sedimentary

Chert (specifically Flint or Dark Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Dark brown to black. Luster: Dull to waxy. Crystal Structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Dark brown to black
Luster: Dull to waxy

Identified April 11, 2026More sedimentary →

Explore Chert (specifically Flint or Dark Chert) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Dark brown to black. Luster: Dull to waxy. Crystal Structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary rock layers, typically limestone or chalk.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Industrially used as an abrasive or in construction aggregate. Highly valued by flint-knappers for making arrowheads.

Geological facts

Chert was one of the most important materials for early humans because of its conchoidal fracture, which produces edges sharper than a steel scalpel. Darker varieties often get their color from organic carbon impurities.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture patterns and the fact it can scratch glass. It is often found as nodules in limestone or as stream-worn pebbles.