sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including gray, white, blue, red, and brown, often banded. 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 gray, white, blue, red, and brown, often banded. 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-rich groundwater solutions in concentric layers over millions of years.
Uses & applications
Commonly used in jewelry, decorative ornaments, lapidary art, and occasionally for industrial pivot bearings and mortars.
Geological facts
Agate is one of the most popular materials used in lapidary arts. Ancient civilizations valued agates for their protective amulets and healing properties, dating back to the Neolithic period.
Field identification & locations
Identified by its waxy luster, conchoidal fracture, and distinctive curved banding patterns. Frequently found in riverbeds, beaches, and volcanic regions worldwide.
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