sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brownish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brownish-tan
Luster: Dull to waxy

Identified June 12, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brownish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in marine environments from the accumulation of silica-rich organic remains like radiolarians or diatoms, or through chemical precipitation in limestone/chalk beds. Commonly Phanerozoic in age.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used as road aggregate, in landscaping, and as a low-cost lapidary material.

Geological facts

Because it breaks with a conchoidal fracture, it was one of the most important materials for prehistoric tool making. It is extremely chemically stable and resistant to weathering.

Field identification & locations

Identify in the field by its extreme hardness (scratches glass), waxy luster, and curved shell-like edges where broken. Commonly found as nodules in limestone regions.