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Xenotime-(Gd), ideally GdPO4, is a new mineral of the xenotime group. It was discovered at the Zimná Voda REE–U–Au occurrence near Prakovce, Western Carpathians, Slovakia. It forms rare crystal domains (≤20 μm, usually ≤10 μm in size) in Gd-rich xenotime-(Y) crystals (≤100 μm in size), in association with monazite-group minerals, uraninite, fluorapatite and uranyl arsenates–phosphates. The hydrothermal REE–U–Au mineralisation occurs in a quartz–muscovite vein, hosted in Palaeozoic phyllites near exocontact with Permian granites. The density is 5.26 g/cm3, based on calculated average empirical formula and unit-cell parameters. The average chemical composition (n = 6) measured by electron microprobe is as follows (wt.%): P2O5 30.1, As2O5 0.5, SiO2 0.2, UO2 0.3, Y2O3 15.7, (La, Ce, Pr, Nd)2O3 0.5, Sm2O3 5.7, Eu2O3 1.4, Gd2O3 29.2, Tb2O3 3.9, Dy2O3 10.4, Ho2O3 0.4, (Er, Tm, Yb, Lu)2O3 2.1, (Ca, Fe, Pb, Mn, Ba)O 0.1, total 100.5. The corresponding empirical formula calculated on the basis of 4 oxygen atoms is: (Gd0.37Y0.32Dy0.13Sm0.08Tb0.05Eu0.02Er0.01Tm0.01Nd0.01...)Σ1.01(P0.98As0.01Si0.01)O4. The empirical formula of the Gd-richest composition is: (Gd0.38Y0.31Dy0.13Sm0.08Tb0.05Eu0.02Er0.01Nd0.01Ho0.01...)Σ1.01(P0.98As0.01Si0.01)O4. The ideal formula is GdPO4. The xenotime-type structure has been confirmed by micro-Raman spectroscopy and a Fast Fourier-Transform pattern using HRTEM. Xenotime-(Gd) is tetragonal, space group I 41/ amd , a = 6.9589(5) Å, c = 6.0518(6) Å, V = 293.07(3) Å3 and Z = 4. The new mineral is named as an analogue of xenotime-(Y) and xenotime-(Yb) with Gd dominant among the REE. The middle REE enrichment of xenotime-(Gd) is shared with the associated monazite-(Gd) and Gd-rich hingganite-(Y). This exotic REE signature and precipitation of Gd-bearing minerals is a product of selective complexing and enrichment in MREE in low-temperature hydrothermal fluids by alteration of uraninite, brannerite and fluorapatite on a micro-scale. The existence of xenotime-(Gd) and monazite-(Gd) is the first naturally documented dimorphism among REE phosphates. In addition, xenotime-(Gd) is only the third approved Gd-dominant mineral, after lepersonnite-(Gd) and monazite-(Gd). [ABSTRACT FROM AUTHOR]

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Calc–alkaline lamprophyres are known from several localities in the Malá Fatra Mountains. They form dykes (0.5–3 m) of varying degree of alteration that have intruded the surrounding granitoid rocks which are often incorporated xenoliths. Clinopyroxenes (diopside to augite), amphiboles (kaersutitic), biotites (annite) and plagioclases are major primary minerals of the dykes, accessory minerals include apatite, ilmenite, rutile, pyrite, chalcopyrite, and pyrrhotite. Apatite has a relatively low F, but increased Cl content compared to typical apatite from lamprophyres or magmatic apatite from granitic rocks in the Western Carpathians. The chemical composition of the lamprophyres indicates their calc–alkaline character, but affinity to alkaline lamprophyres is suggested by the Ti enrichment in clinopyroxene, amphibole and biotite. According to modal classification of the minerals, the studied rocks correspond to spessartite. The differences in the chemical composition of the rocks (including Sr and Nd isotopes) probably result from the contamination of primary magma by crustal material during magma ascent. The age of the lamprophyres, based on U/Pb dating in apatite, is 263.4 ± 2.6 Ma.

Various chrysoberyl varieties (non‐phenomenal chrysoberyl, alexandrite and cymophane) are gemstones of high demand; therefore, they are subjected to numerous substitutions by other materials and synthetic analogues. To address this issue, non‐destructive methods for studying gemstones are highly sought after. Raman spectroscopy is one of the most suitable non‐destructive methods for studying gemstones as it requires no sample preparation and does not leave any price‐reducing signs on the gemstone surface. The research is focused on Raman spectroscopy application on chrysoberyl identification, differentiation between its varieties, inclusion analysis, and detection of synthetic analogues and imitations. The alexandrite variety can be identified by its broad luminescence band that ranges from 640 to 790 nm (15 625–12 658 cm−1). Synthetic alexandrite has sharper and more intensive bands on the luminescence spectrum, especially 690 and 696 nm (14 492–14 367 cm−1). Rutile inclusions can be distinguished by a broad band 580–640 cm−1 in the Raman spectrum. Imitations of chrysoberyl represented by corundum and colour‐changing spessartine was also identified. The orientation of faceted stones can also be determined by specific bands present in the Raman spectrum. [ABSTRACT FROM AUTHOR]

A hydrothermal quartz vein with REE-U-Au mineralization in the Zimná Voda (Gemeric Unit, Western Carpathians, Slovakia) is associated with contact metamorphism between Permian granites and host phyllites and metaquartzites. It contains unique REE minerals of the monazite and xenotime groups. Monazite-(Ce), monazite-(Nd), monazite-(Sm), and Gd-dominant monazite ["monazite-(Gd)"], along with xenotime-(Y) to Gd-dominant xenotime ["xenotime-(Gd)"] and Gd-rich hingganite-(Y) show heterogeneous compositions and reflect a strong fractionation trend toward the enrichment of MREE (Sm to Dy), particularly Gd. Here, the gadolinium abundance reported in "monazite-(Gd)" (≤23.4 wt% Gd2O3) and Gd-rich xenotime-(Y) to "xenotime-(Gd)" (≤28.7 wt% Gd2O3) and accompanied by Gd-rich hingganite-(Y) (≤15.8 wt% Gd2O3), is among the highest Gd concentrations ever reported in natural minerals. The Gd-richest compositions show the following formulas: (Gd0.31Sm0.24 Nd0.15Ce0.10La0.05Dy0.03Y0.03...)0.98PO4 ["monazite-(Gd)"], (Gd0.36Y0.32Dy0.13Sm0.08Tb0.05...)0.98 (P0.96As0.04)1.00O4 ["xenotime-(Gd)"] and (Y0.71Gd0.43Dy0.23Sm0.22Tb0.06Er0.04Nd0.06...Ca0.06)1.96 ( ◻ 0.87 Fe 0.13 2 +) 1.00 (B e 1.82 B 0.18 ) 2.00 (S i 1.90 A s 0.10 ) 2.00 O 8 (O H 1.70 O 0.30 ) 2.00 [hingganite-(Y)]. The MREE-rich monazites, xenotimes, and hingganite-(Y) precipitated in response to the alteration of primary uraninite, brannerite, and fluorapatite by low-temperature hydrothermal fluids of heterogeneous compositions on a microscale. These are responsible for the strong enrichment of individual MREE, especially Gd in the secondary minerals. This is accompanied by the advancing development of the W-type tetrad effect on REE through monazite species. The substantial incorporation of Gd into both REE-selective monazite and xenotime structures that are accompanied by LREE vs. HREE segregation indicates the possibility of differently sized REE3+ miscibility in REEPO4 solid solutions, as well as the stabilization of the Gd-rich orthophosphate structure by substitution of the remaining A-site cations with smaller HREE+Y in the xenotime-type, and/or larger LREE in the monazite-type structure. [ABSTRACT FROM AUTHOR]

A pavement brick taken from a Romanesque part of the church in Pác, in the Trnava County, Slovakia, was investigated by x-ray diffraction analysis (XRD) and thermal analyses as differential thermal analysis (DTA), thermogravimetry (TG) and thermodilatometry (TD). It was found that the brick contained dehydroxylated illitic clay, calcite and quartz. As revealed, dehydroxylation was completely finished and no redehydroxylation was observed. Partial decomposition of calcite was also found. The estimated firing temperature is between 600 °C and 700 °C.

Tourmalinites occur in early-Paleozoic metamorphic rocks of the Gemeric Unit near Zlatá Idka village, Western Carpathians, eastern Slovakia. Tourmaline compositions, analyzed with the electron microprobe, include a wide range of tourmaline species. Tourmaline in tourmalinites from Zlatá Idka is compositionally variable, with the dominant substitution Mg-Fe2+ consistent with prevalent schorl-dravite compositions and their fluor- and oxy-dominant counterparts - fluor-schorl, fluor-dravite, oxy-schorl and oxy-dravite. Portions of tourmaline are enriched in Ca in the form of the fluor-uvite and magnesio-lucchesiite components. A subset of the compositions has Ti > 0.25 atoms per formula unit (apfu) and corresponds to the hypothetical “magnesio-dutrowite”, Mg-dominant analogue of dutrowite. In addition, some of the tourmalines are X-site vacant and classified as foitite. The crystal chemistry of tourmaline is complex and influenced by several exchange mechanisms, including Mg(Fe)-1, Al□(Mg,Fe)-1Na-1, AlO(Mg,Fe)-1(OH)-1 (Mg,Fe)CaAl-1Na-1, MgCaOAl-1□-1(OH)--1, Ti0.5O(Fe,Mg)-0.5(OH)-1 and TiMg(Al)-2 substitutions. In general, tourmalines in all samples usually have oscillatory-zoned dravitic cores and schorlitic rims (Tur I). However, in ZLT-4 and ZLT-6 samples, some crystals have secondary Mg-dominant and Ca-enriched overgrowths (Tur II), partially replacing Tur I. Tourmalinites were most likely produced by regional or contact metasomatic processes, likely due to the intrusion of the Permian Poproč granitic massif. Origin of tourmalinites likely results from the flow of late-magmatic to early post-magmatic B,F-rich fluids from the granite intrusion into adjacent metamorphic rocks. The tourmaline crystallization and its resulting chemical composition were controlled by both the metapelitic host rock and the granitic intrusion; the Mg-rich cores of the Tur I are most likely compositionally related to the metapelitic host rock, whereas later schorlitic to foititic compositions in rims suggest origin due to the intrusion-triggered fluid flow. The significant changes and oscillations of tourmaline zoning imply a dynamic, unstable fluid regime. The late Ca-rich Tur II could result from subsequent metasomatic processes associated with the alteration of host-rock minerals. [ABSTRACT FROM AUTHOR]