sedimentary

Chert (specifically Gray Chert/Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale. Color: Gray, tan, and creamy white. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, and creamy white
Luster: Waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: Gray, tan, and creamy white. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and strike-a-lights. Industrially used as an abrasive and in glass making. Common in landscaping gravel.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges. It is chemically identical to quartz and amethyst but has a different internal structure.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) breakage patterns. Found globally, especially in sedimentary basins.