mineral
Common Opal
Hydrated amorphous silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness of 5.5 to 6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure with conchoidal fracture, and specific gravity around 2.1.
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Physical properties
Hardness of 5.5 to 6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure with conchoidal fracture, and specific gravity around 2.1.
Formation & geological history
Forms via the precipitation of silica-rich groundwater within volcanic or sedimentary rocks at low temperatures.
Uses & applications
Primarily used as a lapidary stone for cabochons, carvings, and specimen collecting.
Geological facts
Unlike precious opal, common opal lacks the characteristic play-of-color, though it often exhibits pleasing milky or dendritic patterns.
Field identification & locations
Identify by its conchoidal fracture and lack of cleavage, typically found in volcanic cavities and sedimentary beds worldwide.
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Other mineral specimens
Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Granite
Granite (Phaneritic intrusive igneous rock)
igneous