mineral
Agate Geode
Cryptocrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 on Mohs scale; Color: Multi-colored bands (grey, white, brown) with a crystalline center; Luster: Vitreous to waxy; Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64
- Hardness
- 6
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Multi-colored bands (grey, white, brown) with a crystalline center; Luster: Vitreous to waxy; Structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64
Formation & geological history
Formed within cavities in igneous rocks (basalt) or sedimentary rocks when silica-rich groundwater precipitates layers of microscopic quartz crystals over millions of years. This specimen shows classic druzy quartz formation in the center.
Uses & applications
Extensively used in lapidary arts, jewelry (cabochons), interior decor, and as collectible museum specimens. Historically used for making mortars and pestles due to its hardness.
Geological facts
The banding in agates is caused by periodic changes in the concentration and composition of the silica-bearing fluids during deposition. Some geodes can contain liquid inclusions preserved for millions of years.
Field identification & locations
Identified by the distinct white/translucent banding (chalcedony) surrounding a hollow or crystal-filled center. Commonly found in Brazil, Uruguay, and the Lake Superior region. In the field, look for lumpy, rounded nodules with a weathered exterior that feels unusually light for their size.
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