sedimentary
Chert (and Jasper/Chalcedony variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and yellowish-orange. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Tan, brown, and yellowish-orange
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and yellowish-orange. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians) or chemical precipitation from hydrothermal fluids in sedimentary environments. Can be of any geological age from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads). Today used for landscaping, as semi-precious gemstones when colorful (Jasper), and in some industrial grinding applications.
Geological facts
Chert is so hard it can create sparks when struck against steel. It is one of the most common materials used by prehistoric humans for tool-making due to its predictable conchoidal fracture.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth texture with rounded, shell-like fracture surfaces. Often found in riverbeds or within limestone formations.
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