Zincalstibite, a new mineral, and cualstibite: Crystal chemical and structural relationships

Zincalstibite, a new mineral occurring within the cavities of marble of the Apuan Alps, Tuscany,, has chemical formula Zn2AlSb(OH)12, space group P 3, a = 5.321(1), c = 9.786(2) Å. It is associated sub-millimeter tufts of white crystals of mimetite and sub-millimetric stalactite aggregates of and an amorphous copper-silicate phase (possibly crisocolla). The crystals are trigonal prismatic, forms {110}, {001}, elongated [001], generally less than 10 × 10 × 40 ÷ 50 μm, with few larger. They are colorless, transparent, with vitreous luster, white streak and {001} cleavage. The reß ections are [(hkl), d (Å), Irel]: (002), 4.904, 100; (100), 4.620, 35; (101), 4.179, 57; (103,110), 2.669, 31; (112, 11 2), 2.343, 88; (114, 11 4), 1.805, 57. Zincalstibite is structurally related to cualstibite, evidenced by the structural determinations and reÞ nements we present for both the minerals. are built up by layers of isolated Sb(OH)6 octahedra alternating along c with trioctahedral layers, contain Zn and Al cations and Cu and Al cations in zincalstibite and cualstibite, respectively. In the ordering of Al and Cu within these trioctahedral layers results in a supercell, with acual =9.150(2) Å ≈ √3 azinc. The name of zincalstibite is related to its chemical composition and points to its with cualstibite. Both the mineral and its name were approved by the IMA Commission New Minerals and Mineral Names (IMA 1998-033).