Fibroferrite - Encyclopedia
Class : Sulfates, chromates, molybdates
Subclass : Hydrated sulfates
Crystal system : Trigonal
Chemistry : Fe(SO4)(OH) 5H2O
Rarity : Rare to uncommon
Fibroferrite is a rare iron sulfate formed by alteration of iron sulfides, mainly in arid climates. It is a secondary mineral which is part of a procession to which other iron sulfates belong (copiapite, voltaite, jarosite, coquimbite, botryogen, etc...), resulting like it from precipitation from natural sulfuric acid formed by reaction of surface water with iron sulphides. By changing environmental conditions (temperature, pH, redox potential, etc...) these sulfates are easily hydrolyzed into ferric hydroxides (goethite or limonite). Fibroferrite is easily subject to dehydration at room temperature. Its name derives from the Latin fibra (fiber) and ferrum (iron) in allusion to its fibrous habit and its chemical composition. It essentially forms fibrous masses, sometimes botryoidal, and encrustations composed of white, yellowish to yellowish-green, sometimes green or light brown, acicular to bacillary crystals.
Main photo : Fibroferrite from Trenning graphite mine, Mühldorf, Austria © Christian Auer
Fibroferrite in the World
Twinning
No twins known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species.
Hardness : 2 to 2.5
Density : 1.84 to 2.1
Fracture : Fibrous
Streak : White
TP : Translucent
RI : 1.530 to 1.570
Birefringence : 0.038
Optical character : Uniaxial +
Pleochroism : Visible
Fluorescence : None
Solubility : Water
Magnetism : None
Radioactivity : None