sedimentary

Chert / Flint Nodules

Chert (Cryptocrystalline variety of Quartz, SiO2)

AI-generated identification · may be incorrect

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

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

Identified April 26, 2026More sedimentary →

Explore Chert / Flint Nodules in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

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

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. These nodules often grow within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads/knives) due to sharp edges when fractured. Modern uses include road surfacing, jewelry (when colorful), and fire-starting strikers.

Geological facts

Chert was one of the most important raw materials for early humans. Because it breaks with a conchoidal fracture, it creates edges Sharper than a surgical scalpel.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture pattern. Often found as rounded nodules or layers in limestone outcrops.