mineral
Opal
SiO2·nH2O
AI-generated identification · may be incorrectMohs hardness 5.5-6.5; displays a unique play-of-color; vitreous to sub-resinous luster; amorphous crystal structure.
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Physical properties
Mohs hardness 5.5-6.5; displays a unique play-of-color; vitreous to sub-resinous luster; amorphous crystal structure.
Formation & geological history
Formed from a solution of silicon dioxide and water seeping into cracks and voids, commonly found in sedimentary environments.
Uses & applications
Extensively used in high-end jewelry, gemstone collections, and ornamental carvings.
Geological facts
Opal contains up to 21% water content and its iridescence is caused by the diffraction of light through microscopic silica spheres.
Field identification & locations
Identified easily by its distinctive play-of-color and lower hardness compared to quartz; major deposits are found in Australia and Ethiopia.
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Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
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Granite
Granite (Phaneritic intrusive igneous rock)
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