Tremolite

Tremolite, a member of the amphibole group of rock-forming minerals (see AMPHIBOLE). It is a calcium and magnesium metasilicate, CaMg 3 (SiO 3) 4, crystallizing in the monoclinic system with an angle of 55° 49' between the perfect prismatic cleavages. It occurs sometimes as distinct crystals, but more usually as long bladed and fibrous forms. The colour is white or grey, but when iron is present it is green, then forming a passage to actinolite. The hardness is 51 and the specific gravity 3. o. Tremolite is a characteristic mineral of crystalline limestones, especially dolomitic limestones, but also occurs as an alteration-product of olivine in basic igneous rocks. Typical specimens have long been known from the white crystalline dolomite of Campolongo in the St Gotthard region, Switzerland, near to which is the Tremola Valley, after which the mineral was named in 1796. Fine crystals are found in crystalline limestone at Gouverneur, Pierrepont and other places in New York, and at several localities in Sweden. (L. J. S.)