Ordonezite from the Theodoso Soto Mine, Sapioris, Durango, Mexico: New data and structure refinement
A new occurrence of the rare mineral species ordonezite has been found at the Theodoso Soto tin mine, near Sapioris, Durango, Mexico. The average composition of the samples is (Zn 0.98 Fe 0.02 ) Σ1.00 Sb 2.00 O 6 ; the core of the crystals is slightly richer in Fe than the rim. The mineral is uniaxial (+), with all n greater than 2.30 (n calc is 2.38 at 589 nm); D obs 6.66 g/cm 3 , D calc 6.67 g/cm 3 . It is isostructural with ferrotapiolite, with a 4.668(2), c 9.269(6) A (from powder-diffraction data), space group P4 2 /mnm, and is twinned on {103}. Its crystal structure, refined to R=4.1, wR=4.3% using 163 observed reflections, is fully cation-ordered.
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