Kimrobinsonite mineral

Cryptocrystalline tantalum-niobium hydroxide-oxide-carbonate mineral with current September 2026 IMA-CNMNC approved formula Ta(OH)3(O,CO3) (expressed in the original paper as (Ta,Nb)(OH)5-2x(O,CO3)_x with x ~ 1.2), status A, and approval number IMA 1983-023. Nickel and Robinson (1985) described the type material (portions deposited at the Government Chemical Laboratories of Western Australia, Perth, National Museum of Victoria, Melbourne, British Museum (Natural History), London, Smithsonian Institution, Washington, and Ecole Superieure des Mines, Paris) from a 3 x 2 x 1.5 cm white friable mass recovered at 14 m depth in a deeply weathered rubellite-bearing granitic pegmatite near Mt. Holland (32 deg 10 min S, 119 deg 44 min E), southern Yilgarn Block, Western Australia, Australia, where it is intimately intergrown with black cesstibtantite, manganotantalite, antimonian microlite, rankamaite-like fibers, and montmorillonite, having formed by supergene weathering of a primary tantalum mineral (likely tantalite or Rankamaite). Combined MAC electron-microprobe analysis of polished particle mounts and CHN elemental microanalysis at 1000 degrees C in oxygen (Table 1, p. 574) yielded on the raw bulk sample Ta2O5 78.5, Nb2O5 6.6, Na2O 0.7, FeO 0.4, Sb2O3 0.7, CO2 2.8, H2O 5.9, sum 95.6 wt%; correcting the volatile-element analysis for ~28% admixed anhydrous cesstibtantite (determined from bulk Cs and Sb XRF contents) gave the normalized kimrobinsonite composition Ta2O5 78.5, Nb2O5 6.6, H2O 8.9, CO2 4.2, Na2O 0.7, Sb2O3 0.7, FeO 0.4, total 100.0 wt%, corresponding on the basis of 1 cation per unit cell to the empirical formula Ta0.82Nb0.11Na0.05Fe0.01Sb0.01(OH)2.27(CO3)0.22O1.02. 80-mm Guinier camera powder X-ray diffraction (Table 2, p. 575) indexed on a primitive cubic unit cell with a = 3.812(1) A, V = 55.39 A3, Z = 1, Dcalc = 6.865 g/cm3 (6.87 g/cm3 in abstract), ncalc = 2.23, and micro-indentation hardness VHN20 = 70(12) (Mohs ~2-2.5), interpreted as an A-site-vacant perovskite-like ABX3 framework (with B = Ta,Nb and X = OH,O,CO3). Distinct from cesstibtantite, sosedkoite, rankamaite, natrotantite, and elemental tantalum, niobium, or antimony; no criticality designation, microbial mechanism, or industrial recovery yield is asserted.

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Record source: data/records/kimrobinsonite.yaml