sedimentary

Chert (variations include Flint)

Sedimentary cryptocrystalline quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified June 7, 2026More sedimentary →

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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.