Increasing iron content will raise the specific gravity, index of refraction and darken the color. A variety of tremolite is composed of microscopically fibrous crystals called asbestos. Other minerals also form asbestos such as serpentine and the other minerals of the series mentioned above. Serpentine asbestos is more widely used and of a better grade in general. Although asbestos has been shown to cause cancer in humans when inhaled in high enough concentrations, it still has many valuable applications.
Asbestos is used for fire retardant materials and brake shoes and pads.
Its prior use as insulation has been all but eliminated due to health concerns. A variety of actinolite, nephrite , is one of the two minerals called jade . The other jade mineral is jadeite . Although nephrite is considered to be actinolite, the lighter shades of nephrite probably contain significant amounts of tremolite. The tremolite fibers form a felted mass that has all the appearances and feel of a piece of cloth.