Škáchaite, CaCo(CO3)2, a New Member of the Dolomite Group, from the Brod Deposit Near Příbram, Czech Republic

Skachaite (IMA2022-143) is a new mineral species discovered in samples from the hydrothermal vein B117, shaft No. 6 at the Brod deposit of the uranium and base-metal Pribram ore district, central Bohemia, Czech Republic. Skachaite is a Co-dominant member of the dolomite group and forms anhedral grains up to 50 mu m in size and as 20-100 mu m thick growth zones in Skachaite-dolomite crystals as a part of carbonate (dolomite, calcite, siderite, spherocobaltite, ankerite, kutnohorite and minrecordite) gangue, associated with native silver, sulfides and arsenides. & Scaron;k & aacute;chaite is pale to bright pink with vitreous lustre. The Mohs hardness is ca. 3 1/2 -4, similar to other members of the dolomite group. The calculated density is 3.140 g.cm(-3). & Scaron;k & aacute;chaite is optically uniaxial (-); the indices of refraction are omega = 1.741(3) and epsilon = 1.535(3). On the basis of electron-microprobe analyses, its empirical formula is Ca-1.00(Co0.45Mg0.38Ca0.08Fe0.05Mn0.03Zn0.01)(Sigma 1.00)(CO3)(2). The ideal formula is CaCo(CO3)(2), which requires (in wt.%) CaO 25.60, CoO 34.21, CO2 40.19, a total of 100.00. Skachaite is trigonal, R3, with unit-cell parameters a = 4.8177(18), c = 16.093(7) & Aring;, V = 323.5(2) & Aring;(3) and Z = 3. The strongest reflections of the calculated powder X-ray diffraction pattern [d, & Aring;, (I-rel, %) hkl] are: 3.704 (13) 102; 2.896 (100) 104; 2.409 (15) 110; 2.019 (17) 202; 1.812 (19) 10; and 1.792 (16) 116. According to the single-crystal X-ray diffraction data (R-1 = 0.0304 for 94 reflections with [I > 3 sigma(I)]), the crystal structure of Skachaite is isotypic with its Mg-analogue, dolomite. The Raman spectrum of Skachaite, as well as the tentative assignment of observed bands, are given in this paper. The mineral is named in honour of Pavel Skacha, a Czech mineralogist and curator of the mineralogical collection of the Mining Museum Pr & iacute;bram, Czech Republic.