sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness: 6.5 to 7 on the Mohs scale; Color: Varies widely including purple, white, brown, and reddish tones due to impurities; 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 purple, white, brown, and reddish tones due to impurities; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline quartz); Cleavage: None; Specific gravity: 2.60 to 2.65
Formation & geological history
Formed primarily within cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions in rhythmic layers over long periods.
Uses & applications
Used in ornamental objects, jewelry, tumbled stones, and precision instruments such as mortar and pestles.
Geological facts
Agate is one of the most popular and historically significant lapidary stones, known for its distinct concentric banding patterns named after the Achates River in Sicily.
Field identification & locations
Easily identified by its characteristic curved color banding and waxy luster. Found worldwide, particularly in Brazil, Uruguay, India, and the United States.
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