Discovery of "Meteoritic" Layered Disulphides ACrS(2) (A = Na, Cu, Ag) in Terrestrial Rock

For the first time, chromium disulphides, known from meteorites, such as caswellsilverite, NaCrS2; grokhovskyite, CuCrS2; and a potentially new mineral, AgCrS2, as well as the products of their alteration, such as schollhornite, Na0.3CrS2 center dot H2O, and a potentially new mineral with the formula {Fe-0.3(Ba,Ca)(0.2)} CrS2 center dot 0.5H(2)O, have been found in terrestrial rock. Layered chromium disulphides were found in unusual phosphide-bearing breccia of the pyrometamorphic Hatrurim Complex in the Negev Desert, Israel. The chromium disulphides belong to the central fragment of porous gehlenite paralava cementing altered host rock clasts. The empirical formula of caswellsilverite is (Na0.77Sr0.03Ca0.01)(sigma 0.81)(Cr0.793+Cr0.184+V0.013+ Fe-0.01(3+))(sigma 0.99)S-2 center dot 0.1H(2)O, and the end-member content of NaCrS2 is 76%. It forms single crystals in altered pyrrhotite aggregates. Grokhovskyite has the empirical formula {Cu0.84+Fe0.103+Ca0.06 Na-0.01 Sr0.01Ba0.01}(sigma 1.03)(Cr-0.94(3+) Fe-0.05(3+) V-0.05(3+))(sigma 1.00)S-2 center dot 0.35H(2)O, and the CuCrS2 end-member content is 75-80%. A potentially new Ag-bearing chromium disulphide is characterised by the composition (Ag0.89Cu0.07)(sigma 0.96)(Cr-0.98 Fe0.03V0.01Ni0.01)(sigma 1.04)S-2. Caswellsilverite, grokhovskyite and AgCrS2 form in gehlenite paralava at high temperatures (near 1000 degrees C) and low pressure under reducing conditions. The structure of the layered chromium disulphides, MCrS2, is characterised by the presence of hexagonal octahedral layers (CrS2)(1-), between which M-sites of the monovalent cations Ag, Cu and Na set. A low-temperature alteration of the layered chromium disulphides, when schollhornite and {Fe-0.3(Ba,Ca)(0.2)}CrS2 center dot 0.5H(2)O form, is reflected in the composition and structural modification of the layer with monovalent cations, whereas the octahedral layer (CrS2)(1-) remains unchanged.