sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, brown, and cream banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, and cream banding
Luster: Waxy to dull

Identified June 11, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, and cream banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily through the chemical precipitation of silica-rich fluids within sedimentary environments, often replacing carbonate material or accumulating as nodules in limestone/chalk. This specimen shows distinct banding indicative of cyclic deposition.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modernly used as road gravel, in concrete aggregate, and sometimes as a semi-precious gemstone in lapidary work.

Geological facts

Chert is so hard it can strike sparks against steel, which made it the primary material for flintlock firearms. It is chemically identical to quartz but has a much finer grain structure.

Field identification & locations

Identify in the field by its smooth, waxy feel, conchoidal (shell-like) fracture patterns, and its ability to scratch glass. Commonly found in stream beds or weathered out of limestone cliffs.