Formula: Fe3+(SO4)(OH).5H2O
Hydrated sulphate containing hydroxyl, fibroferrite group
Specific gravity: 1.84 to 2.1
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)

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).


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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