Datolite: Gemstones Information
Datolite is CaBSiO4(OH) and forms characteristic short prismatic mono clinic crystals. Transparent colourless crystals have been faceted and other pale colours turn up from time to time. The hardness is 5–5.5 the SG 2.96–3.00 and the RI for the alpha, beta and gamma rays is 1.622–1.626,1.649–1.654, 1.666–1.670 biaxial negative with birefringence 0.044–0.047.Some specimens may fluoresce blue under SWUV, perhaps from europium impurities. Datolite occurs as a secondary mineral in mafic igneous rocks,in geodes in tuffs or skarns in limestones, in serpentinites and hornblende schists and in some ore veins. Gem-quality datolite has come usually from the Lane quarry, Westfield, Mass., from other workings in the eastern US (pale green specimens from Paterson, New Jersey) or from Charcas,San Luis Potosi, Mexico. Some datolite from Michigan, USA, contains included copper. Datolite is also found in the Habachtal, Austria.