sedimentary
Chert (often called Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, brown, or white; Luster: waxy to dull; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale), Color: tan, grey, brown, or white
- Color
- tan, grey, brown, or white
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, brown, or white; Luster: waxy to dull; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from aqueous fluids, often replacing carbonate materials in sedimentary limestone or chalk beds, or as bedded deposits of radiolarian or diatomaceous remains.
Uses & applications
Used historically for stone tools and projectiles; currently used as road aggregate, in glass manufacturing, and as a decorative stone.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be knapped into sharp edges for arrowheads and knives.
Field identification & locations
Look for a glassy or waxy interior that contrasts with a rougher outer cortex; it will scratch glass and produce sparks when struck against steel. Found globally in limestone formations.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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