Tremolite

Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2(Mg5.0-4.5Fe2+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.

Tremolite
General
CategoryInosilicates
Formula
(repeating unit)		Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2
Strunz classification9.DE.10
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Unit cella = 9.84 Å, b = 18.02 Å
c = 5.27 Å; β = 104.95°; Z = 2
Identification
ColorWhite, gray, lavender to pink, light green, light yellow
Crystal habitElongated prismatic, or flattened crystals; also as fibrous, granular or columnar aggregates
TwinningSimple or multiple, common parallel to {100}; rarely parallel to {001}
CleavagePerfect on {110} at 56° and 124°; partings on {010} and {100}
TenacityBrittle
Mohs scale hardness5 – 6
LusterVitreous and silky
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.99 – 3.03
Optical propertiesBiaxial (-)
Refractive indexnα = 1.599 - 1.612 nβ = 1.613 - 1.626 nγ = 1.625 - 1.637
Birefringenceδ = 0.026
2V angleMeasured: 86° to 88°
Ultraviolet fluorescenceShort UV=yellow, Long UV=range pink
References[1][2][3][4]

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
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

One of the six recognized types of asbestos. Approximately 40,200 tons of tremolite asbestos is mined annually in India.[5] It is otherwise found as a contaminant.

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

References
  1. Mindat.org
  2. Handbook of Mineralogy
  3. Webmineral data
  4. IMA Master List
  5. Furquan, Ahmad Ansari. "Asbestos: Foe or Friend?". Indmedica Cyber Lectures. Indmedica. Retrieved 2 January 2012.
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