sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness: 6.5 to 7 on the Mohs scale. Color: Varied, including white, gray, blue, red, orange, and brown, often in banded patterns. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.58 to 2.64.
- Hardness
- 6
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5 to 7 on the Mohs scale. Color: Varied, including white, gray, blue, red, orange, and brown, often in banded patterns. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.58 to 2.64.
Formation & geological history
Formed mainly in cavities of eruptive rocks or ancient lavas through the deposition of silica from groundwater solutions, often occurring in concentric layers over long periods.
Uses & applications
Used in ornamental objects, jewelry, carvings, and precision instruments such as mortar and pestle sets.
Geological facts
Agates are often associated with volcanic rocks and can preserve ancient environmental conditions in their intricate banding patterns.
Field identification & locations
Easily identified by its characteristic waxy luster, conchoidal fracture, and colorful concentric bands. Found worldwide, particularly in Brazil, Uruguay, India, and various US states.
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