CHEMISTRY

Sulfides — Galena, Pyrite, Sphalerite

Sulfide minerals — the chemistry built around sulfur as the dominant anion — are the world's principal source of base metals: lead (galena), zinc (sphalerite), copper (chalcopyrite, bornite), antimony (stibnite), and many others. They share metallic luster, often-perfect cleavage, and a vulnerability to oxidation that creates both their beauty and their preservation problems.

Galena

PbS, cubic. Perfect cubic crystals with three cleavages at right angles. Steel-grey metallic luster, dark grey streak. Specific gravity 7.6 — feels like lead because it IS lead. Famous localities: Tri-State (Missouri-Kansas-Oklahoma), Elmwood (Tennessee), Romania, Bulgaria, Sweden. Cabinet-size galena cubes are surprisingly heavy and very photogenic.

Pyrite

FeS₂, cubic. The 'fool's gold' — bright brassy yellow with metallic luster, but greenish-black streak (real gold streak is gold). Common habits: cubes (Spain's Navajún is famous for perfect striated cubes), pyritohedrons (12-sided 'soccer-ball' form), octahedrons. Daye-Hubei produces gleaming golden cubes with iridescent surface play. Pyrite oxidizes over decades — store dry to slow the reaction.

Sphalerite, chalcopyrite, stibnite

Sphalerite (ZnS) — resinous luster, six perfect cleavages produces a 'fire' from internal reflections in gem-quality pieces. Chalcopyrite (CuFeS₂) — brassier than pyrite, often heavily iridescent. Stibnite (Sb₂S₃) — orthorhombic acicular sword crystals, slate-grey metallic, soft (hardness 2). Lengshuijiang in Hunan is the world's premier stibnite locality, producing dramatic crystal swords up to 30 cm long.

← Back to Learn