gemstone
Opal
Hydrated amorphous silica (SiO2·nH2O)
AI-generated identification · may be incorrectMohs hardness of 5.5 to 6.5, displays play-of-color, vitreous to greasy luster, amorphous crystal structure.
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Physical properties
Mohs hardness of 5.5 to 6.5, displays play-of-color, vitreous to greasy luster, amorphous crystal structure.
Formation & geological history
Forms from a solution of silicon dioxide and water seeping into cracks and voids, typically in sedimentary environments.
Uses & applications
Used primarily in fine jewelry, carving, and as collector specimens.
Geological facts
Opal's unique play-of-color is caused by the diffraction of light through microscopic silica spheres within its structure.
Field identification & locations
Identified by its characteristic iridescence and lack of crystal cleavage; commonly found in Australia and Ethiopia.
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