Halotrichite
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Halotrichite, also known as feather alum, is a highly hydrated sulfate of aluminium and iron. Its chemical formula is FeAl24·22H2O. It forms fibrous monoclinic crystals. The crystals are water-soluble
A sample of halotrichite
Halotrichite from California
Halotrichite from the abandoned Golden Queen mine on Soledad Mountain south of Mojave, California
Copiapite
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Copiapite is a hydrated iron sulfate mineral with formula: Fe2+Fe3+462·20. Copiapite can also refer to a mineral group, the copiapite group.
Copiapite from the Bolesław Mine, Kłodzko District, Lower Silesia, Poland
Lustrous, micaceous crystals of copiapite to 8 mm on matrix from the Alcaparrosa Mine, El Loa Province, Antofagasta Region, Chile (sample size: 11.9 × 7.4 × 4.0 cm)