Sedimentary

Chert (and Chert-based Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale; Color: typically tan, grey, cream, or brownish with darker dendritic veins; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on the Mohs scale
Luster: waxy to dull

Identified March 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Can appear in sedimentary beds or as nodules within limestone or chalk.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Modern uses include decorative gravel, tumbled gemstones for jewelry, and lapidary art.

Geological facts

Because of its high silica content and density, Chert has been used by humans for over a million years. It is chemically identical to flint, though 'flint' is a term usually reserved for chert found in chalk or marly limestone.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), smooth waxy feel, and its tendency to break into sharp, curved 'shell-like' edges. Common in river beds and sedimentary outcrops worldwide.

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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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