gemstone
Agate
Chalcedony (SiO2)
Hardness of 6.5-7 on the Mohs scale, varied colors including gray, blue, white, and brown, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, 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, varied colors including gray, blue, white, and brown, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, no true cleavage, specific gravity of 2.58-2.64.
Formation & geological history
Formed mainly in cavities of volcanic and metamorphic rocks by the deposition of silica from groundwater solutions in rhythmic layers over long periods.
Uses & applications
Used in jewelry, ornamental carvings, decorative items, and historically for precision instruments like mortar and pestles due to its hardness.
Geological facts
Agate was named by Theophrastus, a Greek philosopher, after the Achates River in Sicily where stones were found in ancient times.
Field identification & locations
Easily identified by its characteristic concentric bands and waxy luster. Found worldwide, particularly in Brazil, Uruguay, India, and the USA.
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