sedimentary
Chert (often called Flint or River Stone)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, white, and mottled brown; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white, and mottled brown
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white, and mottled brown; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows water-worn rounded edges, indicating it was transported by a river or stream.
Uses & applications
Historically used for stone tools and starting fires; currently used in road construction, landscaping, and occasionally as an abrasive.
Geological facts
Chert is so hard that it can scratch glass and steel. It was one of the most important materials for prehistoric humans to create sharp-edged tools like arrowheads and knives.
Field identification & locations
Identify in the field by its hardness and its smooth, curved (conchoidal) breaks. Often found in riverbeds or as nodules weathering out of limestone.
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