sedimentary
Agate
Silicon dioxide (Quartz), SiO2
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, microcrystalline quartz structure (chalcedony), conchoidal fracture, specific gravity of 2.60 to 2.65, varying colors including white, brown, red, grey, and yellow often in banded patterns.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, microcrystalline quartz structure (chalcedony), conchoidal fracture, specific gravity of 2.60 to 2.65, varying colors including white, brown, red, grey, and yellow often in banded patterns.
Formation & geological history
Formed mainly by the deposition of silica from groundwater in the cavities of igneous rocks, such as vesicles in basalt, or in sedimentary rocks, over millions of years.
Uses & applications
Used in jewelry, decorative carvings, ornamental objects, mortars and pestles for laboratory use, and by collectors.
Geological facts
Agate was named by Theophrastus, a Greek philosopher, who discovered the stone along the shore of the Achates river in Sicily. Ancient civilizations used agates for seals, rings, and healing amulets.
Field identification & locations
Identified in the field by its characteristic concentric bands, waxy luster, and resistance to scratching by steel. Commonly found worldwide, especially in volcanic rock cavities and river gravels.
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