sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, varied colors due to impurities (white, gray, blue, black, green, red, brown), waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz crystal structure, conchoidal fracture with no true cleavage, and specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, varied colors due to impurities (white, gray, blue, black, green, red, brown), waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz crystal structure, conchoidal fracture with no true cleavage, and specific gravity of 2.60 to 2.65.
Formation & geological history
Formed primarily within the cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions in rhythmic bands over millions of years.
Uses & applications
Used extensively in jewelry, ornamental carvings, decorative items, and historically for precision instruments like mortar and pestles due to its durability.
Geological facts
Agates were named by the ancient Greek philosopher Theophrastus, after the Achates river (now the Dirillo) in Sicily, where stones were found.
Field identification & locations
Easily identified by its distinctive banded patterns and waxy luster. Commonly found worldwide in volcanic regions, river gravels, and glacial drift deposits.
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