sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, brown, white, and grayish; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8.

Hardness: 6
Color: Tan, brown, white, and grayish
Luster: Dull to waxy

Identified June 9, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, white, and grayish; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8.

Formation & geological history

Formed primarily as a result of the accumulation of siliceous biological organisms on the sea floor or via the precipitation of silica in groundwater within existing sedimentary formations (nodular chert).

Uses & applications

Commonly used for road gravel, construction aggregate, and historically for stone tools like arrowheads and scrapers due to its sharp edges when fractured.

Geological facts

Chert has been used by humans for millions of years to create tools. Flint is a high-quality variety of chert. It is very resistant to chemical weathering.

Field identification & locations

Identify in the field by its hardness (will scratch glass), conchoidal fracture pattern, and dense, fine-grained appearance. Found worldwide in limestone and chalk deposits.