Bassanite
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| Bassanite | |
|---|---|
| Lua error in package.lua at line 80: module 'Module:InfoboxImage/data' not found. White radial-acicular bassanite crystals from Kimba, Eyre Peninsula, South Australia | |
| General | |
| Category | Sulfate mineral |
| Formula | CaSO4·Page Template:Sfrac/styles.css has no content.1/2H2O |
| IMA symbol | Bss[1] |
| Strunz classification | 7.CD.45 |
| Crystal system | Monoclinic |
| Space group | C2 (No. 5) |
| Unit cell | a = 12.0317 Å, b = 6.9269 Å, c = 12.6712 Å, β = 90.27°; Z = 12 |
| Identification | |
| Color | White |
| Crystal habit | Microscopic acicular crystals in parallel aggregates, pseudohexagonal |
| Twinning | Twin plane {101} |
| Luster | Earthy |
| Streak | White |
| Diaphaneity | Semitransparent |
| Specific gravity | 2.69–2.76 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.550–1.559, nβ = 1.560, nγ = 1.577–1.584 |
| 2V angle | 10–15° |
| Alters to | Dehydrates on heating to anhydrite |
| References | [2][3][4] |
Bassanite is a sulfate mineral composed of calcium sulfate hemihydrate, with the chemical formula Page Module:Chem2/styles.css has no content.CaSO4·0.5H2O or Page Module:Chem2/styles.css has no content.2CaSO4·H2O. It has half a water molecule per CaSO4 unit.
Bassanite was first described in 1910 for an occurrence on Mount Vesuvius. It was named for Italian paleontologist Francesco Bassani (1853–1916).[2]
At Vesuvius it occurs as alterations from gypsum within leucite tephrite and as fumarole deposits. It occurs in dry lake beds in California and Australia. It also occurs interlayered with gypsum in caves.[3]
H. Schmidt and coinvestigators reported in 2011 that under dry conditions, the structure is monoclinic with space group C2, but at 75% humidity, the structure is trigonal with space group P3221. This reflects the incorporation of additional water of hydration, such that the trigonal form has the formula CaSO4·0.625H2O.[5]
References
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- ^ Page Module:Citation/CS1/styles.css has no content.Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ a b Bassanite on Mindat.org
- ^ a b Bassanite in the Handbook of Mineralogy
- ^ Bassanite data on Webmineral
- ^ Page Module:Citation/CS1/styles.css has no content.Schmidt, Horst; Paschke, Iris; Freyer, Daniela; Voigt, Wolfgang (1 December 2011). "Water channel structure of bassanite at high air humidity: crystal structure of CaSO 4 ·0.625H 2 O". Acta Crystallographica Section B: Structural Science. 67 (6): 467–475. doi:10.1107/S0108768111041759. PMID 22101536.
