sedimentary
Chert (Chalcedony/Agate variety)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale). Color: Waxy white to tan/translucent. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6.
- Hardness
- 6
- Color
- Waxy white to tan/translucent
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale). Color: Waxy white to tan/translucent. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6.
Formation & geological history
Formed through the precipitation of silica-rich fluids within sedimentary rock cavities or by the replacement of carbonate minerals. Often found in limestone or volcanic environments.
Uses & applications
Used historically for stone tools due to its sharp conchoidal edges; currently used for lapidary work, jewelry (as agate), and as an abrasive in some industrial processes.
Geological facts
This specimen shows the characteristic 'conchoidal fracture'—curved, shell-like break patterns—which made it the ideal material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy appearance, its ability to scratch glass, and its sharp, curved edges when broken. Commonly found in desert pavement or eroded out of limestone beds.
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