Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOsciences <![CDATA[ Foreword to the special issue “From experimental mineralogy and crystallography to mineral deposit: a tribute to Milan Drábek” ]]> Laufek F, Kotková J; Vol. 66, issue 4, page: 185
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<![CDATA[ Milan Drábek: Bright, productive, witty, provocative ]]> Kotková J; Vol. 66, issue 4, pages 187 - 188
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<![CDATA[ Perryite, (Ni,Fe)16PSi5, from the Mount Egerton aubrite: the first natural P-Si-ordered phosphide-silicide ]]> Britvin SN, Krivovichev SV, Vereshchagin OS, Vlasenko NS, Shilovskikh VV, Krzhizhanovskaya MG, Lozhkin MS, Obolonskaya EV, Kopylova YO; Vol. 66, issue 4, pages 189 - 198
Perryite, natural Ni-silicide, is a minor but regular constituent of the metal phase in enstatite chondrite (aubrite) and enstatite chondrite meteorites. Its synthetic analog was shown to have promising catalytic properties. The first-time solution of the crystal structure of natural perryite was completed on the material from the Mount Egerton aubrite. The mineral is trigonal, R͞3c, a = 6.6525(5), c = 37.998(5) Å, V = 1456.3(3) and Z = 6. The structure was refined to R1 = 0.0137 based on 457 independent observed reflections. The chemical formula obtained from the structure refinement, (Ni14.14Fe1.88)Σ16.02PSi5, agrees with that derived from the electron microprobe data, (Ni13.39Fe2.65Co0.01)Σ16.05P1.22Si4.74. This research showed that P and Si in perryite are ordered, resulting in the simplified formula (Ni,Fe)16PSi8, in contrast to the currently accepted variant (Ni,Fe)8(Si,P)3. The detailed results of EBSD study reveal previously unknown relationships between perryite, associated α-(Fe,Ni) metal (also known as kamacite) and schreibersite, (Fe,Ni)3P. Since enstatitic meteorites represent the early stages of nebular accretion, our results demonstrate that the crystal-chemical factor could affect the differentiation of chemical elements upon the onset of the Solar System formation. ]]> Original paper
<![CDATA[ The Hg-Pd-Te system: phase relations involving temagamite and a new ternary phase ]]> Drábek M, Vymazalová A, Laufek F, Tuhý M; Vol. 66, issue 4, pages 197 - 204
Phase relations in the Hg-Pd-Te system were studied at 350 °C using the silica glass tube method. The following binary phases were confirmed to be stable at 350 °C: PdHg (potarite), HgTe (coloradoite), Pd13Te3, Pd20Te7 (keithconnite), Pd7Te3, Pd9Te4 (telluropalladinite), Pd3Te2, PdTe (kotulskite), and PdTe2 (merenskyite). Kotulskite (PdTe) dissolves up to 8 at. % Hg at 350 °C. Other palladium tellurides do not dissolve Hg. Two ternary phases were proved to be stable in the system at 350 °C: Pd3HgTe3 (temagamite) and a new phase Pd4HgTe3. The Pd4HgTe3 phase is orthorhombic, Pnma space group with unit-cell parameters a = 13.1520(2), b = 11.6879(2), c = 4.25758(5) Å, V = 654.480(5) Å3 and Z = 4. The Pd4HgTe3 phase can be viewed as a ternary ordered variant of the Hg-bearing kotulskite. Synthetic temagamite forms stable assemblages with several phases representing minerals merenskyite and coloradoite, coloradoite and potarite, merenskyite and kotulskite, phase Pd4HgTe3 and kotulskite s.s., and phase Pd4HgTe3 and potarite. The occurrence of temagamite and its associations indicate the formation of mineralization below 570 °C. The new phase Pd4HgTe3 forms stable associations with synthetic analogs of temagamite and potarite, potarite and telluropalladinite, telluropalladinite and kotulskite s.s., temagamite and kotulskite s.s. The phase Pd4HgTe3 can be expected to be found in such associations under natural conditions. ]]> Original paper
<![CDATA[ Ag, Cu, Hg, Pt, Sb and Te substitutions in the synthetic analogue of palladseite, Pd17Se15: an experimental mineralogical study ]]> Laufek F, Vymazalová A, Tuhý M; Vol. 66, issue 4, pages 205 - 213
The solubility of Ag, Cu, Hg, Pt, Sb and Te in the synthetic analogue of palladseite was experimentally studied at 350 °C. To document the impact of these elements on the palladseite crystal structure, Rietveld refinement analysis of experimental products was performed. The synthetic Pd17Se15 dissolves at 400 °C 3.6, 6.4, 8.8, 9.7, 6.1 wt. % of Cu, Ag, Hg, Pt and Te, respectively. The solubility of Sb in synthetic Pd17Se15 is less than 0.03 wt. %. Three different types of incorporation of the above-mentioned elements to the palladseite structure have been observed. Ag, Cu and Hg occupy a position 3d of the Pm-3m space group, which was empty in the unsubstituted Pd17Se15. Consequently, Pd occupancy of adjacent [Pd(4)Se6] octahedron is reduced to 0.46 and 0.51 for Cu and Ag-bearing palladseite, respectively. Incorporation of Hg to the palladseite structure causes vacancy of this Pd(4) position. Pt partially substitutes Pd at the Pd(2) position (6f ), forming Pd0.41/Pt0.59 mix site showing square-planar coordination by Se atoms. Te atoms substitute for Se. The refined unit-cell parameter increased from the initial value of a = 10.6074(1) Å for Pd17Se15 to 10.6680(1) Å for Te-bearing palladseite. Incorporation of Cu, Ag and Hg to the palladseite causes significant changes of its powder X-ray diffraction pattern and hence can be detected by PXRD. ]]> Original paper
<![CDATA[ Miscibility between synthetic FeS and TiS: An insight into the phase relations in natural Ti-bearing iron monosulfides ]]> Mészárosová N, Skála R, Mikysek P, Drábek M; Vol. 66, issue 4, pages 215 - 225
Syntheses of (Fe,Ti)S analogs of natural Ti-bearing troilites were performed in evacuated and sealed silica glass tubes to investigate the extent of the knowledge on the solid solution between FeS and TiS. The synthesized (Fe,Ti)S phases were investigated using electron probe microanalysis and powder X-ray diffraction. The synthetic phases of the (Fe,Ti)S series adopt NiAs-type structure of P63/mmc space group in the compositional range from FeS to Fe0.5Ti0.5S. Members of the series rich in titanium crystallize in the R-3m space group. The stoichiometric TiS can adopt both structure types. Some additional diffraction peaks were observed in numerous samples. However, due to the insufficient quality of powder XRD data, crystal structure parameters of only samples with troilite 2C superstructure could be successfully refined. Systematic variation of deficit in metal (Me = Fe + Ti) site occupancy with titanium content was observed in the synthetic samples. This deficit increases with the increasing Ti content in a compositional range from pure FeS to Fe0.2Ti0.8S. In samples containing more titanium than this composition, the deficit of the metal site occupancy decreases, and the composition of end-member TiS is very close to the ideal stoichiometry. ]]> Original paper
<![CDATA[ Cronstedtite from Litošice, Czech Republic ]]> Hybler J, Dolníček Z, Sejkora J; Vol. 66, issue 4, pages 227 - 242
The layered iron silicate cronstedtite was encountered in ore veins in the exploration shaft mined in the Neoproterozoic black shale-hosted pyrite-manganese deposit near Litošice (Eastern Bohemia, Czech Republic) around 1955. It forms up to 2 mm thick black double or single bands in symmetrically zoned hydrothermal veins cutting shales. The specimens selected from available material were studied by single-crystal X-ray diffraction using the four-circle diffractometer with an area detector. The chemical composition of some of the specimens was determined by the electron probe microanalysis (EPMA) in the WDS mode. Furthermore, a polished section of the ore material with cronstedtite bands was prepared, and the mineral association was analyzed with the aid of back-scattered electron (BSE) images. The interpretation of reciprocal space (RS) sections produced by the diffractometer software allowed the determination of OD subfamilies (Bailey’s groups) A, B, C, D, and polytypes. The 1T polytype (subfamily C), a = 5.52, c = 7.12 Å, space group P31m, is the most abundant in the occurrence. In rare cases, it forms oriented crystal associations (allotwins) with the 1M polytype (subfamily A), a = 5.52 Å, b = 9.55, c = 7.136 Å, β = 104.4°, space group Cm. Fully disordered allotwinned crystals of the A+C subfamilies were found, too. In addition, few allotwins of the polytype 2H1 (subfamily D) with a small amount of 2H2, were identified. Unit cell parameters are a = 5.49, c = 14.21 Å, space groups are P63cm (2H1), and P63 (2H2). EPMA-WDS of selected crystals of prevailing 1T polytype revealed elevated contents of Mn (0.19-0.62 apfu) and low contents of Mg (up to 0.13 apfu) and Cl (up to 0.05 apfu), respectively. More rare 2H1 (+2H2) polytypes show elevated contents of Mg in the range of 0.19-0.62 apfu and distinctly lower Mn (up to 0.07 apfu) and Cl contents (up to 0.01 apfu). The BSE images reveal that cronstedtite bands are associated with multiple generations of carbonates (rhodochrosite, siderite, rarely magnesite and calcite), quartz, opal, pyrite and carbonate-fluorapatite. Intense metasomatic replacement of cronstedtite by opal and siderite appeared especially around the center of the studied vein. ]]> Original paper
<![CDATA[ Amphibole and pyroxene as indicators of alkaline conditions in banded carbonatite-like marbles from Bližná, Český Krumlov Unit, Moldanubian Zone ]]> Radková P, Novák M, Cempírek J, Houzar S, Škoda R; Vol. 66, issue 4, pages 243 - 262
Amphiboles and diopside occur in several distinct mineral assemblages in banded carbonatite-like marbles from the Bližná graphite mine, Český Krumlov Unit, Moldanubian Zone. The carbonatite-like marble is interlayered with dominant ordinary metacarbonates as a single continuous stratabound layer, up to 3-4 m thick. It is enriched in elements typical for carbonatites (REE, Y, Th, Sr, Nb, Zr, and Mo) and contains accessory betafite-pyrochlore and uranothorite along with molybdenite, sulfides (e.g., pyrite, pyrrhotite) and oxides (e.g., magnetite, ilmenite). Detailed study of thin sections in optical microscope and BSE images as well as results of EMPA revealed three distinct mineral assemblages - richterite + forsterite (RF) assemblage (Rht + Fo + Cal ˃ Dol ˃ Phl + Di), Na rich actinolite + diopside (AD) assemblage (Di + Act + Rht + Cal ˃ Phl) and magnesio-hastingsite + diopside (HD) assemblage (Mhst + Di + Cal ˃ Ab + Phl). The distinct amphibole species found within the individual assemblages exhibit complex textural relations and crystallized in several prograde and retrograde stages. The following amphibole species were recognized in the individual assemblages: RF - (richterite > ferri-winchite > tremolite, edenite), AD - (actinolite > ferri-winchite; richterite > ferri-katophorite; magnesio-riebeckite), HD - (magnesio-hastingsite; ferri-winchite, actinolite). They differ especially in Mg/(Mg + Fetot) ratio and concentrations of F. Diopside contains up to 17 mol. % of the aegirine component and albite is Fe, Ba-enriched (≥ 0.69 wt. % BaO and ≥ 0.50 wt. % Fe2O3tot). The composition of amphiboles and pyroxenes indicates the alkaline environment of their formation; unusually high Fe2O3 contents in albite plagioclase have known counterparts in alkaline pegmatites and some carbonatite dykes. The following options of potential origin of the carbonatite-like marble from Bližná are discussed: (i) metacarbonates potentially with Na- and Na,Ca-carbonates and sulfate admixture; (ii) admixture of alkaline volcanodetritic component during carbonate sedimentation; (iii) metamorphosed carbonatites enclosed in ordinary sedimentary metacarbonate; (iv) Na-rich metasomatites characterized by mineral assemblages with Na,Fe,F-enriched amphiboles, diopside with high aegirine component and albite. With regard to the observed mineral assemblages, textures and composition of minerals, we can exclude (i) marine evaporates, whereas the other options (ii), (iii) and (iv) are, in general, possible. The amphiboles observed in the Bližná carbonatite-like marble are unique within the Bohemian Massif and distinctly different from amphiboles found in metacarbonates with evaporite component. ]]> Original paper
<![CDATA[ Origin of V-Cr-Ti-mineralization in thermally overprinted metal-rich black shales from the Teplá-Barrandian Unit (Bohemian Massif) and implications for metal remobilization during metamorphism ]]> Veselovský F, Pašava J, Pour O, Ackerman L; Vol. 66, issue 4, pages 263 - 275
We present a detailed study of geochemical composition and ore mineralogy of black shales from Chynín, Czech Republic, representing Ediacaran organic matter-rich sediments, which were subject to regional and contact metamorphism. They are part of the Blovice Accretionaly Complex (BAC) in the Teplá-Barrandian Unit (TBU) and are located close to the contact with the Central Bohemian Pluton (CBP). The black shales were encountered with metasilicites, metabasalts, and basic tuffitic rocks in the CHY-2 drill hole (250 m deep) and are regionally associated with hornfels bodies. The geochemistry of these shales indicates that they correspond to metal-rich black shales deposited under strongly reducing conditions (TOC/P molar > 100, high Mo and U values). On the other hand, the lack of a positive link between TOC and redox-sensitive metals (e.g., V, U, Cr, Ni, Mo) and their generally negative correlation with sulfur indicate important late-stage metal and sulfur remobilization. This is reflected in the mineralogical composition of the shales, which documents a thermal event in their history. Abundant framboidal pyrite (pyrite I) was recrystallized into coarse aggregates (pyrite II), locally accompanied by chalcopyrite, sphalerite, and rare molybdenite, pentlandite and breithauptite. Abundant pyrrhotite formed there due to selective desulfurization of pyrite I and II during the contact metamorphism. Locally, this process was also accompanied by the replacement of pyrrhotite by V-Cr-O (karelianite - V2O3 and eskolaite - Cr2O3, mostly with dominant karelianite end-member) and Ti-V-O (vanadium rutile, schreyerite - V2Ti3O9 and a phase with the theoretical composition V4Ti3O12, yet unknown to the mineralogical system). Vanadium-Cr-Ti elemental associations reported from different localities of Neoproterozoic metal-rich black shales, metal-rich black shales, and (meta)silicites in TBU indicate similar sources of these elements but different conditions of their accumulation. ]]> Original paper