sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Dark brown to grey with white veining; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal; Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Dark brown to grey with white veining
Luster: Waxy to dull

Identified July 17, 2026More sedimentary →

Explore Chert (Nodule) 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 on Mohs scale; Color: Dark brown to grey with white veining; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Fracture: Conchoidal; Specific gravity: 2.65.

Formation & geological history

Formed by the accumulation of microcrystalline silica, typically in marine environments where silica-rich fluids replace carbonate material or precipitate from dissolved silica-rich organisms. Commonly found in limestone or chalk beds.

Uses & applications

Historically used for stone tools (flintknapping); currently used as an abrasive, in landscaping, and as a component in construction aggregate.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans because of its ability to produce sharp edges when fractured.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness, and distinctive shell-like (conchoidal) fractures. Common in sedimentary basins worldwide, especially where ancient sea beds are exposed.