sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7.0 (Mohs); Color: Brown, gray, and tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture).

Hardness: 7
Color: Brown, gray, and tan
Luster: Waxy to vitreous

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 7.0 (Mohs); Color: Brown, gray, and tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Forms through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation from groundwater within limestone or chalk beds.

Uses & applications

Historically used for stone tools and strike-a-lights; currently used in construction aggregate and as a collector's specimen.

Geological facts

Chert has been used by humans for millions of years to create sharp-edged tools like arrowheads because of its predictable conchoidal fracturing.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and sharp, shell-like fracture edges. Commonly found in nodular form within carbonate rocks.