sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: brown to dark grey; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: brown to dark grey
Luster: waxy to dull

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: brown to dark grey; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the precipitation of silica from groundwater within limestone or chalk beds, or from the accumulation of siliceous organisms on the ocean floor.

Uses & applications

Historically used for making stone tools (flint); currently used in road construction, as a decorative landscape stone, and as rough material for lapidary tumbling.

Geological facts

Chert is so hard it can create sparks when struck against steel. It was one of the most important minerals for early humans to create sharp cutting tools and fire-starters.

Field identification & locations

Identify in the field by its smooth, waxy texture and sharp, shell-like (conchoidal) edges when broken. It will often scratch glass and is found in sedimentary basins.