Tivanite, a new oxyhydroxide mineral from Western Australia, and its structural relationship to rutile and diaspore

Tivanite, V_4.37Fe_0.14Ti_3.49O_11.49(OH)_4.51 (ideal VTiO₃OH), is a new mineral species that has been found in the “green leader” gold lodes at Kalgoorlie, Western Australia. Is is monoclinic with space group P2₁/c, a = 7.494(5), b = 4.552(4), c = 10.005(8)Å, β = 129.79(2)°, Z = 1. The strongest powder diffraction lines (calculated) are 3.880(100)(111), 2.795(94)(211), 2.636(69)(113), 1.683(31)(224), 1.693(30)(122), 3.917(25)(011).

Tivanite occurs as minute multiply twinned crystals in quartz. Associated minerals are vandian muscovite and nolanite. Tivanite is black with a submetallic luster, lacks internal reflections, is moderately anisotropic, and has a specific gravity of 4.17 (calc.). Reflectivity values are 470 nm 16.8%, 546 nm 17.4%, 589 nm 17.7%. The microhardness is VHN 650 under a 50 g load.

The structure has been determined and refined to R = 0.12 using intensities collected for a multiply twinned crystal by the Weissenberg technique, using CuKα radiation. The structure is based on an ordered occupation by V³⁺ and Ti⁴⁺ of half of the octahedral sites in a hexagonal closest-packed anion array. It can be described as an ordered 1:1 intergrowth of TiO₂ with a rutile-type structure and VOOH with a diaspore-type structure.