sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 (Mohs scale), Color: light grey to white, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: light grey to white, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8

Formation & geological history

Formed by the accumulation of siliceous remains such as radiolarian or diatom skeletons, or by inorganic precipitation of silica from seawater. Often found in nodules within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Currently used in road construction, as an abrasive, and sometimes as a decorative stone.

Geological facts

Chert and its variety, flint, were among the most important materials for early human technology. When struck against steel, it can create sparks used for starting fires.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its smooth conchoidal (shell-like) fracture surfaces, and its dense, non-porous appearance. Common in limestone outcrops.