sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including white, brown, red, grey, blue, black, yellow, and orange. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.60 to 2.65.
- Hardness
- 6
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including white, brown, red, grey, blue, black, yellow, and orange. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.60 to 2.65.
Formation & geological history
Formed primarily within metamorphic and igneous rocks by the deposition of silica from groundwater in cavity walls, often over millions of years.
Uses & applications
Used in ornamental objects, jewelry, tumbled stones, decorative carvings, and precision instruments like mortars and pestles due to its hardness.
Geological facts
Agate is one of the most popular materials used in hardstone carving and has been used since ancient times, such as by the ancient Greeks and Romans for seal rings and amulets.
Field identification & locations
Can be identified in the field by its waxy luster, conchoidal fracture, and characteristic concentric banding. Commonly found in volcanic rock cavities worldwide.
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