Tremolite is a member of the amphibole group of silicate minerals with composition Ca<sub>2</sub>(Mg<sub>5.0-4.5</sub>Fe<sup>2+</sup><sub>0.0-0.5</sub>)Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>. Tremolite forms by metamorphism of sediments rich in dolomite and quartz, and occurs in two distinct forms, crystals and fibers. 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 known as the gemstone jade, is a green crystalline variety of tremolite.
The fibrous form of tremolite is one of the six recognised types of asbestos. Inhaling asbestiform tremolite can lead to asbestosis, lung cancer and both pleural and malignant mesothelioma. Fibrous tremolite is sometimes found as a contaminant in vermiculite, chrysotile (itself a type of asbestos), and talc.
Occurrence
thumb|left|Tremolite from the Aure Valley, French Pyrenees (size: 8.2 × 6.7 cm)
thumb|left|Crystalline tremolite
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. It is otherwise found as a contaminant.
See also
- Libby, Montana – location of asbestos-related ailments caused by tremolite
References
- Mineral may unlock secrets of Venus's ancient oceans, New Scientist, 10 October 2007