Grunerite is a mineral of the

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

group of minerals with formula Fe₇ Si₈ O₂₂( OH)₂. It is the iron endmember of the grunerite-

cummingtonite Cummingtonite ( ) is a metamorphic amphibole with the chemical composition , magnesium iron silicate hydroxide. Monoclinic cummingtonite is compositionally similar and polymorphic with orthorhombic anthophyllite, which is a much more common fo ...

series. It forms as fibrous, columnar or massive aggregates of crystals. The crystals are

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic ...

prismatic. The luster is glassy to pearly with colors ranging from green, brown to dark grey. The

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by ...

is 5 to 6 and the

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...

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)

Amosite is a rare asbestiform variety of grunerite that was mined as

asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...

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".

References

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Inosilicates Iron(II) minerals Asbestos Monoclinic minerals Minerals in space group 12 {{silicate-mineral-stub