sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, varied colors including gray, white, blue, brown, and yellow, waxy to vitreous luster, cryptocrystalline structure (microscopic quartz fibers), conchoidal fracture with no true cleavage, specific gravity of 2.58 to 2.64.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, varied colors including gray, white, blue, brown, and yellow, waxy to vitreous luster, cryptocrystalline structure (microscopic quartz fibers), conchoidal fracture with no true cleavage, specific gravity of 2.58 to 2.64.
Formation & geological history
Formed mainly in cavities of volcanic and metamorphic rocks through the slow deposition of silica-rich groundwater solutions over millions of years.
Uses & applications
Used in ornamental objects, jewelry, gemstone carving, precision pendulum supports, mortars and pestles, and as collector specimens.
Geological facts
Agate bands represent successive layers of silica deposition inside ancient gas cavities in lava. It is named after the Achates River in Sicily.
Field identification & locations
Can be identified in the field by its waxy luster, micro-banded patterns, conchoidal fracture, and resistance to scratching by a steel knife. Commonly found in river gravels, volcanic regions, and desert environments worldwide.
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