Tremolite

Tremolite
Tremolite from the type locality in Switzerland
General
Category	Amphiboles
Formula (repeating unit)	☐Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2
Strunz classification	9.DE.10
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Unit cell	a = 9.84 Å, b = 18.02 Å c = 5.27 Å; β = 104.95°; Z = 2
Identification
Color	White, gray, lavender to pink, light green, light yellow
Crystal habit	Elongated prismatic, or flattened crystals; also as fibrous, granular or columnar aggregates
Twinning	Simple or multiple, common parallel to {100}; rarely parallel to {001}
Cleavage	Perfect on {110} at 56° and 124°; partings on {010} and {100}
Tenacity	Brittle
Mohs scale hardness	5 – 6
Luster	Vitreous and silky
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.99 – 3.03
Optical properties	Biaxial (-)
Refractive index	nα = 1.599 - 1.612 nβ = 1.613 - 1.626 nγ = 1.625 - 1.637
Birefringence	δ = 0.026
2V angle	Measured: 86° to 88°
Ultraviolet fluorescence	Short UV=yellow, Long UV=range pink
References

Tremolite is a member of the amphibole group of silicate minerals with composition: ☐Ca₂(Mg_5.0-4.5Fe²⁺_0.0-0.5)Si₈O₂₂(OH)₂. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and ferro-actinolite. Pure magnesium tremolite is creamy white, but the color grades to dark green with increasing iron content. It has a hardness on Mohs scale of 5 to 6. Nephrite, one of the two minerals of the gemstone jade, is a green variety of tremolite.

The fibrous form of tremolite is one of the six recognised types of asbestos. This material is toxic and inhaling the fibers can lead to asbestosis, lung cancer and both pleural and peritoneal mesothelioma. Fibrous tremolite is sometimes found as a contaminant in vermiculite, chrysotile (itself a type of asbestos) and talc.

Tremolite is an indicator of metamorphic grade since at high temperatures it converts to diopside.

Tremolite occurs as a result of contact metamorphism of calcium and magnesium rich siliceous sedimentary rocks and in greenschist facies metamorphic rocks derived from ultramafic or magnesium carbonate bearing rocks. Associated minerals include calcite, dolomite, grossular, wollastonite, talc, diopside, forsterite, cummingtonite, riebeckite and winchite.