sedimentary

Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Grey to brownish-tan with banded weathering; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Grey to brownish-tan with banded weathering
Luster: Waxy to dull

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a chemical precipitate or byproduct of biological activity (like diatoms or radiolarians) in deep-sea environments or as replacement nodules in limestone. Most specimens range from hundreds of millions to billions of years old.

Uses & applications

Historically used for stone tools and fire-starting due to its hardness and sharp edges. Today used as gemstones, in jewelry, or as industrial abrasives.

Geological facts

Chert has been used by humans for over 2 million years to create spear points, arrowheads, and knives. It produces sparks when struck against steel, which led to its use in flintlock firearms.

Field identification & locations

Look for a smooth, waxy texture and conchoidal (shell-like) fracture patterns. It is very hard and will scratch glass. Common in riverbeds, glacial tills, and within limestone outcrops worldwide.

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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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