mineral
Common Opal
Hydrated Amorphous Silica (SiO2·nH2O)
AI-generated identification · may be incorrectHardness of 5.5-6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure with no cleavage, and specific gravity around 2.1.
Identified More mineral →
Explore Common Opal in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 5.5-6.5 on the Mohs scale, waxy to vitreous luster, amorphous crystal structure with no cleavage, and specific gravity around 2.1.
Formation & geological history
Forms via low-temperature precipitation from silica-rich aqueous solutions in volcanic or sedimentary environments.
Uses & applications
Used primarily in lapidary work, cabochons, and ornamental carvings by mineral collectors.
Geological facts
Unlike precious opal, common opal lacks the characteristic play-of-color due to its disorganized microscopic silica spheres.
Field identification & locations
Identified by its conchoidal fracture, lack of cleavage, and dull or waxy appearance, often found filling cavities in volcanic host rocks.
More like this
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