sedimentary

Chert (Jasper/Flint variety)

Silicon dioxide (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Multi-colored with browns, reds, and dull greens; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.

Hardness: 6
Color: Multi-colored with browns, reds, and dull greens
Luster: Waxy to vitreous

Identified April 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich fluids in sedimentary environments or through the replacement of limestone/chalk by silica. It often occurs as nodules or massive beds originating from prehistoric marine environments.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Today used for lapidary work, decorative landscaping, and as a raw material for silicon production.

Geological facts

Because it breaks into extremely sharp edges, chert was one of the first materials humans used to build technology. It is chemically identical to quartz but has a different micro-structure.

Field identification & locations

Identify in the field by its smooth, waxy surface and its distinct shell-like (conchoidal) fracture pattern when broken. It is commonly found in riverbeds, glacial till, and embedded within limestone formations.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary