sedimentary

Chert (Flint)

Microcrystalline quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, tan, or gray
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments such as limestone or chalk beds. It can date from the Precambrian to recent times.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Today used as a decorative stone, road gravel, and occasionally for lapidary work or semi-precious jewelry.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for hunting and scraping tools.

Field identification & locations

Identify in the field by its smooth, waxy surface and its ability to scratch glass. Look for rounded nodules often encased in a lighter-colored 'cortex' or chalky outer layer. Common in riverbeds and limestone outcrops.