sedimentary
Agate Nodule
Silicon dioxide (Chalcedony/Quartz), SiO2
Hardness: 6.5-7 on the Mohs scale; Color: Varies with white, brown, and translucent banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline quartz); Specific gravity: 2.60-2.65
- Hardness
- 6
- Color
- Varies with white, brown, and translucent banding
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on the Mohs scale; Color: Varies with white, brown, and translucent banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline quartz); Specific gravity: 2.60-2.65
Formation & geological history
Formed in cavities of volcanic or sedimentary rocks through the deposition of silica from groundwater circulating over long geological periods.
Uses & applications
Used in ornamental objects, jewelry, lapidary arts, and as collector specimens.
Geological facts
Agate is a variety of chalcedony that often forms concentric bands inside hollow cavities of rocks, reflecting changes in the water's mineral content during formation.
Field identification & locations
Identified by its microcrystalline structure, conchoidal fracture, waxy luster, and resistance to steel. Commonly found in gravel beds, volcanic regions, and stream beds worldwide.
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