Fuchsite

Fuchsite
Verdite, a microcrystalline metamorphic rock, is composed mostly of green fuchsite. This specimen (6.5 cm across at its base), of Archean age, is from Barberton, Mpumalanga, South Africa
General
Category	Silicate mineral
Crystal system	Monoclinic
Identification
Color	Light to medium green
Crystal habit	Curved aggregates
Cleavage	Perfect basal
Fracture	Uneven
Mohs scale hardness	2.5
Luster	Vitreous to pearly
Streak	White
Diaphaneity	Transparent to opaque
Specific gravity	2.8–2.9
Optical properties	Biaxial (–)
Refractive index	1.552–1.615
Birefringence	0.036
Dispersion	weak
References

Fuchsite, also known as chrome mica, is a chromium (Cr)-rich variety of the mineral muscovite, belonging to the mica group of phyllosilicate minerals, with the chemical formula K(Al,Cr)₂(AlSi₃O₁₀)(OH)₂.

Trivalent chromium replaces one of the aluminium (Al) atoms in the general muscovite formula producing the apple green hue distinctive of fuchsite. It is often found in minute micaceous aggregates (with individual plates barely visible), as a major component of chromium rich phyllitic or schistose metamorphic rocks of the greenschist facies.

Verdite is a type of metamorphic rock made mostly of an impure, often multicolored, variety of fuchsite. It is used for ornamental carvings.

Fuchsite is named after the German chemist and mineralogist Johann Nepomuk von Fuchs.

Properties

Fuchsite crystallizes in the monoclinic crystal system. Common colour of the mineral is pale green to emerald green depending on the amount of Cr substitution. The micaceous crystals are flexible and slightly sectile with a hardness of 2-2.5 on the Mohs scale. Fuchsite fluoresces lime green under long wave UV light. Fuchsite's radioactivity due to its potassium (K) content is barely detectable.

External links

• webmineral.com - Muscovite/Fuchsite