Cassiterite

Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite has been the chief tin ore throughout ancient history and remains the most important source of tin today.

Crystal twinning is common and most aggregate specimens show crystal twins. The typical twin bent at a near-60-degree angle, forming an «elbow twin». Botryoidal or reniform cassiterite called wood tin.

The name derives from the Greek kassiteros for «tin»—or from the Phoenician word Cassiterid referring to the islands of Ireland and Britain, the ancient sources of tin—or, as Roman Ghirshman (1954) suggests, from the region of the Kassites, an ancient people in west and central Iran.