a hard, white to dark-gray, monoclinic amphibole, CaMgSiO(OH), that is closely related to actinolite and found in either fibrous or crystalline form; hydrous calcium magnesium silicate
See tremolite in American Heritage Dictionary 4
(trĕmˈə-lītˌ)
noun
A white to dark gray amphibole mineral, Ca2Mg5Si8O22(OH)2, typically occurring in aggregates and used as a substitute for asbestos and in paints and ceramics.