., V. Valtchev, S. Mintova and L. Konstantinov. Vibrational spectra of ETS-4 and ETS-10. - Zeolites, 16.

71. Mintova, S. and V. Valchev. - Deposition of zeolite A on vegetal fibers. - Zeolites.

72. Mintova, S., V. Valtchev and S. Angelova. The role of Na and K ions in the crystallization of titanium silicate ETS-4. - Proc. of the 12th Intern. Zeolite Conf., Seoul, Corea.

73. Mouchovski, J., I. Haltakov and V. Lyutskanov. Growth of ultra violet grade CaF2 crystals and their application to excimer laser optics. - J. Crystal Growth.

74. Opalchenova, G., E. Dyulgerova and O. Petrov. A study of the influence of biphase calcium phosphate ceramics on bacterial strains - in vitro approach. - J. Biomedical Mater. Research.

75. Petrova, N., L. Filizova and G. Kirov. Calorimetric study of ion-exchange of monocation forms of clinoptilolite from Beli Plast deposit. - Proc. of the Sofia Zeolite Meeting'95.

76. Petrova, N., L. Filizova, G. Kirov. Comparative calorimetric investigation of the ion-exchange of clinoptilolite and mordenite. - Proc. of the Sofia Zeolite Meeting'95.

77. Todorov, T., O. Angelova and J. Macicek. The covered water in the structure of Sr(ReO4)2.2H2O: a revision of the sesquihydrate model. - Acta Crystal., C 52.

78. Tsintsov, Z. and L. Grozdanov. Silicate inclusions in platinum-group minerals isolated from sediments of the Blagoevgrad graben, SW Bulgaria. - Compt. rend. Acad. bulg. Sci., 49, 2.

79. Valtchev, V., S. Mintova, B. Mihailova and L. Konstantinov.Comparison of physicochemical properties of Zorite and ETS-4. - J. Mater. Res. Bull.

80. Valtchev, V., S. Mintova, B. Mihailova and L. Konstantinov. Comparative investigation of zorite and its synthetic counterpart ETS-4. - Proc. of the Sofia Zeolite Meeting'95.

81. Vassileva, B., S. Vassilev and C. Vassileva. Effective use of mineral sorbents for purification of waste waters from thermo-electric power stations. - Compt. rend. Acad. bulg. Sci., 49, 4.

82. Zotov, N. and M. Marinov. Vibrational dynamics of glasses - Raman spectra calculations, dynamical properties of solids. - Dynamical Properties of Solids, DYPROSO XXV, HARO, La Rioja, Spain.

83. Zotov, N., M. Marinov and L. Konstantinov. Degree of structural disorder in sodium metasilicate glass - Raman spectroscopy study. - J. Non-Cryst. Solids.

Reports and posters at scientific events:

84. Angelova, O. - Report at the XVI Europ. Crystallogr. Meeting, ECM-16, 6-11. 08. 1995, Lund, Sweden;

85. Damyanov, Z. - Report at the National Conf. Metallogeny of Bulgaria, 23-24.11.1995, Sofia, Bulgaria;

86. Macicek, J. - Report at the Meeting on Rietveld method, 18-23. 07. 1995, Moscow, Russia;

87. Macicek, J. - Report at the XVI Europ. Crystallogr. Meeting, ECM-16, 6-11. 08. 1995, Lund, Sweden;

88. Mintova, S. - Report at the Int. Symp. on Catalysis by Microporous Materials, 9-13.07.1995, Sombathey, Hungary;

89. Mintova, S. and V. Valtchev - Report at the II National Conf. of Chemistry, 12-14.04.1995, Plovdiv, Bulgaria

90. Petrov, O. - Report at the Sofia Zeolite'95 Meeting, 18-25.06.1995, Sofia, Bulgaria;

91. Petrova, N. - 2 Reports at the Sofia Zeolite Meeting'95, 18-25.06.1995, Sofia, Bulgaria;

92. Tsintsov, Z. - Reports at the National Conf. on Mineral-resource base in Kjustendil area. State and perspectives, 26-27.05.1995, Kjustendil, Bulgaria;

93. Valtchev, V. - Report at the Int. Symp. on Catalysis by Microporous Materials, 9-13.07.1995, Sombathey, Hungary;

94. Valtchev, V. and S. Mintova - Report at the II National Conf. of Chemistry, 12-14.04.1995, Plovdiv, Bulgaria;

95. Valtchev, V., S. Mintova, B. Mihailova and L. Konstantinov - Report at the Sofia Zeolite'95 Meeting, 18-25.06.1995, Sofia, Bulgaria;

96. Vitov, O. - 3 reports at the National Conf. on Mineral-resource base in Kjustendil area. State and perspectives, 26-27.05.1995, Kjustendil, Bulgaria;

97. Vitov, O. - Report at the National Conf. Metallogeny of Bulgaria, 23-24.11.1995, Sofia, Bulgaria;

98. Zidarov, N. - Report at the MAEGS-9 Conference on Precambrian in Europe, 2-9.09.1995, St. Petersburg, Russia;

99. Zidarov, N., P. Nenova - Report at the XV Congress KGBA, 17-20.09.1995, Athens, Greece;

100. Zidarova, B., N. Zidarov - Report at the XV Congress KGBA, 17-20. 09. 1995, Athens, Greece;

101. Zotov, N. - Seminar at the Bayerisches Geoinstitute, University of Bayreuth, 3.08.1995, Bayreuth, Germany;

102. Zotov, N. - Seminar at the Institute of chemistry and technology of natural products, Univresity of Palermo, 13.11.1995, Palermo, Italy

103. Zotov, N. - Seminar at the Department of Solid State Physics, University of Cadiz, 8.12.1995, Cadiz, Spain