sedimentary

Chert (and Flint variant)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan in this specimen; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

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

Identified May 13, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan in this specimen; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to its sharp edges; used as flint in strike-a-lights; currently used in construction aggregate and as a semi-precious gemstone for jewelry when colorful.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which led to its historically vital use in flintlock firearms and starting fires.

Field identification & locations

Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found in riverbeds or eroding out of limestone cliffs.