Laffittite, AgHgAsS ₃ ; crystal structure and second occurrence from the Getchell Mine, Nevada

Smithson. Inst., Dep. Miner. Sci., Washington, DC, United States

Laffittite, AgHgAsS ₃ , is monoclinic, space group Aa, a = 7.732(3), b = 11.285(7), c = 6.643(4)Aa, beta = 115.16(3) degrees , Z = 4. The strongest lines in the X-ray powder pattern are 3.512(100)(200), 3.202(78)(031,1 (super -) 31), 3.015(69)(002), 2.685(67)(2 (super -) 31), 1.898(29)(1 (super -) 33,2 (super -) 33, 2.136(18)(231,3 (super -) 31), 3.633(16)(111), 1.889(14)(4 (super -) 11). Hydrothermally synthesized at 350 degrees C under 10,000 psi pressure for 140 hours. The crystal structure of laffittite is a superstructure based upon the PbS structure. Metal-sulfur bonds form a hexagonal ring of one formula unit; the rings link to each other by sharing all edges forming a sheet parallel to (100); the sheets link up and down by Hg-S and Ag-S bonds to form a three-dimensional network. The structure is closely related to that of marrite, PbAgAsS ₃ .--Modified journal abstract.

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