Magnesite: Gemstone Information
Magnesite is MgCO3; crystals are rare, the common occurrence being as translucent, sometimes transparent colourless, white, yellowish to brown or grey masses with an earthy or chalky appearance. The crystal system is trigonal; there is one direction of perfect cleavage and the hardness is 3.5–4.5 with SG 3.0–3.1. The RI for the ordinary and extraordinary rays is 1.710 and 1.509, uniaxial negative with birefringence 0.202, very easy to see in the occasional faceted specimen. Under SWUV blue green or white fluorescence may be seen with greenish phosphorescence.Magnesite occurs as a primary mineral in igneous or sedimentary rocks or may be formed by the metamorphism or alteration of serpentine and peridotite. Fine crystals come from Brumado, Bahia, Brazil.