sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: typically gray, brown, or tan; Luster: dull to waxy; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.

Hardness: 7 on Mohs scale
Color: typically gray, brown, or tan
Luster: dull to waxy

Identified May 28, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically gray, brown, or tan; Luster: dull to waxy; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains such as radiolaria or diatoms on the seafloor, later undergoing lithification. Can also form by chemical precipitation in groundwater replacing other minerals.

Uses & applications

Historically used for stone tools like arrowheads and scrapers due to its sharp edges. Modernly used as road aggregate, in construction, and occasionally for lapidary work.

Geological facts

Chert is essentially the same material as flint, but the term flint is usually reserved for nodules found in chalk or marly limestone. It has been used by humans for millions of years to create tools.

Field identification & locations

Identified in the field by its hardness (will scratch glass), waxy luster, and its characteristic curved, shell-like (conchoidal) fracture patterns when broken. Commonly found in limestone and dolomite formations.