sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: dull gray to brown, Luster: waxy to dull, Structure: microcrystalline, Cleavage: none (conchoidal fracture)

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: dull gray to brown, Luster: waxy to dull, Structure: microcrystalline, Cleavage: none (conchoidal fracture)

Formed as nodules in limestone or chalk through the replacement of calcium carbonate by silica-rich fluids. Often dates from the Cretaceous period.

Historically used for stone tools and starting fires (striking steel). Modernly used in construction aggregate and road surfacing.

Chert was one of the most important materials for early human technology. When broken, it creates edges sharper than a steel scalpel.

Identify by its extremely smooth, shell-like fracture surfaces and ability to scratch glass. Found globally in sedimentary basins.

Sandstone or Siltstone

Arenite (if sandstone)

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

Shale or Slaty Mudstone

Argillaceous sedimentary rock

Sandstone

Arenite (primarily SiO2)