sedimentary
Agate
Silicon dioxide (chalcedony variety), SiO2
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely including brown, red, grey, and white, 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 including brown, red, grey, and white, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture, specific gravity of 2.58 to 2.64.
Formation & geological history
Formed mainly by the deposition of silica from groundwater in the cavities of igneous and sedimentary rocks. Can range in geological age from Precambrian to recent.
Uses & applications
Used for ornamental objects, jewelry, tumbled stones, leather-working burnishers, and scientific mortars and pestles.
Geological facts
Agate is often found filling vesicles in volcanic rocks. Ancient civilizations used agates for healing amulets and ornate seals.
Field identification & locations
Identified in the field by its waxy luster, conchoidal fracture, and sometimes concentric banding. Commonly found in riverbeds, gravel deposits, and volcanic regions worldwide.
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