White radial-acicular bassanite crystals from Kimba, Eyre Peninsula, South Australia
General
Category
Sulfate mineral
Formula (repeating unit)
CaSO4·1/2H2O
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 calcium sulfate mineral with formula CaSO4·1/2H2O or 2CaSO4·H2O. In other words it has half a water molecule per CaSO4 unit, hence its synonym calcium sulfate hemihydrate.
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]
^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.
Bassanite is a calcium sulfate mineral with formula CaSO4·1/2H2O or 2CaSO4·H2O. In other words it has half a water molecule per CaSO4 unit, hence its...
air it loses water and converts first to calcium sulfate hemihydrate (bassanite, often simply called "plaster") and, if heated further, to anhydrous calcium...
CaSO 4·2H 2O (gypsum and selenite (mineral)): dihydrate. CaSO 4·1/2H 2O (bassanite): hemihydrate, also known as plaster of Paris. Specific hemihydrates are...
was merely a dense variety of basalt. Basanite (not to be confused with bassanite), Lydian stone, and radiolarite (a.k.a. lydite or flinty slate) are terms...
sulfate hemihydrate. The natural form of the compound is the mineral bassanite. The name "plaster of Paris" was given because it was originally made...
who he married in 1880. A mineral from Vesuvius was named after him as bassanite in 1906. He died at Capri. Alfano, Giov. Batt. (1916). "Commemorazione...
the grinding process causes gypsum (CaSO4.2H2O) to lose water, forming bassanite (CaSO4.0.2-0.7H2O) or γ-anhydrite (CaSO4.~0.05H2O). The latter minerals...
mineral phase of hydrated cement paste), the calcium sulfates (gypsum, bassanite, and anhydrite) and lanthanoid sulfates whose dissolution reactions are...
Meridiani Planum, and Arabia. Examples of Martian sulphates include gypsum, bassanite, kieserite, jarosite, and alunite. Polyhydrated sulphates: Absorption...
sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum. Salts, such as halite, bischofite...
of Badwater. Possibly also as dry-period efflorescence on floodplains. Bassanite 2CaSO4·H2O As layer capping massive gypsum along west side of Badwater...
sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum. Salts, such as halite, bischofite...
minerals identified via meteorites include epsomite, bloedite, gypsum/bassanite, and jarosite. As the name implies, carbonaceous chondrites formed with...
icarus.2009.07.014. Wray; et al. (2010). "Identification of the Ca-sulfate bassanite in Mawrth Vallis, Mars". Icarus. 209 (2): 416–421. Bibcode:2010Icar..209...
use. The most common mineral deposited at Salar Ignorado is gypsum, but bassanite, epsomite, halite, jarosite and thenardite also occur. The gypsum crystals...
central lava dome and iron-bearing deposits has generated alunite, anatase, bassanite, chlorite, copper veinlets, gypsum, illite, jarosite, kaolinite, labradorite...
icarus.2009.07.014. Wray; et al. (2010). "Identification of the Ca-sulfate bassanite in Mawrth Vallis, Mars". Icarus. 209 (2): 416–421. Bibcode:2010Icar..209...
icarus.2009.07.014. Wray; et al. (2010). "Identification of the Ca-sulfate bassanite in Mawrth Vallis, Mars". Icarus. 209 (2): 416–421. Bibcode:2010Icar..209...
sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum. Salts, such as halite, bischofite...
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