sedimentary

Chert (Flint)

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Brown, gray, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Brown, gray, or tan
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, gray, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich microfossils or via chemical precipitation from silica-rich groundwater within limestone or chalk beds. Commonly found in Mesozoic or Paleozoic sedimentary layers.

Uses & applications

Historically used for making stone tools and starting fires (striking steel). Modern uses include road surfacing, decorative landscaping, and occasionally as semi-precious gemstones (jaspers).

Geological facts

Chert was one of the most vital materials for early humans due to its ability to break into razor-sharp edges. Flint is a specific dark variety of chert often found in chalk deposits.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and high hardness (it will scratch glass). Often found as nodules within limestone outcrops or as pebbles in stream beds.