Cassiterite is the principal ore of tin. It is usually recovered from mines as black opaque grains, which are of little use in jewellery. Crystals are generally short, stubby prisms. Occasionally, rare, transparent, reddish brown crystals with adamantine lustre are found and faceted for collectors. They could be confused with diamond, brown zircon, and sphene, but for the higher specific gravity and distinct dichroism.

Cassiterite occurs in pegmatites and can be washed into alluvial deposits. Localities include the Malay Peninsula, England, Germany, Australia, Bolivia, Mexico and Namibia.

The name "cassiterite" comes from the Greek word, kassiteros, meaning tin.