Bismuthinite — Bi₂S₃ — is the principal ore of bismuth and one of the most unusual sulfide minerals in any collection. This specimen comes from Inner Mongolia, where acicular (needle-like) crystals form in hydrothermal veins cutting through granite and skarn rocks.
What makes bismuthinite special:
• Silvery-gray to tin-white metallic luster that tarnishes to iridescent bronze over time
• Perfect cleavage in one direction — splits into fine blades
• Softer than most sulfides (Mohs 2) — can scratch with a fingernail
• The densest common sulfide (bismuth is a heavy metal atom)
• Produces bismuth metal — used in pharmaceuticals (Pepto-Bismol), solders, and the famous iridescent hopper crystals grown by collectors
Bismuth itself is fascinating — its nucleus was long believed stable, but in 2003 physicists discovered it’s actually weakly radioactive with a half-life longer than the age of the universe. So every bismuthinite crystal is, very slowly, becoming thallium.
