Wollastonite: Gemstones Information
Wollastonite is CaSiO3 and forms transparent to translucent tabular or long prismatic crystals of the monoclinic or triclinic system with hard-ness 4.5–5 and one direction of perfect cleavage. The colour is white, colourless or brown, red, yellow or pale green. The SG is 2.8–3.09 and the RI for the alpha, beta and gamma rays is 1.616–1.640, 1.628–1.650 and 1.631–1.653, biaxial negative with birefringence 0.148. Wollastonite occurs in thermally metamorphosed siliceous carbonates and in some alkalic igneous rocks and carbonatites. Some fibrous wollastonite may produce cat’s-eyes and a few crystals from Mt Saint Hilaire, Quebec, Canada, have been faceted. Large crystals have been reported from Belafa, Madagascar. Some texts report a compact ornamental variety from Isle Royale, Lake Superior, USA.