Sodian potassian hydroxonian meta-autunite, (Na0.56K0.29(H3O)0.16) · UO2 · PO4 · 3.25H2O, is a novel member of the meta-autunite group. It occurs in a playa 105 km NNE of Kalgoorlie, Western Australia as void and fracture infillings in near-surface gypsiferous muds. Mineral aggregates are bright greenish yellow with a strong yellow fluorescence under UV light and consist of micaceous crystallites usually 20–50 μm in diameter. The mineral has a R.I. of 1.575–1.580 and is probably uniaxial, optically negative. Reversible dehydration occurs readily on heating or under vacuum; dehydration is complete above 300°C but remains reversible even after partial melting has occurred on heating to 1200°C. Principal X-ray diffraction lines are d = 4.94(110), 3.49(200), 2.47(113) and 220), 1.559(420). By the Guinier powder technique, these lines have intensities 75, 100, 75 and 50 respectively. These correspond to a meta-autunite I structure with tetragonal pseudo-cell dimension a′ = 6.971 Å and c′ = 8.545Å. Heating did not produce a phase equivalent to the meta-autunite II structure. The sodian potassian hydroxonian meta-autunite is the first reported occurrence of an intermediate member of a predicted solid solution series with potassium, sodium and hydroxonium end members. It differs in origin from other naturally-occurring autunite and meta-autunite minerals in being a direct precipitate from groundwater, rather than an alteration product.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.