Smithsonite: Gemstones Information
Smithsonite is ZnCO3 and in the trigonal system forms typically reniform or botryoidal translucent masses; fine transparent to translucent crystals may be rhombohedral or scalenohedral with one direction of nearly perfect cleavage. The colour is pale to deep yellow, sometimes pink, more commonly blue-green. The hardness is 4–4.5 and the SG 4.43. The RI for the ordinary and extraordinary rays is 1.842–1.850 and 1.619–1.623, uniaxial negative with birefringence 0.227. Smithsonite occurs as a secondary mineral in the oxidized zone of zinc-bearing deposits. Notably fine, near-transparent crystals are found at the Kelly mine, Magdalena, Socorro County, new Mexico, USA; pink smithsonite is found in some Mexican deposits and transparent yellow crystals occur at Tsumeb, Namibia. The classical slags at Lavrion, Greece, provideattractive translucent material. A beautiful translucent green smithsonite,which could be mistaken for one of the jade minerals, occasionally appears on the specialist collectors’ market.