Grunerite

Grunerite
Sprays of small, prismatic grunerite crystals on matrix, field of view 5mm, from Marquette Co., Michigan, US
General
Category	Inosilicate
Formula (repeating unit)	Fe7Si8O22(OH)2
IMA symbol	Gru
Strunz classification	9.DE.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Identification
Formula mass	1,001.61 g/mol
Color	Ashen, brown, brownish green, dark gray
Crystal habit	Columnar, acicular
Mohs scale hardness	5–6
Luster	Vitreous
Streak	Colorless
Diaphaneity	Translucent to opaque
Specific gravity	3.45
Density	3.4–3.5
Ultraviolet fluorescence	Non-fluorescent
Other characteristics	Not radioactive
References

Grunerite is a mineral of the amphibole group of minerals with formula Fe₇Si₈O₂₂(OH)₂. It is the iron endmember of the grunerite-cummingtonite series. It forms as fibrous, columnar or massive aggregates of crystals. The crystals are monoclinic prismatic. The luster is glassy to pearly with colors ranging from green, brown to dark grey. The Mohs hardness is 5 to 6 and the specific gravity is 3.4 to 3.5.

It was discovered in 1853 and named after Emmanuel-Louis Gruner (1809–1883), the Swiss-French chemist who first analysed it.

Amosite (fibrous grunerite)

Scanning electron microscope image of asbestos fibres (grunerite var. amosite)

Amosite is a rare asbestiform variety of grunerite that was mined as asbestos predominantly in the eastern part of the Transvaal Province of South Africa. The origin of the name is Amosa, the acronym for the mining company "Asbestos Mines of South Africa". In industry Amosite is referred to as "brown asbestos".