sedimentary

Chert (specifically Pink Chert or Jasperized Chert)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 7 (Mohs scale); Color: Pink, tan, and grey with iron oxide staining; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.

Hardness: 7 (Mohs scale)
Color: Pink, tan, and grey with iron oxide staining
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from hydrothermal fluids in limestone or volcanic environments. Often dates from the Paleozoic to Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for road aggregate, landscaping, flint-knapping enthusiasts, and occasionally lapidary cabochons.

Geological facts

Chert is so hard it can strike sparks against steel, which is why varieties like flint were essential for early firearms. It is chemically very stable and resistant to weathering.

Field identification & locations

Identify in the field by its distinct conchoidal (shell-like) fracture patterns and ability to scratch glass. Commonly found in nodular form within limestone beds or as rounded river cobbles in gravel deposits.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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