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

Gold Opal: Mineral information, data and localities.

Minerals, Free Full-Text

File:Black opal (Stayish Mine, Wollo Province, Ethiopia) 6 (23226115484).jpg - Wikipedia

Rare $675,000 opal makes public debut

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

Map showing distribution of opal bearing localities in Western Queensland [cartographic material] / - Catalogue

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

Green Jelly Opal (rare color and locality)

Opal-AG: Mineral information, data and localities.