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. Tremolite forms a series with 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, one of the two minerals of the gemstone , 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 and both pleural. Fibrous tremolite is sometimes found as a contaminant in vermiculite , chrysotile.