We have undertaken a study of the hydrated hydroxyl carbonate mineral, hydromagnesite, from the burnt mine dump of the Mayrau coal mine at Vinařice near Kladno, central Bohemia (Czech Republic). Hydromagnesite occurs as rich white crystalline coatings up to several cm2 in size formed by spherical to hemispherical aggregates up to 0.5 mm in size. The semi-quantitative chemical analyses of hydromagnesite confirmed presence of Mg and O. Hydromagnesite is monoclinic, the space group P21/c, with the unit-cell parameters refined from X-ray powder diffraction data: a 10.096(3), b 8.934(2), c 8.366(3) Å, β 114.471(19)° and V 686.8(4) Å3. Raman spectroscopy documented the presence molecular water, hydroxyl groups and carbonate units in its crystal structure.
Argentopyrite in association with miargyrite was found on an archived specimen probably originating from the Lill shaft, Černojamské deposit (central Bohemia, Czech Republic). It was found as small wheel-like crystal aggregates up to 1 mm in size partly replaced by small crystals of pyrite. The original colour is bronze-brown but it tarnished black. Apart from main elements Ag, Fe and S, it contains minor Cu and Hg (up to 0.04 apfu) and Te. Its empirical formula (4 analyses) on the basis of 6 apfu corresponds to (Ag0.97Cu0.04)Σ1.01Fe1.93S3.06. The predominant ore mineral on the specimen is miargyrite with empirical formula Ag0.99Sb1.02S1.99 in the form of crystals up to 7 mm in size. Its colour is black and has a typical cherry-red streak. The associated minerals include siderite, sphalerite, quartz, carbonates, baryte, pyrite and possible millerite.
An unusual Mn-mineralization was found in the material from mine dump of the abandoned mine Štěstí s radostí (Glück mit Freuden) located near Ryžovna (Boží Dar), Krušné hory Mountains, Bohemia (Czech Republic). Manganite forms abundant aggregates up to 1 cm in size and veins up to 0.5 cm thick, overgrowing fragments of earlier quartz. It is usually fine-grained, the margins of the aggregates and veins are formed by tabular crystals up to 1 mm in length arranged perpendicular to the surface of the aggregates and veins. It is opaque, dark gray to blackish gray, with an earthy, silky to vitreous lustre. Manganite is monoclinic, space group P21/c, with the unit-cell parameters refined from X-ray powder diffraction data: a 5.3071(6), b 5.2743(4), c 5.3071(6) Å, β 114.456(6)° and V 135.23(3) Å3. Its chemical analyses (mean of 12 spots) correspond to the empirical formula (Mn0.97Al0.01Si0.01P0.01)Σ1.00O1.03(OH)0.97. The youngest component of the gangue is rhodochrosite, which forms aggregates up to 5 mm in size, which fill the cavities among the manganite veins. More rarely, it also forms in the cavities hemispherical aggregates up to 2 mm in size with a finely crystalline surface. In one cavity, a group of well-developed rhodochrosite crystals up to 0.25 mm in size was observed. Rhodochrosite is yellow-gray to gray, with a pink tints, it is translucent and exhibits a greasy to vitreous lustre. It is trigonal, space group R-3c, with the unit-cell parameters refined from X-ray powder diffraction data: a 4.7771(2), c 15.6687(8) Å and V 309.66(2) Å3. Its chemical composition (mean of 7 spot analyses) corresponds to the empirical formula (Mn0.95Mg0.03Ca0.02)Σ1.00CO3.
A rare mineral branchite, ideally C20H34, was discovered at the Cigeľ mine, Handlová coal deposit, Prievidza Co., Trenčín Region, Slovakia. This is the first occurrence of this relatively rare mineral in Slovakia. It occurs as colourless to white coarse crystalline fillings consisting of individual flattened aggregates up to 1 cm in size, developed in fractures of coal. The unit-cell parameters of branchite from the Cigeľ mine (for the triclinic space group P1) refined from the PXRD data are: a 11.4146(8), b 20.9692(13), c 7.4090(6) Å, α 93.945(5), β 100.732(6), γ 80.508(5)° and V 1717.2(2) Å3. The occurrence of branchite in the material from the Cigeľ mine was also confirmed by Raman and infrared spectro- scopy, and the tentative assignment of the Raman spectrum is provided in this paper.
Dawsonite, a rare sodium aluminium hydroxycarbonate, NaAl(CO3)(OH)2, was identified in material from the Tuchlovice coal mine dump in the western part of the Kladno Coal District (central Bohemia, Czech Republic). This occurrence represents the second confirmed finding of dawsonite in the Czech Republic, following its previously documented occurrence at the Slaný locality. The studied material consists of Proterozoic shales and associated quartz veins affected by superimposed hydrothermal and late-stage mineralization. Dawsonite occurs in small fractures and cavities within the shales and thin quartz veins, commonly in association with dolomite and pyrrhotite. It forms snow-white spherulitic aggregates and clusters reaching up to 1 cm in size. Dawsonite is orthorhombic, space group Imma, with the unit-cell parameters refined from X-ray powder diffraction data: a 6.7523(6), b 5.5812(5), c 10.4261(8) Å and V 392.92(4) Å3. The ED and WD analyses show substantial Na and Al contents and Raman spectrum confirms presence of (OH) and (CO3) groups in studied mineral. The mineral assemblage and host-rock characteristics suggest formation under low-temperature conditions within a CO2-rich, alkaline fluid regime comparable to that inferred for the Slaný occurrence. Due to the extensive recultivation of the dump in 2007 - 2011, further mineralogical investigation of the locality is now effectively precluded. The Tuchlovice occurrence thus provides additional insight into the distribution and paragenesis of dawsonite within the Kladno Coal Basin and confirms its rare occurrence in the Czech Republic.
