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UM1990-23-O:Al
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Formula:
θ-Al2O3
Colour:
yellowish
Polymorph of:
Co-described with UM1990-24-O:Al, which was later shown to be the σ-Al2O3 phase.
Also associated with corundum.
The association is found as polycrystalline spherules, ca. 0.1 mm in diameter; they stand for 2-3% of a heavy fraction of minerals separated from loam and sandy loam (Upper Pleistocene to Holocene age) in different locations. of Yakutiya, USSR. The aluminous spherules are confined to layers, connected with formation of cryogenic soils. These metastable alumina polymorphs are though to be formed due to dehydration of colloidal aluminum hydroxides at subfreezing temperatures in the presence of saline pore solutions. They come from natural exposures within an uninhabitated area.
Paglia (2004) reports the following calcination pathway: gibbsite → böhmite → γ-Al2O3 (Unnamed (gamma-alumina)) → δ-Al2O3 (synthetic equivalent of deltalumite) → θ-Al2O3 (synthetic equivalent of UM1990-23-O:Al) → α-Al2O3 (corundum).
Also associated with corundum.
The association is found as polycrystalline spherules, ca. 0.1 mm in diameter; they stand for 2-3% of a heavy fraction of minerals separated from loam and sandy loam (Upper Pleistocene to Holocene age) in different locations. of Yakutiya, USSR. The aluminous spherules are confined to layers, connected with formation of cryogenic soils. These metastable alumina polymorphs are though to be formed due to dehydration of colloidal aluminum hydroxides at subfreezing temperatures in the presence of saline pore solutions. They come from natural exposures within an uninhabitated area.
Paglia (2004) reports the following calcination pathway: gibbsite → böhmite → γ-Al2O3 (Unnamed (gamma-alumina)) → δ-Al2O3 (synthetic equivalent of deltalumite) → θ-Al2O3 (synthetic equivalent of UM1990-23-O:Al) → α-Al2O3 (corundum).
Unique Identifiers
Mindat ID:
51811
Long-form identifier:
mindat:1:1:51811:6
Similar Names
| UM1990-24-O:Al | σ-Al2O3 | |
| UM1995-15-O:Al | χ-Al2O3 | |
| UM1996-16-O:Al | η-Al2O3 |
Physical Properties of UM1990-23-O:Al
Colour:
Yellowish
Chemistry of UM1990-23-O:Al
Mindat Formula:
θ-Al2O3
Elements listed:
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 2.88 Å | (40) |
| 2.71 Å | (60) |
| 2.42 Å | (40) |
| 2.28 Å | (30) |
| 2.01 Å | (40) |
| 1.537 Å | (30) |
| 1.386 Å | (100) |
Comments:
coincides with PDF 4-875 pattern
Other Information
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for UM1990-23-O:Al
mindat.org URL:
https://www.mindat.org/min-51811.html
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References for UM1990-23-O:Al
Reference List:
Localities for UM1990-23-O:Al
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
Struck out - Mineral was erroneously reported from this locality.
Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).
All localities listed without proper references should be considered as questionable.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Russia | |
| Siegert et al. (1990) +1 other reference |
