sedimentary

Chert (Gravel Bit)

Microcrystalline silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Brown/Opaque; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Brown/Opaque
Luster: Waxy to dull

Identified March 15, 2026More sedimentary →

Explore Chert (Gravel Bit) 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: Brown/Opaque; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of microorganisms (like radiolaria) in marine environments. This specimen appears to be a weathered fragment of common river or construction gravel.

Uses & applications

Common varieties are used in road construction, concrete aggregate, and landscaping. Historically, varieties like flint were used to make sharp tools and arrowheads.

Geological facts

Chert is so hard it can scratch steel and glass. It is chemically identical to quartz but has a much finer, microscopic grain structure that makes it appear opaque rather than translucent.

Field identification & locations

Identify in the field by its hardness and its tendency to break with smooth, curved 'shell-like' surfaces (conchoidal fracture). It is found globally in sedimentary rock layers or as loose gravel in riverbeds.