Opal: Mineral information, data and localities.

Although it is still (2007) regarded as a mineral species for historical reasons, opal is not a true mineral in the accepted sense of the word as it is

Polished Green Opal Standing Free Form x 12 From Antsirabe, Madagascar

Opal Geoscience Australia

Opal : Properties, Formation, Uses and Deposits » Geology Science

Precious Opal: Mineral information, data and localities.

Opal-C: Mineral information, data and localities.

Opal : Properties, Formation, Uses and Deposits » Geology Science

Green Jelly Opal (rare color and locality)

Opal (Common) Gem Guide and Properties Chart

Opal: Mineral information, data and localities.

Opal – WGNHS – UW–Madison

Opal, Properties, Types & Uses