Tremolite

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Tremolite
Tremolite Campolungo.jpg
Tremolite from the type locality in Switzerland
General
Category Amphiboles
Formula
(repeating unit)
Ca2Mg5Si8O22(OH)2
Strunz classification 9.DE.10
Crystal symmetry Monoclinic 2/m prismatic
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
Crystal system Monoclinic
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 [1][2][3]

Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2Mg5Si8O22(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.

Occurrence[edit]

Tremolite from the Aure Valley, French Pyrenees (size: 8.2 x 6.7 cm)

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.[2]

Tremolite was first described in 1789 for an occurrence in Campolungo, Piumogna Valley, Leventina, Ticino (Tessin), Switzerland.[1]

Fibrous tremolite[edit]

One of the six recognised types of asbestos. Approximately 36,500 tonnes of tremolite asbestos are mined annually in India.[4] It is otherwise only found as a contaminant.

See also[edit]

  • Libby, Montana – location of asbestos-related ailments caused by tremolite

References[edit]

  1. ^ a b Mindat.org
  2. ^ a b Handbook of Mineralogy
  3. ^ Webmineral data
  4. ^ Furquan, Ahmad Ansari. "Asbestos: Foe or Friend?". Indmedica Cyber Lectures. Indmedica. Retrieved 2 January 2012.