sedimentary
Chert (Flint variety)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically grey, black, or brown with a weathered outer rind; Luster: waxy to dull; Crystal structure: hexagonal (Microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically grey, black, or brown with a weathered outer rind
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, black, or brown with a weathered outer rind; Luster: waxy to dull; Crystal structure: hexagonal (Microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains such as radiolaria or diatoms on the seafloor, or via chemical precipitation within limestone/chalk beds through various geological ages.
Uses & applications
Historically used for stone tools (arrowheads, knives) and strike-a-lights for fire making. Modernly used as road aggregate or in landscaping.
Geological facts
Flint was one of the most important minerals for early human survival due to its ability to produce sharp edges when knapped and sparks when struck against steel or iron pyrites.
Field identification & locations
Identify in the field by its very smooth, glass-like 'conchoidal' (curved) fracture surfaces and its ability to scratch glass. It is common in riverbeds and limestone outcrops globally.
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