Chromium

Chromium is a hard, bright metal that takes a mirror polish. Its name comes from the Greek for color, because its compounds come in vivid shades; it gives rubies their red and emeralds their green. It is mined as chromite ore, mostly in South Africa and Kazakhstan.

Most chromium goes into stainless steel. With at least about 10.5% chromium, steel forms an invisible oxide skin that stops rust and repairs itself when scratched. Chromium is also plated onto car parts and taps as shiny chrome, and its compounds are used in pigments and leather tanning. Some forms, such as hexavalent chromium, are toxic and tightly controlled.