Iron-black to brownish-black color,
dark-brown streak, metallic to submetallic luster.
Mohs hardness 5.5.
Habit: massive, granular, nuggets.
Color: black or brownish black.
Luster: metallic.
Diaphaneity: opaque.
Streak: brown.
Cleavage: none.
Twinning: {111}.
Fracture: uneven to
conchoidal.
Others: weakly magnetic.
Thermal conductivity of 1.73–2 W.m–1K–1
Only commercial source of chromium and its
compounds.
A natural oxide of ferrous iron and chromium, sometimes with magnesium and aluminum present. Usually occurs in magnesium and iron-rich igneous
rocks.
Only commercial source of chromium used in the metallurgical industry (85%) mainly as Fe–Cr for steelmaking, in the refractory and foundry market (8%) and in the chemical industry (7%).
Confirmed human
carcinogen during ore processing. Human
mutation data reported. See also
CHROMIUM COMPOUNDS and IRON.
