sedimentary

Chert (and Quartz Gravel)

Chert (Cryptocrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray (iron-stained); Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none (conchoidal fracture); SG: 2.65

Hardness: 7 on Mohs scale
Color: typically tan, brown, or gray (iron-stained)
Luster: waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray (iron-stained); Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none (conchoidal fracture); SG: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater. These specimens usually represent river-worn stones found in alluvial deposits or glacial till.

Uses & applications

Used primarily as road base, construction aggregate, and in landscaping. Historically used for making stone tools (arrowheads) due to its sharp edges when broken.

Geological facts

Chert is so hard it can create sparks when struck against steel. It is one of the most common rocks found in riverbeds worldwide because it is highly resistant to chemical and physical weathering.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fractures. It will not be scratched by a steel knife. Very common in limestone-rich regions and gravel pits.