sedimentary
Chert (Flint)
Chert (Microcrystalline or cryptocrystalline Quartz - SiO2)
Hardness: 7 Mohs scale; Color: Tan, brown, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal; Specific Gravity: 2.65.
- Hardness
- 7 Mohs scale
- Color
- Tan, brown, and dark grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, brown, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal; Specific Gravity: 2.65.
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation replacing limestone or dolostone.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include road surfacing and as a gemstone when colorful (Jasper).
Geological facts
Chert is so hard it can strike sparks against steel, which made its variety, flint, essential for early firearms like flintlocks. It is one of the most common materials used by prehistoric humans for tool-making.
Field identification & locations
Identify in the field by its waxy luster and smooth, curved (conchoidal) fracture surfaces that resemble glass. Often found as nodules within limestone beds.
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