sedimentary
Agate
Chalcedony (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely including brown, white, red, grey, and yellow due to impurities, waxy to vitreous luster, cryptocrystalline crystal structure, no cleavage (conchoidal fracture), specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely including brown, white, red, grey, and yellow due to impurities, waxy to vitreous luster, cryptocrystalline crystal structure, no cleavage (conchoidal fracture), specific gravity around 2.60 to 2.65.
Formation & geological history
Formed primarily within cavities of volcanic and metamorphic rocks through the deposition of silica-rich groundwater solutions in concentric layers over geological time.
Uses & applications
Used in ornamental objects, jewelry, polished specimens, curing mortars, and as collector mineral pieces.
Geological facts
Agate is one of the most popular and varied forms of chalcedony. The concentric banding patterns reflect changes in the solutions that formed them over millions of years.
Field identification & locations
Easily identified by its distinct waxy luster, hardness (scratches glass), and often banded appearance. Frequently found in riverbeds, beaches, and volcanic regions worldwide.
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