sulfides
Sphalerite
ZnS
- Also known as
- zinc blendeblack jack
- Crystal system
- cubic
- Hardness
- 3.5–4 on the Mohs scale
- Lustre
- resinous
- Colour
- Yellow, brown, red, black, occasionally colourless
- Where it forms
- In hydrothermal veins with galena, and in sedimentary carbonate-hosted deposits.
- Chiefly from
- Picos de Europa, SpainMissouri and Tennessee, United StatesBulgariaPeru
Why it is that colour
Iron substituting for zinc. Iron-free sphalerite is nearly colourless; more iron darkens it through honey and red to black.
Safety
Zinc sulfide is relatively benign as sulfides go, but sphalerite commonly contains cadmium substituting for zinc, and cadmium is seriously toxic. It also releases hydrogen sulfide if treated with acid. Handle normally, do not powder, do not put in water.
Where it comes from
The principal ore of zinc, and the world’s main source of cadmium, gallium, germanium and indium, which are recovered from it as by-products. Those elements are essential to semiconductors and solar cells, which makes this mineral quietly central to modern electronics.
Historical use
Its name comes from the Greek for treacherous, because miners kept mistaking it for galena and finding it yielded no lead. The English name black jack carries the same frustration. Gem-quality sphalerite has extremely high dispersion, higher than diamond, but at hardness 4 it is too soft to wear.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
Worth knowing
Sphalerite is where germanium, gallium and indium come from — none of which are mined for their own sake, because none of them form ore deposits of their own. They substitute for zinc in trace amounts and are recovered from the residues of zinc smelting.
That has a consequence worth understanding: the supply of several elements critical to semiconductors, LEDs and solar panels is set by how much zinc the world happens to be smelting, not by demand for the elements themselves. Indium supply cannot simply be increased by wanting more indium.
Identity checked against IMA-CNMNC master list, June 2025.