Paulscherrerite

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What is Paulscherrerite?

Paulscherrerite, UO2(OH)2, is a newly named mineral of the schoepite subgroup of hexavalent uranium hydrate/hydroxides. It is monoclinic, but no space group has been determined because no single-crystal study has been done. Paulscherrerite occurs as a canary yellow microcrystalline powdery product with a length of ~500 nm. It forms by the weathering and ultimate pseudomorphism of uranium-lead bearing minerals such as metaschoepite. The type locality for paulscherrerite is the Number 2 Workings, Radium Ridge near Mount Painter, North Flinders Ranges, South Australia, an area where radiogenic heat has driven hydrothermal activity for millions of years. It is named for Swiss physicist Paul Scherrer, co-inventor of the Debye-Scherrer X-ray powder diffraction camera. Study of paulscherrerite and related minerals is important for understanding the mobility of uranium around mining sites, as well as designing successful strategies for the storage of nuclear weapons and the containment of nuclear waste.

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Key Characteristics

Characteristics of Paulscherrerite

Paulscherrerite occurs as a microcrystalline powdery product with a maximum length of ~500 nm. It forms by the weathering and ultimate pseudomorphism of uranium-lead bearing minerals such as metaschoepite. Paulscherrerite is canary yellow, with a yellow streak, and no fluorescence. The Mohs hardness cannot be measured due to the powdery nature of the mineral, and no cleavage or fracture is observable. The calculated density is 6.66 g/cm3 for the ideal formula UO2(OH)2. No optical properties have been recorded. See Table 1 for a list of the physical properties of paulscherrerite.

Composition of Paulscherrerite

The empirical formula for paulscherrerite is UO3 · 1.02H2O. The formulas for the rest of the schoepite group are: schoepite (UO2)8O2(OH)12 · 12H2O and metaschoepite UO3 · 1-2H2O. Electron microprobe 20 point analyses showed that it is an almost pure uranyl oxide-hydroxide/hydrate, with less than ~1 wt% of minor elements such as Al, Ba, and Pb. The simplified structural formula is UO2(OH)2, which requires the presence of water: UO3 93.96, H2O 6.04, Total 100.00 wt%. Table 1 shows an analysis of the chemical composition. Because paulscherrerite always exists in powder form, mixed with substantial amounts of metaschoepite, thermogravimetric analysis (TGA) is the best method of water measurement.

Quick Facts

Physical Properties

Color
canary yellow
Density
6.66 g/cm³
Streak
canary yellow

Chemical Properties

Chemical Formula
UO2(OH)2
Elements
H, O, U
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