Any of the gem varieties
of corundum except those which, being red
are called ruby; blue sapphires are best-known,
but most other colors, produced by impurities of iron and titanium, are
known. The best sapphires come from Kashmir, Myanmar, Thailand, Sri Lanka,
and Australia. Synthetic stones, made by flame-fusion, are used for jewel
bearings, phonograph styluses, etc.
AND PLANETARY SCIENCE