sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Variegated brown, grey, and tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Variegated brown, grey, and tan
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Variegated brown, grey, and tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the chemical precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of marine organisms. Commonly found in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; currently used for decorative gravel, abrasives, and as a collector's specimen.

Geological facts

Chert is extremely durable and chemically stable, often surviving millions of years of erosion. Some chert nodules contain microfossils visible only under magnification.

Field identification & locations

Identify in the field by its waxy texture and conchoidal (shell-like) fracture pattern. It will easily scratch glass. Commonly found in riverbeds or within sedimentary rock outcrops.