Uranoan thorite in lithophysal rhyolite - Topaz Mountain, Utah, U.S.A.
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Abstract
Uranoan thorite crystals have been found occurring as a sparse constituent in lithophysae in 6.1 to 6.8 Ma alkali rhyolite flows at Thomas Mountain, Utah, USA. The crystals are associated with sandidine, quartz, topaz, hematite, magnetite, and calcite; they are leek to dark grass green, transparent, well-formed, euhedral prisms, showing development of forms {100}, {101}, and {111}. The mineral is both optically isotropic, with a refractive index of 1.86(1), and X-ray amorphous, indicating its metamict state. Electron microprobe analysis yields: SiO2 17.3, ThO2 56.8, UO2 25.4, total 99.5%, and a structural formula of (Th0.72U0.31)Σ1.03Si0.97O4.
This appears to be the first reported occurrence of thorite in volcanic rocks of rhyolitic composition, and may account for part or all of the Th reported in alkali rhyolites and so-called ‘topaz-rhyolites’ of the western USA.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Uranoan thorite in lithophysal rhyolite - Topaz Mountain, Utah, U.S.A. |
| Series title | Mineralogical Magazine |
| DOI | 10.1180/minmag.1985.049.354.13 |
| Volume | 49 |
| Issue | 354 |
| Year Published | 1985 |
| Language | English |
| Publisher | Cambridge University Press |
| Description | 3 p. |
| First page | 729 |
| Last page | 731 |
| Country | United States |
| State | Utah |
| Other Geospatial | Topaz Mountain |
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