sedimentary
Agate
Chalcedony (SiO2)
Hardness: 6.5 to 7 on the Mohs scale, Color: Various including white, gray, blue, red, orange, and brown, Luster: Waxy to vitreous, Crystal structure: Trigonal (microcrystalline quartz), Cleavage: None, Specific gravity: 2.6 to 2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5 to 7 on the Mohs scale, Color: Various including white, gray, blue, red, orange, and brown, Luster: Waxy to vitreous, Crystal structure: Trigonal (microcrystalline quartz), Cleavage: None, Specific gravity: 2.6 to 2.7
Formation & geological history
Formed mainly by the deposition of silica from groundwater in the cavities of igneous and sedimentary rocks, often developing in concentric bands over millions of years.
Uses & applications
Used in ornamental objects, jewelry, polished specimens, mortars and pestles for laboratory use, and by collectors.
Geological facts
Agate is one of the most popular and widespread varieties of chalcedony, named by Theophrastus after the Achates River in Sicily where stones were found in ancient times.
Field identification & locations
Identified easily by its distinctive banded patterns and waxy luster; commonly found in volcanic rock cavities (lithophysae) and river gravels worldwide.
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