The structure of natural carlfriesite, given by Williams and Gaines (1975) as H4Ca(TeO3)3, was determined by single-crystal standard X-ray procedures. The least-squares refinement for 595 observed reflections resulted in a conventional reliability index R = 0.027 (with anisotropic temperature factors for Ca and Те and isotropic for O). The cell content obtained is Ca4Te12O32, with one third of the Те atoms in octahedral coordination, as characteristic for Te(VI), and the rest in the usual one-sided coordination of Te(IV). Carlfriesite was synthesized by the hydrothermal treatment of a stoichiometric mixture of TeO2, Te(OH)6, and CaO at 150-230°C.

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