sedimentary

Chert / Flint

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, and dark grey
Luster: Waxy to dull

Identified March 23, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater or as a biological process where silica-rich organisms (like radiolarians) settle on the seafloor and undergo diagenesis. Found in many geological ages, particularly within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges. Currently used in road construction, as architectural stone, or for fire-starting in flintlock mechanisms.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the first materials traded over long distances by prehistoric humans for its tool-making properties.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its ability to spark when struck against steel. Commonly found in stream beds or eroding out of limestone outcrops.