sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely (brown, grey, white, red, etc.) due to impurities, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture, specific gravity of 2.58 to 2.64.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely (brown, grey, white, red, etc.) due to impurities, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture, specific gravity of 2.58 to 2.64.
Formation & geological history
Formed primarily within cavities of volcanic and metamorphic rocks through the deposition of silica-rich groundwater solutions in regular layers over long periods.
Uses & applications
Used in ornamental objects, jewelry, curing mortars, and as mineral specimens for collectors.
Geological facts
Agates are often found in ancient volcanic bubbles (vesicles) and have been prized as gemstones and amulets since ancient times, notably in ancient Greece and Egypt.
Field identification & locations
Can be identified by its distinctive banded patterns, waxy luster, and resistance to scratching by a steel knife. Commonly found in riverbeds, glacial drift deposits, and volcanic regions worldwide.
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