This page uses content from Wikipedia and is licensed under CC BY-SA.

Halotrichite

Halotrichite
Mineraly.sk - halotrichit.jpg
A sample of Halotrichite
General
CategorySulfate minerals
Formula
(repeating unit)
FeAl2(SO4)4·22H2O
Strunz classification7.CB.85
Crystal systemMonoclinic
Crystal classPrismatic (2m)
(same H-M symbol)
Space groupP21/c
Unit cella = 20.51, b = 24.29
c = 6.18 [Å]; β = 100.99°; Z = 4
Identification
ColorColorless to white, yellowish, greenish
Crystal habitAcicular to asbestiform clusters, incrustations and efflorescences
CleavagePoor on {010}
FractureConchoidal
TenacityBrittle
Mohs scale hardness1.5 - 2
LusterVitreous
DiaphaneityTransparent, translucent
Specific gravity1.89
Optical propertiesBiaxial (-)
Refractive indexnα = 1.480 nβ = 1.486 nγ = 1.490
Birefringenceδ = 0.010
2V angleMeasured: 35°
SolubilitySoluble in water
Other characteristicsAstringent taste
References[1][2][3]

Halotrichite, also known as feather alum, is a highly hydrated sulfate of aluminium and iron. Its chemical formula is FeAl2(SO4)4·22H2O. It forms fibrous monoclinic crystals. The crystals are water-soluble.

It is formed by the weathering and decomposition of pyrite commonly near or in volcanic vents. The locations of natural occurrences include: the Atacama Desert, Chile; Dresden in Saxony, Germany; San Juan County, Utah; Iceland and Mont Saint-Hilaire, Canada.

The name is from Latin: halotrichum for salt hair which accurately describes the precipitate/evaporite mineral.[3]

Gallery

References