Enstatite: Gemstones Information
Enstatite is Mg2Si2O6, dimorphous with clinoenstatite and forms a series with ferrosilite in the pyroxene mineral group. Use of the names hypersthene and bronzite has been discontinued. Crystals of the orthorhombic system are prismatic with two directions of good cleavage, hardness 5–6,SG 3.20–3.30. Both lamellar and simple twinning is common. The colour ranges from colourless through yellow, green to brown and there is a characteristic pink to green pleochroism. A strong absorption line at 506 nm is also characteristic. The RI for the alpha, beta and gamma raysis 1.649–1.667, 1.653–1.671 and 1.657–1.680, biaxial positive with birefringence 0.010. Star stones with 4-rays are fairly common.Enstatite occurs in pyroxenites, peridotites and dunites and in ultramafic inclusions in alkalic olivine basalts and kimberlite and in several other contexts. A rare transparent emerald-green variety occurs with diamond at Kimberley, South Africa and different colours occur in Sri Lankan alluvial deposits. A yellowish green variety has been reported from Mairimba Hill, Kenya.