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Formula: Fe3+(SO4)(OH).5H2O
Hydrated sulphate, fibroferrite group
Crystal System: Trigonal
Specific gravity: 1.84 to 2.1 measured, 1.996
Hardness: 2 to 2½
Streak: White
Colour: Light yellow, golden yellow, nearly white, greenish grey, yellowish green, light green, colourless to faint yellow in
transmitted light
Solubility: Decomposed by water, rendering an acidic solution and a brown precipitate of hydrated iron oxide (Mindat)
Environments
Hydrothermal environments
Volcanic sublimates rare
Fibroferrite is an uncommon dehydration product of melanterite in oxidised
portions of rocks and sediments containing iron sulphide, most stable in arid regions. It also occurs rarely as a volcanic sublimate.
Associated minerals include melanterite,
amarantite, hohmannite,
krausite, coquimbite,
parabutlerite, butlerite,
copiapite, epsomite,
gypsum and pyrite
(HOM).
Localities
The type locality is Tierra Amarilla, Copiapó Province, Atacama, Chile.
At Borate, Pacific mine, Calico, Calico District, Calico Mts, San Bernardino county, California, USA, fibroferrite is
associated with krausite, coquimbite and
other sulphates
(Dana).
At the Island Mountain Mine, Moose Peak, Island Mountain, Coastal Range, Trinity county, California, USA,
fibroferrite occurs
in the pyrrhotite deposit
(Dana).
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