What is Sphalerite?
Sphalerite is zinc sulfide, the principal zinc ore and a collector's gem when transparent crystals show intense colour and exceptional dispersion.
Mineralogy and crystal structure
Reference formula: ZnS. Sphalerite is the cubic zinc sulfide polymorph; wurtzite is the hexagonal dimorph. Transparent yellow, orange and red crystals can be highly valuable as specimens or collector gems. Sphalerite is classified with sulfides and has a cubic crystal system. Typical hardness is 3.5–4 on the Mohs scale and specific gravity is approximately 3.9–4.1.
Colour, lustre and habit
Typical colours include black, brown, yellow, orange, red, green. The usual tetrahedral, dodecahedral, massive habit and resinous, adamantine, metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Sphalerite forms in or is associated with hydrothermal sulfide veins, carbonate replacement deposits, skarns and sedimentary exhalative systems. Important documented localities include Spain, Peru, the United States, Mexico, Bulgaria, China and Canada.
Resinous lustre and extraordinary dispersion
Sphalerite is commercially unusual: dark ore is industrially important, while transparent crystals can show more fire than many familiar gems. Lustre, colour, clarity and locality drive collector value.
Collecting and care
Protect from scratches and cleavage breakage. Keep dry, avoid acids and determine specimen value before cutting transparent material.
