sedimentary

Chert (Field-collected specimen)

Chert (Crystalline Silica, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grayish-tan to brown; Luster: Dull to waxy; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grayish-tan to brown
Luster: Dull to waxy

Identified April 1, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grayish-tan to brown; Luster: Dull to waxy; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms or the chemical precipitation of silica in sedimentary environments. Common in limestone and dolostone formations spanning from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative stone in landscaping, road aggregate, and by hobbyist flintknappers.

Geological facts

Chert is so hard it can easily scratch glass and will spark when struck against steel. It is one of the most durable rocks and often survives weathering long after the surrounding limestone has eroded.

Field identification & locations

Identify in the field by its extreme hardness, smooth conchoidal fracture (shell-like curves when broken), and lack of reactivity to acid. Common in riverbeds and as nodules in limestone outcrops.