Sphalerite

Sphalerite is zinc sulfide (ZnS) and the most important ore of zinc. Its name comes from the Greek for treacherous, because its highly variable appearance, ranging from pale yellow and green to brown, red, and black, often confused early miners.

Most sphalerite is opaque to translucent with a resinous to adamantine luster, but rare transparent gem-quality crystals are cut for collectors. These gems show extraordinary dispersion (fire) far greater than diamond, though sphalerite is too soft for everyday jewelry.

Sphalerite commonly contains iron, and small amounts of cadmium, gallium, indium, and germanium, making it an important source of these elements as byproducts.

Sphalerite forms in a wide variety of ore deposits, most importantly in hydrothermal veins and in sediment-hosted and carbonate-hosted deposits known as Mississippi Valley-type deposits, where it occurs with galena, pyrite, and fluorite.

It also forms in contact metamorphic skarns and volcanogenic massive sulfide deposits. Sphalerite is typically deposited from hot, metal-rich fluids circulating through rock fractures and porous beds.

Major sources include deposits in the United States, Mexico, Peru, Australia, China, and Europe. Gem-quality transparent material comes from localities such as Spain and Mexico.

Sphalerite is identified by its resinous to adamantine luster, variable color, six directions of perfect cleavage, and a pale yellow to brown streak that often smells faintly of sulfur when scratched. Its hardness is 3.5-4.

The distinctive resinous luster and multiple cleavage directions help separate it from galena (heavier, gray, cubic cleavage) and from siderite or garnet. Transparent gem sphalerite shows intense fire.

Key tests: the brownish streak (lighter than the mineral itself), the sulfurous smell when scratched, and the resinous look. Its softness distinguishes gem sphalerite from harder lookalikes like garnet or zircon.

Sphalerite is the world's principal ore of zinc, mined to produce zinc for galvanizing steel, making brass, casting alloys, and manufacturing batteries and chemicals. It is also a major source of byproduct cadmium, gallium, indium, and germanium used in electronics.

Transparent gem-quality sphalerite is cut for collectors who prize its remarkable fire, though its softness and cleavage limit it to display rather than rings.

Metaphysically, sphalerite is associated with grounding and balancing energy, a traditional rather than scientific use.