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

What Is Opal - Gemstone Facts and Information

Crystal Opal: Mineral information, data and localities.

Fire Opal: Mineral information, data and localities.

Opal: The mineral Opal (black, white, fire) information and pictures

Opal - Wikipedia

Association between opal occurrences and soil type and regolith type

Wax Opal: Mineral information, data and localities.

Opal: The mineral Opal (black, white, fire) information and pictures

Opal Mineral Information photos and Facts, Manganese Ore

Meet a Nevada Mineral: Opal - Nevada Mining Association

File:Precious opal (Berbere Hill, Ethiopia) 20.jpg - Wikipedia

Opal - Wikipedia

Precious opal (Mezezo area, Ethiopia) 6, Precious opal from…

File:Precious opal in basalt (Honduras) 2.jpg - Wikimedia Commons