mineral
Agate (Chert/Chalcedony)
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 (Mohs); Color: Tan, white, orange-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64
- Hardness
- 6
- Color
- Tan, white, orange-brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tan, white, orange-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64
Formation & geological history
Formed as a secondary mineral in volcanic or sedimentary rocks, often filling cavities (vesicles) or cracks via silica-rich groundwater. Frequently occurs in riverbeds or as glacial till deposits.
Uses & applications
Used in gemstone collecting, jewelry (cabochons), industrial abrasives, and historically for making tools (knapping).
Geological facts
The banding seen in the cross-section is characteristic of chalcedony. This specimen shows a thick weathered cortex (outer rind) hides the waxy silica interior.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture, waxy internal appearance, and its ability to scratch glass. Found globally in areas with volcanic history or ancient riverbeds.
