Bassanite

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Bassanite
Bassanite-192766.jpg
Bassanite (3.0 by 2.6 cm white mass with some gypsum crystals)
General
CategorySulfate mineral
Formula
(repeating unit)
CaSO4·0.5(H2O)
Strunz classification7.CD.45
Crystal systemMonoclinic
Space groupSpheroidal (2)
(same H-M symbol)
Unit cella = 12.0317 Å,
b = 6.9269 Å,
c = 12.6712 Å, β = 90.27°; Z = 12
Identification
ColorWhite
Crystal habitMicroscopic acicular crystals in parallel aggregates, pseudohexagonal
TwinningTwin plane {101}
LusterEarthy
StreakWhite
DiaphaneitySemitransparent
Specific gravity2.69–2.76
Optical propertiesBiaxial (+)
Refractive indexnα = 1.550–1.559, nβ = 1.560, nγ = 1.577–1.584
2V angle10-15°
Alters toDehydrates on heating to anhydrite
References[1][2][3]

Bassanite is a calcium sulfate mineral with formula CaSO4·0.5(H2O) or 2CaSO4·H2O. In other words it has half a water per CaSO4 unit hence its synonym hemihydrate.

Bassanite was first described in 1910 for an occurrence on Mount Vesuvius. It was named for Italian paleontologist Francesco Bassani (1853–1916).[1]

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.[2]

References[edit]