sedimentary

Chert (and Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Typically grey, tan, or white with distinct banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Typically grey, tan, or white with distinct banding
Luster: Waxy to dull

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or through the chemical precipitation of silica in groundwater. Can be found in rocks from the Precambrian era to the present.

Uses & applications

Used historically for stone tools (arrowheads, scrapers) due to its sharp edges; used today as road base, in concrete, and as high-quality flint for fire-starting. Banded varieties are used as ornamental stones.

Geological facts

Chert is so hard it can scratch steel. It was the primary material for the Stone Age technology. The 'flint' used in flintlock firearms is a variety of dark-colored chert.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture patterns and ability to scratch glass. It is commonly found as nodules in limestone or as distinct bedded layers. Collector tips: look for smooth, waxy surfaces and sharp edges.