Ferrosilite - Encyclopedia
Class : Silicates
Subclass : Inosilicates
Crystal system : Orthorhombic
Chemistry : FeSiO3
Rarity : Common
Ferrosilite belongs to the group of orthorhombic pyroxenes (orthopyroxenes). It forms a series with enstatite (magnesian) and hypersthene. It is a constituent of basic and ultrabasic rocks (especially gabbros and norites) as well as BIFs. It is also present but rarer in high grade metamorphic rocks (granulites and charnockites), contact deposits (hornfel), and volcanic rocks. Its name comes from its chemical composition : iron + silicon. Clear crystals are rare and only known in gabbroic pegmatites : they are then flattened prisms. Ferrosilite generally occurs in fibrous, lamellar, grainy or compact masses, greenish black to brownish black, sometimes dark green or dark brown. It changes into amphibole (uralitization). It is exceptionally used as a gem.
Main photo : Ferrosilite from Caspar quarry, Ettringen, Germany © Volker Betz
Ferrosilite in the World
Twinning
No twins known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species.
Hardness : 5 to 6
Density : 3.6 à 4
Fracture : Irregular
Streak : Gray-brown
TP : Translucent to transparent
RI : 1.71 to 1.788
Birefringence : 0.016 to 0.021
Optical character : Biaxial +
Pleochroism : Low
Fluorescence : None
Solubility : Hydrochloric acid
Magnetism : Paramagnetic
Radioactivity : None