sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray with yellow/tan band; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray with yellow/tan band
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray with yellow/tan band; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation in sedimentary environments. Common in marine limestone formations.
Uses & applications
Historically used for stone tools and arrowheads; currently used as aquarium gravel, road construction aggregate, or tumbled for lapidary jewelry.
Geological facts
Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's scalpel. Flint is a common name for the dark varieties of chert.
Field identification & locations
Identify in the field by its hardness (it should scratch glass) and its smooth, curved (conchoidal) fracture surfaces. Commonly found in stream beds or weathering out of limestone.
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