mineral
White Opal
Hydrated Silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness: 5.5-6.5 Mohs. Color: Milky white with varying degrees of translucency. Luster: Subvitreous to waxy. Crystal structure: Amorphous (non-crystalline). Cleavage: None. Specific gravity: 1.9-2.3.
- Hardness
- 5
- Color
- Milky white with varying degrees of translucency
- Luster
- Subvitreous to waxy
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Physical properties
Hardness: 5.5-6.5 Mohs. Color: Milky white with varying degrees of translucency. Luster: Subvitreous to waxy. Crystal structure: Amorphous (non-crystalline). Cleavage: None. Specific gravity: 1.9-2.3.
Formation & geological history
Formed from the deposition of silica-rich water in crevices or voids within sedimentary or volcanic rocks. It typically forms at relatively low temperatures over millions of years.
Uses & applications
Primarily used in jewelry as gemstones (cabochons), and highly valued as mineral specimens by collectors. Low-grade opal can be used as an abrasive or in ceramics.
Geological facts
Opal is a mineraloid because it does not have a crystalline structure. It contains between 3% and 21% water by weight. Known as the birthstone for October.
Field identification & locations
Identify in the field by its waxy luster, conchoidal fracture (curved breaks), and lack of crystal faces. It is commonly found in Australia, Ethiopia, and the Western USA. Look for milky, translucent nodules in basalt or sandstone seams.
