sedimentary

Chert (Cherty Limestone / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically gray, tan, or brown with waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: typically gray, tan, or brown with waxy luster

Identified March 22, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically gray, tan, or brown with waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from seawater or the replacement of carbonate minerals (like limestone) by silica-rich fluids. Often found as nodules or layers in marine sedimentary rocks dating from the Precambrian to Holocene.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp fracture edges. Industrially used as decorative stone, road ballast, or in the manufacturing of glass and ceramics.

Geological facts

Chert is so hard it can scratch steel and was used for centuries as a 'strike-a-light' to create sparks for fire. Darker varieties are commonly known as Flint.

Field identification & locations

Identify in the field by its characteristic 'seashell-like' (conchoidal) fracture, sharp edges, and ability to scratch glass. It often feels smoother or waxier than the limestone it may be embedded in.