sedimentary
Chert (variations include Flint)
Sedimentary cryptocrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark grey to brownish; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Dark grey to brownish
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark grey to brownish; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Currently used as a gemstone (Jasper), in construction aggregate, and for starting fires (flint and steel).
Geological facts
Because of its extreme hardness and ability to hold a razor-sharp edge when fractured, it was the primary technology for tool-making for hundreds of thousands of years in human history.
Field identification & locations
Identify by its waxy appearance and conchoidal (shell-like) fracture patterns. It is very hard and will scratch glass. Look for it in limestone outcrops or as rounded pebbles in stream beds.
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