sedimentary

Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Tan, brown, and yellowish-grey with earthy weathering. Luster: Dull to waxy when fresh. Crystal structure: Cryptocrystalline (microscopic grains). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 6
Color: Tan, brown, and yellowish-grey with earthy weathering
Luster: Dull to waxy when fresh

Identified April 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (such as diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary beds. This specimen reflects water-worn rounding from a river or beach environment.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used in construction aggregate and sometimes as lapidary material for tumbling.

Geological facts

Chert is so durable that it often survives long after the surrounding softer limestone or chalk has eroded away. It is one of the most common materials used by prehistoric humans for lithic technology.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces if chipped. It often feels denser and smoother than surrounding sandstone or limestone.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

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Sandstone (with man-made markings)

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