sedimentary

Chert (Flint/Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Brown, tan, or grey
Luster: Waxy to dull

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, or grey; 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 radiolarians or diatoms) or by chemical precipitation in saltwater environments. It commonly forms as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges; modern uses include road surfacing, jewelry (as jasper), and as a component in glass making.

Geological facts

Chert has a conchoidal fracture, meaning it breaks like glass, creating very sharp edges. It was one of the most important minerals for early humans to create tools and fire-starting kits.

Field identification & locations

Look for a smooth, waxy texture and curved, glass-like chip patterns (conchoidal fracture). It will easily scratch glass. Common in riverbeds and limestone outcrops globally.