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Description and crystal structure of yvonite, Cu(AsO 3 OH)2H 2 O

1998; Mineralogical Society of America; Volume: 83; Issue: 3-4 Linguagem: Inglês

10.2138/am-1998-3-423

1945-3027

Halil Sarp, Radovan Černý,

Radioactive element chemistry and processing

Yvonite, Cu(AsO 3 OH)2H 2 O, was found in the Salsigne mine near Carcassone (Aude, France).It forms aggregates or radiating spherules consisting of individual crystals (maximal size 0.3 ϫ 0.15 ϫ 0.06 mm) of turquoise blue color.They are elongated in c, flattened on (010), and have a perfect cleavage on (100).The mineral is triclinic, P1, a ϭ 7.632(3), b ϭ 11.168(3), c ϭ 6.020(3)A ˚, ␣ ϭ 89.32(3), ␤ ϭ 86.55(5), ␥ ϭ 74.43(3)Њ, V ϭ 493.4(3)A ˚3, Z ϭ 4, D meas ϭ 3.20(2) g/cm 3 , and D calc ϭ 3.22(1) g/cm 3 .Mohs hardness 3.5-4.Luster vitreous transparent, streak blue; optically biaxial (-) with ␣ ϭ 1.615(2), ␤ ϭ 1.660(2), and ␥ ϭ 1.700(2) at 589 nm; 2 V obs ϭ 82(2)Њ, 2 V calc ϭ 84(1)Њ.Pleochroism weak with Z ϭ blue, Y ϭ light blue, and X ϭ light blue to colorless.Associated minerals: geminite, lindackerite, arsenopyrite, native bismuth, chalcopyrite, and pushcharovskite.The crystal structure was solved by direct methods (MoK␣ radiation) and refined using 1429 observed unique reflections to R ϭ 0.069, R w ϭ 0.043.There are two symmetrically independent distorted CuO 5 (H 2 O) octahedra in the structure.They share edges and form cis [CuO 3 (H 2 O)] chains parallel to [001].Two symmetrically independent distorted AsO 3 (OH) tetrahedra cross-link these chains to form sheets parallel to (100).Two symmetrically independent H 2 O molecules are located between the sheets, which are linked by a network of hydrogen bonds, accounting for the perfect cleavage of yvonite.The mineral is structurally related to geminite, Cu(AsO 3 OH)(H 2 O), and fluckite, CaMn[(AsO 3 OH)(H 2 O)] 2 .FIGURE 1. Scanning electron microscope photograph of yvonite crystals, elongated in the c axis direction and flattened on (010).Bar scale is 10 m. * Loss upon heating.