sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness: 6.5-7 on the Mohs scale, Color: various shades of white, gray, blue, purple, pink, red, and yellow, Luster: waxy to vitreous, Crystal structure: microcrystalline/trigonal, Cleavage: none, Specific gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 on the Mohs scale, Color: various shades of white, gray, blue, purple, pink, red, and yellow, Luster: waxy to vitreous, Crystal structure: microcrystalline/trigonal, Cleavage: none, Specific gravity: 2.6-2.7
Formation & geological history
Formed mainly by the deposition of silica from groundwater in the cavities of igneous and sedimentary rocks, often originating over millions of years in volcanic vesicles.
Uses & applications
Used for ornamental objects, jewelry, decorative carvings, and as a popular specimen for collectors.
Geological facts
Agates are a form of chalcedony quartz and have been prized since antiquity as gemstones and ornamental stones, famously used in ancient seals and signet rings.
Field identification & locations
Can be identified in the field by its characteristic concentric banding, waxy luster, and conchoidal fracture. Commonly found in stream beds, gravel deposits, and volcanic rock cavities worldwide.
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