sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, colors vary widely including white, gray, blue, red, green, and yellow, waxy to vitreous luster, cryptocrystalline structure with indistinct 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, colors vary widely including white, gray, blue, red, green, and yellow, waxy to vitreous luster, cryptocrystalline structure with indistinct cleavage, specific gravity of 2.58 to 2.64.
Formation & geological history
Forms primarily within the cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions, often in concentric bands.
Uses & applications
Used for ornamental objects, jewelry, carvings, and precision instruments like mortars and pestles due to its durability.
Geological facts
Agate was highly prized in ancient civilizations as a talisman and for making seals, rings, and ornate vessels, with the city of Idar-Oberstein in Germany becoming a historic center for agate carving.
Field identification & locations
Can be identified by its distinctive conchoidal fracture, waxy luster, and concentric banding patterns; commonly found in volcanic regions worldwide.
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