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[ Stalactitic rhodochrosite from the 25 de Mayo and Nueve veins, Capillitas, Catamarca, Argentina: Physical and chemical variations ]]> Florencia Marquez-Zavalia M, Craig JR; Vol. 67, issue 3, pages 209 - 227
Capillitas is an epithermal vein-type deposit in Argentina known for its mineralogical diversity, with more than one hundred and twenty described minerals, including five new species, and for the presence of banded and stalactitic rhodochrosite. Stalactites occur as single or combined cylinders of different sizes, from a few cm to 1.36 m in length and diameters up to 8 cm. Their cross-sections may show diverse aspects: from simple concentric banding to more intricate textures, whereas their external surface can be smooth, with undulations or with a poker-chip-like texture. The color of the stalactites varies from white to raspberry pink, with occasional brown bands toward the edges corresponding to a variety of rhodochrosite called “capillitite”. The contents of MnO range from 27.50 to 61.71 wt. % as it may be significantly replaced by CaO, FeO, ZnO and MgO. Replacements are reflected in the various shades of pink and brown displayed by this mineral. The different substitutions in the pink specimens exert only a minor influence on the unit cell parameters, whereas, in the brown variety, their size is significantly smaller with average values for pink rhodochrosite (n = 24): a 4.776 Å, c 15.690 Å and a cell volume of 310.3 Å3, whereas, “capillitite” unit-cell parameters (n = 7) are: a = 4.739, c = 15.558 with a unit-cell volume of 302.6 Å3. Conditions of formation of the banded rhodochrosite of the 25 de Mayo vein, obtained from fluid inclusions data, indicate temperatures of 145 ° to 150 °C and salinities of up to 4 wt. % NaCl(eq). The formation of the stalactites is explained by the infiltration of epithermal aqueous liquid, oversaturated with Mn and bicarbonate, into a transiently vapor-filled, isolated cavity. ]]> Original Paper
<![CDATA[ Pertoldite, trigonal GeO2, the germanium analog of α-quartz: a new mineral from Radvanice, Czech Republic ]]> Žáček V, Škoda R, Laufek F, Sejkora J, Haifler J; Vol. 67, issue 3, pages 229 - 237
The new mineral pertoldite was found in a burning waste dump of abandoned Kateřina colliery at Radvanice near Trutnov, Hradec Králové Department, Czech Republic. The dump fire started spontaneously before 1980 and no anthropogenic material was deposited there. The determination of pertoldite as a natural analog of synthetic trigonal α-GeO2 is based on its chemical composition, X-ray powder diffraction data, and Raman spectroscopy. Pertoldite occurs as white to brownish aggregates resembling cotton tufts, up to 1 mm in size, composed of acicular crystals up to ˜1 μm thick and up to 1 mm in length. Individual crystals are distorted, resembling textile fibers. Pertoldite was formed by direct crystallization from hot (400-500 °C) gasses containing Cl and F as transporting agents at a depth of 40-60 cm under the surface of a burning coal mine dump. It nucleated as a thin, delicate crust on a chip of siltstone together with multi-component aggregates of galena, stibnite, bismuthian antimony, greenockite, and bismuth. The ideal formula of pertoldite, GeO2, requires 100 wt. % GeO2. Germanium is partially substituted by silica (2.33-5.67 wt. % SiO2), the extent of Ge1Si-1 substitution is limited to 0.03-0.09 apfu Si, and the empirical formula ranges between (Ge0.91-0.97Si0.03-0.09)Σ1.00O2. Pertoldite is trigonal, P3121 or P3221, a = 4.980(5) Å, c = 5.644(4) Å, with V = 121.2(2) Å3 and Z = 3. The strongest reflections of the powder X-ray diffraction pattern [d (Å)/I (hkl)] are: 4.315/44(100), 3.425/100(101,011), 2.490/31(110), 2.360/41(012,102), 1.867/31(112), 1.4179/31(023,203), 1.4124/37 (122,212). The crystal structure of pertoldite is based on corner-sharing [GeO4] tetrahedra forming a three-dimensional network similar to that of α-quartz. Pertoldite is named after Zdeněk Pertold (1933-2020), professor of economic geology at the Faculty of Sciences, Charles University in Prague. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (number 2021-074) and the holotype specimen is deposited in the collections in the Department of Mineralogy and Petrology, National Museum in Prague, under the catalogue number P1P 31/2021. ]]> Original Paper
<![CDATA[ Morphology and Raman spectral parameters of Bohemian microdiamonds: implications to elastic geothermobarometry ]]> Jakubová P, Kotková J, Wirth R, Škoda R, Haifler J; Vol. 67, issue 3, pages 239 - 257
In this work, we combine the morphology and internal structure of northwestern Bohemian microdiamonds with their Raman spectral parameters to describe and understand their relationship. We evaluate our data according to the theory of elasticity and discuss implications for elastic geothermobarometry of diamond inclusions in garnet. We conclude that microdiamonds enclosed in kyanite, garnet and zircon differ in morphology and internal structure depending on the type of the host rock and host phase. Single crystal diamond octahedra in kyanite in the acidic gneiss show predominantly Raman shift towards higher wave numbers (upshift), while single and polycrystalline diamonds enclosed in garnet and zircon in the intermediate garnet-clinopyroxene rock yield more variable Raman shift including a shift towards lower wavenumbers (downshift). This is consistent with closed boundaries between diamond and kyanite observed using FIB-TEM, while interfaces between diamond and garnet or zircon are commonly open. Moreover, higher variability in the Raman shift in diamond hosted by garnet or zircon may be caused by complex internal structure and the presence of other phases. At the same time, a diamond in kyanite features relatively high full-width-at-half-maximum (FWHM) due to the anisotropy of thermal contraction, which is reflected by the plastic deformation of diamond mediated by dislocation glide at T ≤ 1000 °C. The entrapment pressure (Ptrap) for diamonds in garnet was calculated using elastic geobarometry to test its compatibility with the existing peak pressure estimated by conventional thermobarometry. The “downshifted” diamonds exhibit entrapment pressures of 4.8±0.14 and 4.99±0.14 GPa at an entrapment temperature of 1100 °C, using unstrained reference diamond from the literature and own measurements, respectively. This is consistent with the earlier estimates and the elastic theory and does not require any elastic resetting suggested to account for the reported upshift in garnet. Our data suggest that the upshift in diamond hosted by garnet is related to the proximity of other diamond grains. We conclude that the use of diamond inclusions in elastic barometry should be backed by careful evaluation of its internal structure and associated phases and restricted to isometric monocrystalline diamond grains not occurring in clusters as required by the method. ]]> Original Paper
<![CDATA[ Sample preparation and chromatographic separation for Sr, Nd, and Pb isotope analysis in geological, environmental, and archaeological samples ]]> Erban Kochergina YV, Erban V, Hora JM; Vol. 67, issue 3, pages 259 - 271
In countless modern geochemical studies, diverse biological and geologic samples are analyzed for Sr, Nd, and Pb isotopic composition. Such heterogeneity presents challenges for a “one-size-fits-all” approach to sample preparation, necessitating customization of sample preparation and chromatographic separation methods. We present (1) digestion techniques for low-Nd silicates, carbonatites, carbonates, water, plant and wood material, organic soils, aerosols collected via filtration, as well as archaeological samples (alloys, teeth, and bones) (2) a column chromatographic approach for samples with low concentrations (large amounts of a matrix) and (3) method verification via replicate analyses of a wide variety of isotopic standards. ]]> Original Paper