Tremolite: Ca2Mg5Si8O22(OH)2 - Ca2Mg4.5Fe2+ 0.5Si8O22(OH)2
Sources: Tremolite is named for the locality, Val Tremela, in Italy.
Tremolite is part of a complete solid solution series from Tremolite to Ferroactinolite. All members differ by their relative amounts of Magnesium and Iron. Tremolite is at one end of the scale with a higher Mg to Iron ratio. When the total atomic Fe content to total Fe + Mg, exceeds 10% the species is no longer called Tremolite and is now Actinolite. As the iron content increases to > 50% the mineral is now classified as Ferroactinolite. In this solid solution series only Tremolite and Actinolite are regulated.
Tremolite is monoclinic and can exhibit inclined extinction by PLM. Tremolite's extinction angle may be as high as 15-20º. By PLM Tremolite is non-pleochroic. Tremolite is colorless. The refractive index typically varies from 1.60 to 1.65, with moderate birefringence. Random orientation SAED of Tremolite shows a layerline spacing of 5.3 Å with twinning being uncommon. Tremolite is a member of the amphibole double chain silicate group.
Uncommon in building materials except as a contaminant, contaminant in talc and some vermiculites, present in some soils as is the case in California.