sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness of 6.5-7 on the Mohs scale, variable colors featuring distinct banding, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of 2.58-2.64.
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Physical properties
Hardness of 6.5-7 on the Mohs scale, variable colors featuring distinct banding, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of 2.58-2.64.
Formation & geological history
Formed mainly in cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions, often layer by layer over millions of years.
Uses & applications
Used in ornamental objects, jewelry, carvings, display specimens, and formerly in precision instruments like mortar and pestles.
Geological facts
Agate was highly prized as a gemstone in ancient civilizations like Ancient Greece and Egypt, frequently used in signet rings and ornate talismans.
Field identification & locations
Easily identified by its characteristic concentric bands of color and waxy luster; commonly found worldwide in volcanic regions, river gravels, and ancient lava flows.
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