Opal is the One of the most popular gems and found in many locations. Major suppliers include Australia, Brazil, Mexico, Czechoslovakia (formerly in Hungary), Nevada.

Fine opals in large sizes are rare and costly, especially black opal. Usually cut as cabochons, sometimes beads. Occasionally found as fossilized (opalized) clamshells, snail shells, or wood.

Transparent opals, such as Mexican red or orange fire opal, are often faceted. Values are normally determined by the presence and nature of color flashes.