High purity (99.999 % = 5N) chromium crystals, produced by chemical transport reaction through decomposition of chromium iodides, as well as a high purity (99,95 % = 3N5) 1 cm 3 chromium cube for comparison. — Photo: Alchemist-hp ( talk ) ( www.pse-mendelejew.de ) · FAL
Chromium
A steely-grey, hard transition metal (symbol Cr, atomic number 24) prized for corrosion resistance — it makes stainless steel stainless.
Intro adapted from Wikipedia (CC BY-SA).
Chromium is an IMA-recognized mineral species in the native element class, with the chemical formula Cr.
It crystallizes in the cubic crystal system (space group Fm3m). It is a member of the Iron structural group.
Key properties: specific gravity 7.17; Metallic. R: (480) 65.3, (546) 67.9, (589) 68.8, (656) 70.0 luster.
IMA symbol Cr, IMA status: approved, named in 1980.
Found in heavy sands derived from the contact metamorphic zone between a siliceous marble and ultramafic rock (Sichuan Province, China); in a kimberlite pipe (Liaoning Province, China); in podiform chromitites (Luobusha ophiolite, China).
It is found associated with Pyrrhotite, pentlandite, chalcopyrite, platinum group minerals, danbaite (Sichuan Province, China); cohenite, moissanite, ilmenite.
Its name comes from the Greek chroma, color, as all chromium compounds are colored.