sedimentary

Chert (Flint/Jasper variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, or grayish-yellow
Luster: Waxy to dull

Identified March 8, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-yellow; 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 the accumulation of siliceous skeletal remains (diatoms/radiolarians) in marine environments. These specimens often originate in limestone or chalk beds from various geological eras, including the Cretaceous.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in road construction as aggregate, as a component in certain ceramics, and as decorative gravel.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a surgical scalpel. It is also famous for its use in fire-starting as 'flint' when struck against steel.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its characteristic shell-like (conchoidal) fracture pattern when broken. It is commonly found in riverbeds, agricultural fields, or eroding out of limestone outcrops worldwide.