sedimentary

Chert (and Limestone)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or white with waxy/dull luster; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Hardness: 7 on Mohs scale
Color: Gray, tan, or white with waxy/dull luster

Identified March 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments during various geological eras (often Paleozoic/Mesozoic). It frequently occurs as nodules within limestone beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modern uses include road construction aggregate, abrasives, and as a component in certain ceramics.

Geological facts

Chert and its variety Flint played a vital role in human evolution as the primary material for the Stone Age toolkits. It can spark when struck against steel, making it useful for early fire-starting and flintlock firearms.

Field identification & locations

Identify in the field by its hardness (will scratch glass) and its smooth, shell-like (conchoidal) breakage patterns. Often found in layered sedimentary outcrops or as rounded river cobbles in limestone-heavy regions.