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 FormulaSiO2.nH2O (hydrated silica) 1 Hardness (Mohs)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 Connections
Classified As
Entity-backed identity for the material classification this material already carries as an enum fact, pointing at the class subcategory of the same name. The enum fact itself stays on the entity unchanged.
In Discipline
In the Other Atlases
- Also in Divinity Atlas: Opal, mineral species of there.
Sources
1. Opal (Wikipedia)
Wikimedia FoundationOpal, 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.
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