sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline crystal structure, translucent to opaque, specific gravity of 2.60 to 2.65, exhibits fine concentric banding or patterns.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline crystal structure, translucent to opaque, specific gravity of 2.60 to 2.65, exhibits fine concentric banding or patterns.
Formation & geological history
Formed mainly in cavities of volcanic and metamorphic rocks by the deposition of silica from groundwater solutions, typically in low-temperature environments over millions of years.
Uses & applications
Used in jewelry, ornaments, carving, lapidary art, mortars and pestles for laboratory use, and highly prized by rockhounds and mineral collectors.
Geological facts
Agate was named by Theophrastus, a Greek philosopher, after the Achates river in Sicily where the stones were first found.
Field identification & locations
Found worldwide, often in volcanic regions, riverbeds, and gravel deposits. Identify by its waxy luster, hardness that scratches glass, and characteristic banded patterns.
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