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The beryllium silicate minerals phenakite and bertrandite have been identified in granitic pegmatite dykes of the beryl-columbite subtype of Variscan age (~340−355 Ma), associated with S- to I-type granitic rocks of the Tatric Superunit, Western Carpathians (Slovakia). The two beryllium silicates and associated minerals were characterised by electron microprobe analysis, back-scattered electron petrography and cathodoluminescence imagery, X-ray diffraction and micro-Raman techniques. Phenakite and bertrandite form euhedral-to-anhedral crystals and aggregates in irregular domains and veinlets replacing primary magmatic beryl. A detailed textural study revealed a close genetic association of phenakite and bertrandite with secondary fine-grained quartz, K-feldspar and muscovite. Locally, clay phyllosilicate minerals, (with compositions similar to those of Fe-dominant hydrobiotite, beidellite, nontronite and saponite) occur as the youngest minerals. During the post-magmatic (hydrothermal) stage of the pegmatites, infiltration of aqueous K-bearing fluids at T ≈ 200–400°C resulted in the breakdown of magmatic beryl to secondary assemblages containing phenakite and bertrandite. [ABSTRACT FROM AUTHOR]

The rare Hg-sulfosalt, marrucciite, with ideal formula Hg3Pb16Sb18S46, was found in the Gelnica ore deposit (Spišsko-Gemerské Rudohorie Mts., Slovak Republic). It occurs as acicular crystals up to 0.5 mm in length and fine-grained aggregates up to 1 mm in quartz (+siderite/dolomite) gangue in association with other sulfosalts (zinkenite, scainiite, boulangerite, chalcostibite, bournonite) and cinnabar. It is opaque, dark steel grey to greyish black, sometimes tarnished to a bronze-brown tint, has a dark grey streak with a very weak reddish tint and a metallic luster. Marrucciite is very brittle but thin acicular crystals are flexible. One good cleavage parallel to the elongation of the crystals was observed. The VHN20g microhardness is 85 (69-101) kp/mm² and corresponds to a Moh's hardness ofc. 2; the calculated density is 6.00 g.cm-3. In reflected light, marrucciite is white to greyish white with a weak yellowish tint, distinct bireflectance and white-white grey pleochroism. Under crossed polars, it has distinct anisotropy, with rotation tints in shades of grayish brown and dark brown. Dark red internal reflections were observed only rarely. Marrucciite is monoclinic, space group C2/m with a 48.12( 1 ), b 4.1083(2), c 23.990(5)/Å, β 118.76(2)°, V 4158.(3) ų. Its average composition (electron microprobe data in wt. %) is Cu 0.03, Hg 7.83, Cd 0.02, Fe 0.06, Zn 0.02, Pb 43.13, Sn 0.03, Sb 29.15, Bi 0.12, S 19.71, CI 0.05, total 100.15. The empirical formula on the basis 83 of apfu is Hg2.93(Pb15.63Fe0.08Cu0.04Cd0.02Zn0.02Sn0.02)∑15.81 (Sb17.97Bio0.04)∑18.01(S46.14Cl0.11)∑46.25. The crystal structure of marrucciite from Gelnica contains two Hg positions (6 atoms), 7 Pb positions (28 atoms), 8 Sb positions (32 atoms), two mixed Pb-Sb positions (refined as Pb0.39Sb0.61 and Pb0.61Sb0.39) and 23 S positions (46 atoms). [ABSTRACT FROM AUTHOR]

Granitic pegmatite vein (ca. 15 cm thick) containing Be-minerals occurs in granite from the Sitina tunnel in Bratislava, SW Slovakia. Dark grey quartz, white to dark grey microcline, milky-white albite (partially variety cleavelandite) and muscovite are main minerals of the pegmatite. Accessory minerals include garnet (almandine), chlorite and mica (biotite) and Be-bearing minerals: beryl and phenakite. Beryl shows increased concentrations of Mg (up to 0.35 apfu), Fe (up to 0.14 apfu) and Na (up to 0.48 apfu). Average crystallochemical formula of beryl is following (n=12): Na0.46Be3.00 Al1.52Mg0.32Fe0.12Si6.04O18. The Fe,Mg-rich composition and high c/a lattice ratio (0.9916) indicate a presence of octa-hedral beryl type. Phenakite is a part of younger generation of quartz crossing the beryl crystal. [ABSTRACT FROM AUTHOR]

Native bismuth forms rare aggregates (up to 1 mm across) in quartz core of the beryl-type granitic pegmatite from Bratislava, Švábsky Hill (Malé Karpaty Mts., Slovakia). The pegmatite dike (<1 m thickness) cuts parental Hercynian S-type granites of the Bratislava massif. The bismuth shows homogeneous, nearly end-member composition (only 0.2 wt.% Sb). It is partly replaced by bismite and bismutite along the rims. Native bismuth precipitated during inal hydrothermal stage of the pegmatite crystallization at temperature 250 - 260 °C, whereas supergene bismite and bismutite are products of late oxidation and weathering processes, or low-temperature alteration of the bismuth. [ABSTRACT FROM AUTHOR]

The quartz veins with primary fluorapatite, xenotime-(Y), monazite-(Ce) to monazite-(Nd), uraninite, and secondary florencite-(Ce) and goyazite occur in Lower Devonian metavolcano-sedimentary sequence of the Gelnica Group, Gemeric Superunit, the Central Western Carpathians (eastern Slovakia). They represent an example of hydrothermal REE-U mineralization. Fluorapatite forms parallel bands of columnar crystals (≤ 3 cm) in massive quartz. Monazite- (Ce) to (Nd) shows a near end-member composition with very small amounts of cheralite and huttonite components. Widespread xenotime-(Y) forms colloform aggregates or irregular aggregates in association with fluorapatite and monazite. Uraninite electron-microprobe U-Pb dating gave the average age o f207 ± 2 Ma (n = 16, 2σ), which is consistent with formation of the U mineralization in the Gemeric Superunit (e.g., Kuriskova uranium deposit) during early Alpine hydrothermal activity. [ABSTRACT FROM AUTHOR]