|Mineral class||Silicates : quartz group.|
|Habitus||Ball formed aggregates, crusts, stalactites, massive or earthy.|
|Cleavage||None, conchoidal fracture.|
|Color||Usually colorless, white to bluis. Sometimes bluish black or red. Precious varietys have a rainbow colorplay.|
|Luster||Vitreous to greasy.|
|Occurance||Created by silica rich solutions at low temperatures. Commonly around hot springs.|
|Notes|| Often fluorescent in UV light.|
Insoluble in acids.
Decomposes when heated, giving off water, and may turn into quartz.
Sensitive against dehydration. It becomes fragile and could develop fractures when drying up.
|Locations|| A rare mineral in Sweden. No locality
is known of precious opal.|
| To silicate index.
|| Mineral group index.
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