mineral
Polished Agate Geode
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 (Mohs). Color: Translucent grey, white, and brown with concentric banding. Luster: Vitreous to waxy. Structure: Trigonal/Microcrystalline. Specific Gravity: 2.60-2.65.
- Hardness
- 6
- Color
- Translucent grey, white, and brown with concentric banding
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Translucent grey, white, and brown with concentric banding. Luster: Vitreous to waxy. Structure: Trigonal/Microcrystalline. Specific Gravity: 2.60-2.65.
Formation & geological history
Formed in cavities (vesicles) of volcanic or sedimentary rocks where silica-rich groundwater deposited layers of chalcedony over thousands of years.
Uses & applications
Ornamental display, healing crystals, jewelry making, bookends, and collection specimens.
Geological facts
Agate is named after the Achates River in Sicily where it was first discovered. This specimen is a 'solid' geode, or nodule, where the silica has completely filled the interior cavity.
Field identification & locations
Identify by distinct concentric color bands and a rough, cauliflower-like outer basalt/rhyolite crust. Common in Brazil, Uruguay, and the United States (Oregon/lake Superior).
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