Halotrichite
(repeating unit)FeAl2(SO4)4·22H2O IMA symbol Hth[1] Strunz classification 7.CB.85 Crystal system Monoclinic Crystal class Prismatic (2m)
(same H-M symbol) Space group P21/c Unit cell a = 20.51, b = 24.29
c = 6.18 [Å]; β = 100.99°; Z = 4 Identification Color Colorless to white, yellowish, greenish Crystal habit Acicular to asbestiform clusters, incrustations and efflorescences Cleavage Poor on {010} Fracture Conchoidal Tenacity Brittle Mohs scale hardness 1.5–2 Luster Vitreous Diaphaneity Transparent, translucent Specific gravity 1.89 Optical properties Biaxial (−) Refractive index nα = 1.480 nβ = 1.486 nγ = 1.490 Birefringence δ = 0.010 2V angle Measured: 35° Solubility Soluble in water Other characteristics Astringent taste References [2][3][4]
(same H-M symbol)
c = 6.18 [Å]; β = 100.99°; Z = 4
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.[4]
- Gallery
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Halotrichite from California -
Halotrichite from the abandoned Golden Queen mine on Soledad Mountain south of Mojave, California
References
- Saint-Hilaire
- Mineral Atlas
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