錫石

Cassiterite is the principal ore of tin and the signature heavy mineral of the Xianghualing-Xuebaoding-Gejiu axis. Black or deep brown adamantine pyramids, often twinned into a dramatic visor or knee shape, define the species visually. China is both the largest producer of tin and the source of celebrated specimen material.

Notable varieties

• Visor twin / knee twin (twinned crystal)
• Wood tin (botryoidal habit)

The Chinese angle

The Xianghualing district in Hunan and Xuebaoding in Sichuan produce gem-quality cassiterite twins, often translucent reddish-brown, in matrix combinations with fluorite, beryl, and muscovite. Gejiu in Yunnan supplies the bulk industrial output.

Cassiterite — localities and judging quality

For specimens, the Xianghualing district in Hunan and Xuebaoding in Sichuan are the key Chinese sources — gemmy reddish-brown twinned crystals on muscovite or with fluorite and beryl — while the Gejiu tin district in Yunnan yields more opaque black material. Sharp “visor” or “knee” twins, adamantine lustre, translucency, and undamaged terminations drive value; the gemmy Xuebaoding twins are the most prized.