sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness: 6.5 to 7 on the Mohs scale. Color: Variable, often white, grey, blue, yellow, or brown with distinct concentric banding. 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: Variable, often white, grey, blue, yellow, or brown with distinct concentric banding. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.60 to 2.65.
Formation & geological history
Formed mainly within cavities of volcanic and metamorphic rocks through the slow deposition of silica-rich groundwater solutions over millions of years.
Uses & applications
Used extensively in jewelry, ornamental carvings, polished specimens, precision instrument bearings, and mortars and pestles.
Geological facts
Agate is one of the most popular stones used in lapidary art and has been prized as a gemstone and talisman since antiquity, notably by the ancient Greeks and Egyptians.
Field identification & locations
Easily identified by its characteristic curved or concentric banding and waxy luster. Commonly found worldwide in volcanic regions, river gravels, and ancient lava flows. Collectors look for unique fortification patterns and vibrant natural colors.
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