mineral
Agate Geode
Silicon Dioxide (SiO2) - Banded Chalcedony
AI-generated identification · may be incorrectHardness: 6.5-7 on Mohs scale; Color: Gray, tan, and white translucent bands; Luster: Vitreous to waxy; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None; Specific gravity: 2.58-2.64
- Hardness
- 6
- Color
- Gray, tan, and white translucent bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, and white translucent bands; Luster: Vitreous to waxy; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None; Specific gravity: 2.58-2.64
Formation & geological history
Formed by the deposition of silica from groundwater in cavities within volcanic or sedimentary rocks. Over time, layers of microcrystalline quartz create the characteristic banding. These can range from millions to several hundred million years old.
Uses & applications
Used primarily for ornamental purposes, jewelry (lapidary), as collector specimens, and historically for making burnishers or mortars and pestles.
Geological facts
The word 'agate' comes from the Achates River in Sicily, where agates were first discovered. No two agates are exactly alike due to the unique minerals present during their layered formation.
Field identification & locations
Identify by its translucent banding and waxy texture when cut. In the field, look for nondescript, rounded nodules with a rough, 'cauliflower' or pitted exterior surface. Found globally, with major deposits in Brazil, Uruguay, and the United States (Lake Superior region).
