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Opal

Silicate Minerals

Opal is a hydrated amorphous form of silica whose water content may range from 3 percent to 21 percent by weight and is usually between 6 percent and 10 percent. Because of its amorphous structure it is classified as a mineraloid, unlike the crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock. There are two broad classes, precious and common: precious opal displays play-of-color (iridescence) and common opal does not. The name is believed to come from the Sanskrit word upala, meaning jewel. In this atlas it is filed with the minerals as the species that opal gemstones record.

Facts
Kind
Mineral 1
Chemical Formula
SiO2.nH2O (hydrated silica) 1
Hardness (Mohs)
5.75 1
Commonly cited range is 5.5 to 6 on the Mohs scale; 5.75, the midpoint, is used here. Opal is a mineraloid, filed among the minerals because the atlas has no separate mineraloid kind.
Classification
Classification
Silicate Mineral 1
Use
Gemstone 1
Connections

Classified As

Silicate Minerals, Subcategories

In Discipline

Mineralogy, Disciplines
In the Other Atlases

Mineral Species Of

Opal

Also in Divinity Atlas: of this mineral species.

Found In

Australia

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Most precious opal to date has been mined in Australia.
Brazil

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Canada

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Guatemala

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Honduras

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Indonesia

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
New Zealand

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Peru

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Poland

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
United States

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Zambia

Also in Geography Atlas: where this subject is found.

Source Geology.com: Opal gemstoneArticle text
Quote, Article text
Precious opal is also mined in Brazil, the United States, Canada, Honduras, Indonesia, Zambia, Guatemala, Poland, Peru, and New Zealand
Sources
1. Opal (Wikipedia)
Wikimedia Foundation
  • Opal, lead paragraph
    Opal is a hydrated amorphous form of silica
  • Opal, article text
    Due to the amorphous (chemical) physical structure, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals.
View the Source
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