sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified April 1, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Commonly Paleozoic to Mesozoic in age.

Uses & applications

Historically used for stone tools and weapons; currently used as road aggregate, in construction, and occasionally as a gemstone (Jasper varieties).

Geological facts

Chert is essentially the same as flint, though 'flint' is often specifically used for chert found in chalk. It was one of the first materials humans traded over long distances in the Stone Age.

Field identification & locations

Identify by its waxy luster, extreme hardness (scratches glass), and shell-like curves (conchoidal fracture) when broken. Often found in nodules within limestone outcrops.