An iron-magnesium silicate of the pyroxene family. The metallic lustre across its surface comes from micro-thin layers of iron reflecting light—an effect called "schiller," named after shot silk.

Found in ultramafic rock formations in South Africa, Brazil, and Austria. Formed near the Earth's mantle, deep enough that its presence at the surface is an anomaly.

Ancient Rome used it to ornament armour. It looks like metal, but it is mineral. Pick it up, and it is lighter than expected. What the eye sees and what the hand feels do not agree.