Diopside: Gemstones Information
Diopside is a member of the pyroxene group of silicates and provides transparent mostly green to brown monoclinic prismatic crystals with nearly square cross-section and twinning common. There is a distinct cleavage in one direction and the hardness is 5.5–6.5. The SG is in therange 3.22–3.38, increasing with increasing iron content; the composition is CaMgSi2O6; diopside forms two series, one with hedenbergite and one with johanssenite. The RI for the alpha, beta and gamma rays is 1.664,1.672 and 1.694 with a mean birefringence of 0.026, biaxial positive.Pleochroism for the important chrome green material is yellow and green.While gem diopside is most commonly green, this colour may result from either chromium (chrome diopside) or iron impurities.The absorption spectrum of chrome green diopside shows a doublet at 690 nm with other absorptions at 670, 655, 635, 508, 505 and 490 nm; paler green specimens show absorptions at 505, 493 and 446 nm.A bluish, sometimes a fine violet variety of diopside has been called violane and comes from St Marcel, Val d’Aosta, Italy.
Star stones with four notably sharp rays come from Myanmar; the rays are alternately strong and weak The background may be near-black. Four-rayed star diopside has been reported from southern India, some specimens responding to a magnet; magnetite inclusions may be responsible. Chatoyant diopside is also found. Some diopside may luminesce but the iron content prevents significant response in most cases. Under LWUV some green specimens show green, do not respond to SW and show a dull mustard-yellow glow under X-rays. Fine emerald-green chrome diopside is found in association with diamond from the Kimberley mines and in the Mogok Stone Tract of Myanmar. Fine green diopside is also found at Outukumpu, Finland and at De Kalb, New York, USA. Diopside of a more sober green is found in the Sri Lankan gem gravels and in the state of Minas Gerais, Brazil.Smoky yellow or brownish diopside is found at locations in Ontario and Quebec, Canada. A fine green mineral at one time reported from the Northern Areas of Pakistan as diopside is pargasite (q.v.).