sedimentary

Chert (Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale. Color: Tan, grey, brown, or variegated (as seen in the specimen). Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: Tan, grey, brown, or variegated (as seen in the specimen)
Luster: Dull to waxy

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. Often found as nodules within limestone or chalk beds. Geological age can range from Precambrian to Holocene.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Currently used as a road aggregate, in abrasive manufacturing, and as a decorative stone for lapidary work.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be 'knapped' into extremely sharp blades. High-quality varieties like Flint were essential for early firearms (flintlocks).

Field identification & locations

Identify in the field by its hardness (will easily scratch glass) and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in outcroppings of sedimentary rock like limestone. Tips for collectors: look for 'nodules' that feel heavier than the surrounding rock.