tremolite

Tremolite is a calcium-magnesium amphibole mineral that belongs to the amphibole group. Its ideal chemical formula is Ca2(Mg5Si8O22)(OH)2, with iron able to substitute for magnesium to form ferro-tremolite and related members of the tremolite-actinolite series. It is typically colorless to white in its pure form, but iron-bearing varieties can appear pale green, gray, or brown.

Tremolite forms during regional or contact metamorphism of dolomitic limestone and calc-silicate rocks. It occurs in metamorphic environments such as marble, schist, and gneiss, and commonly associates with minerals like calcite, diopside, talc, chlorite, and wollastonite. It is often found in skarns at carbonate rock contact zones.

In terms of structure and appearance, tremolite crystallizes in the monoclinic system and usually forms prismatic crystals, though it can appear as fibrous aggregates, especially in altered rocks. Cleavage is two-directional, with angles near 56 and 124 degrees. Its hardness is about 5–6 on the Mohs scale, and its specific gravity ranges roughly from 3.0 to 3.4.

Health and usage notes: tremolite in fibrous form is a recognized asbestos mineral (tremolite asbestos), which poses serious health risks such as asbestosis, lung cancer, and mesothelioma. Because of these hazards, tremolite is not used as a major ore or gemstone, and fibrous forms are subject to strict regulation and avoidance in consumer products.