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 - Wikipedia

e-Rocks Mineral Auctions

Opal / (variety - “Opal-AN”) / (variety - “Hyalite Opal”) / (“Blood Vessel Opal”) / Locality - San Luis Potosi, Mexico

Opal - Wikipedia

Opal-C: Mineral information, data and localities.

Pink Opal: Mineral information, data and localities.

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

Precious Opal: Mineral information, data and localities.

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

Opal-A: Mineral information, data and localities.

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

Meet a Nevada Mineral: Opal - Nevada Mining Association