Opals

thumb|alt=A map of the world displaying the countries where opal is most commonly found; Australia, Ethiopia, Brazil, Mexico and the United States of America are highlighted.|Main opal producing countries

thumb|Geyserite from Iceland

Opallionectes andamookaensis (meaning "the opal swimmer from Andamooka") is the name given to a 5 m (16 ft) long cryptoclidian plesiosaur, which is thought to have lived during the early Cretaceous period (Lower middle Aptian), 115 million years ago, in shallow seas covering what is now Australia.

Fiorite is a hydrated silica mineraloid, a form of opal, found in cavities in volcanic tuff. It is a globular, botryoidal, or stalactic concretionary form of opal. The mineraloid has a pearly lustre and forms botryoidal masses. Named after Santa Fiora, Italy, fiorite is used as a gemstone.

thumb|right|A sample of hyalite thumb|right|fluorescence|Fluorescent hyalite under an [[ultraviolet blacklight]]

thumb|Cacholong, in the Geological Museum of Kiev University Cacholong, also known as Kalmuck agate, is a form of common opal, although it is often mistaken for agate or chalcedony, and Parker Cleaveland claimed it was a variety of chalcedony. It has a milky white colour that can also be described as bluish white or cream. With a Mohs hardness of about 6, it is used for carving, cameos, etc. The word "cacholong" has also been used as a synonym for actinolite.

thumb|10–20 mm pieces of tumble finishing|tumble-polished opalite, an artificial glass Opalite is a trade name for synthetic opalescent glass and various opal and moonstone simulants. Other names for this glass product include argenon, sea opal, opal moonstone, and other similar names. It is also used to promote impure varieties of variously colored common opal.

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