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Mineral

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.

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
Chemical Formula
SiO2.nH2O (hydrated silica) 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.
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.
Colour
Colourless or White 2
Colour
Colourless or White 2
Colour
Grey or Black 2
Colour
Grey or Black 2
Colour
Brown 2
Colour
Brown 2
Colour
Red or Pink 2
Colour
Red or Pink 2
Colour
Orange or Yellow 2
Colour
Orange or Yellow 2
Colour
Green 2
Colour
Green 2
Colour
Blue or Purple 2
Colour
Blue or Purple 2
Lustre
Vitreous 2
Lustre
Vitreous 2
Lustre
Pearly 2
Lustre
Pearly 2
Lustre
Resinous 2
Lustre
Resinous 2
Lustre
Waxy or Greasy 2
Lustre
Waxy or Greasy 2
Classification
Strunz Class
Silicates 1
Strunz Class
Silicates 1
Use
Gemstone 1
Use
Gemstone 1
Connections

Caused By

Biomineralization, Processes
Source Opal (Wikipedia)
Hydrothermal Mineral Deposition, Processes
Source EBSCO Research Starters: Hydrothermal solutions and mineralization

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
2. minerals.net: Opal
minerals.net
  • Color field
    Colorless, white, yellow, orange, red, purple, blue, green, gray, brown, and black. These are some of the base colors of Opal. Certain opals display different colors when viewed from different directions, or when the stone is turned, or when the light source is moved. This phenomenon, called play of color, gives a stone color flashes, or schiller s of different colors which vary from stone to stone.
  • Luster field
    Usually vitreous, but may also be pearly, waxy, or resinous.
View the Source
Opal (Wikipedia)
Caused By: Biomineralization, Varieties of common opal
Quote, Caused By: Biomineralization, Varieties of common opal
Opal is also formed by diatoms.
View the Source
EBSCO Research Starters: Hydrothermal solutions and mineralization
EBSCO Research StartersCaused By: Hydrothermal Mineral Deposition, Hydrothermal deposit types and gangue minerals
Quote, Caused By: Hydrothermal Mineral Deposition, Hydrothermal deposit types and gangue minerals
Gangue minerals include barite, fluorite, chalcedony, opal, calcite, and aragonite.
View the Source
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