sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Brown, grey, black (dark varieties often called flint); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Brown, grey, black (dark varieties often called flint)
Luster: Waxy to dull

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brown, grey, black (dark varieties often called flint); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed via the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like diatoms or sponges) in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road construction, as an abrasive, and occasionally for lapidary work.

Geological facts

Flint was arguably the most important mineral in human history for its ability to produce sharp edges for tools and sparks for making fire. It breaks with a distinctive conchoidal (shell-like) fracture.

Field identification & locations

Look for smooth, waxy surfaces and curved, glass-like breakage patterns. It is harder than steel and will scratch a glass plate. Commonly found in riverbeds or eroding out of limestone cliffs.