sedimentary

Chert (Red/Pink variety)

Microcrystalline quartz (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Reddish-brown to pink due to iron oxide impurities, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7

Hardness: 6

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians) or inorganic precipitation from groundwater in sedimentary environments. Can date from various geological periods, often Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and arrowheads because it fractures like glass. Modernly used in landscaping, as an abrasive, and sometimes in jewelry (as Jasper) when highly polished.

Geological facts

Chert is so hard it can spark when struck against steel. Prehistoric humans traded high-quality chert over hundreds of miles to create specialized tools.

Field identification & locations

Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass easily. Commonly found as nodules in limestone or as distinct bedded layers.

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Sandstone or Siltstone

Arenite (if sandstone)

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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