sedimentary
Agate
SiO2 (Chalcedony/Quartz)
Hardness: 6.5-7 on the Mohs scale. Color: White, grey, bluish, or yellowish translucent to opaque. Luster: Vitreous to waxy. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58-2.64.
- Hardness
- 6
- Color
- White, grey, bluish, or yellowish translucent to opaque
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on the Mohs scale. Color: White, grey, bluish, or yellowish translucent to opaque. Luster: Vitreous to waxy. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58-2.64.
Formation & geological history
Formed by the deposition of silica from groundwater in the cavities of igneous, sedimentary, or metamorphic rocks, often in concentric bands.
Uses & applications
Used widely in ornamental jewelry, decorative items, lapidary art, and precision instruments like mortars and pestles.
Geological facts
Agate is a variety of chalcedony and has been prized as an ornamental stone since ancient times, notably in ancient Greece and Rome for seals and rings.
Field identification & locations
Found worldwide, frequently in volcanic rock cavities (vesicles). Identify by its waxy luster, conchoidal fracture, and often banded appearance.
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