sedimentary
Chert (v. Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, or brownish-grey with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Color
- tan, grey, or brownish-grey with waxy luster
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, or brownish-grey with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed by precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or diatoms) in marine environments. Found in Paleozoic to Cenozoic sedimentary layers.
Uses & applications
Historically used for making stone tools (knapping) due to sharp edges. Today used in construction aggregate, road surfacing, and as a decorative stone in landscaping.
Geological facts
Because it breaks with a conchoidal fracture like glass, it creates edges sharper than a steel scalpel. Flint is a specific dark variety of chert often found in chalk or marly limestone.
Field identification & locations
Identify by its waxy look, hardness (it will scratch glass), and the way it breaks into curved, sharp flakes. Common in limestone outcrops and riverbeds.
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