Cassiterite: The Heart of Tin
Cassiterite - SnO2 - is the primary ore mineral of tin and one of the most consequential economic minerals in human history. Bronze Age civilization ran on cassiterite long before anyone understood what it was.
Chemically it is tin dioxide, crystallizing in the tetragonal system. Cassiterite often forms as stubby prismatic crystals or twinned pairs with a characteristic elbow-twin V-shape (also called geniculate twinning). Its extreme density - specific gravity 6.8-7.1 - makes it easy to spot by weight alone, and easy to concentrate through simple gravity placer mining.
The name comes from the Greek kassiteros, the ancient word for tin. Cornwall, Bolivia, Malaysia, and Yaogangxian in China's Hunan Province are among the great tin districts of the world.
Key facts:
Chemistry: Tin dioxide, SnO2
- Mohs hardness: 6-7
- Specific gravity: 6.8-7.1 (very dense)
- Crystal system: Tetragonal
- Color: Dark brown to black, sometimes red or yellow; transparent when fresh
- Twin habit: Classic elbow / geniculate twin
Yaogangxian Mine in Hunan is world-famous for producing lustrous black cassiterite associated with fluorite, quartz, and arsenopyrite - some of the finest specimens on the market today.
