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

Opal (Common) Gem Guide and Properties Chart

Gold Opal: Mineral information, data and localities.

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

Opal - Wikipedia

Opal-An (hyalite opal) from Zacatecas, Mexico. (A) Natural light. (B)

Opal, Properties, Types & Uses

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

Association between opal occurrences and soil type and regolith type

Opal: Mineral information, data and localities.

Precious Opal: Mineral information, data and localities.

Green Jelly Opal (rare color and locality)

Polished Complex Wispy Green Opal Standing Free Forms x 3 From Antsirabe, Madagascar

Opal-AN (Hyalite Opal) with Carbonate-rich Fluorapatite (var: Staffelite) / Locality - Valec (Waltsch), Bohemia, Czech Republic

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

What Is Opal - Gemstone Facts and Information