sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Black, brown, and yellowish-tan; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Black, brown, and yellowish-tan
Luster: Waxy to vitreous

Identified June 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Black, brown, and yellowish-tan; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily from the accumulation of silica-rich microfossils or via chemical precipitation within limestone or chalk beds. This specimen likely originated as a nodule in sedimentary strata.

Uses & applications

Historically used for stone tools and starting fires (flint and steel). Modern uses include high-end road aggregate, semi-precious jewelry (when colorful/patterned), and gravel.

Geological facts

Chert has been used by humans for over two million years to make arrowheads and scrapers because it breaks into very sharp edges. It is chemically very resistant to weathering.

Field identification & locations

Identify by its smooth, waxy surface and shell-like (conchoidal) fracture pattern. To distinguish from glass, check for its ability to scratch steel and its characteristic duller luster. Common in riverbeds and limestone outcrops.