A common mineral, formed at high-temperatures as an accessory in
igneous rocks, principally
basalts,
kimberlites,
peridotites, and in
xenoliths; in regionally metamorphosed aluminum-rich
schists; in regionally and contact metamorphosed
limestones (
Anthony et al., 2001—2005). The largest specimens include:
Samarian spinel, over 500 carats, stored in the Central Bank of Iran, Tehran; 398.72 carat red spinel purchased in China in 1676 and stored in the Diamond Fund, Moscow;
Timur ruby, 361 carats, part of the Crown Jewels of the United Kingdom.
