sedimentary

Chert (often called Flint or Jasper)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray with reddish oxidation; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none (fractures conchoidally); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: typically tan, brown, or gray with reddish oxidation
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 radiolaria or diatoms) or by chemical precipitation in limestone or chalk beds. Often Cretaceous to Paleozoic in age.

Uses & applications

Used historically for stone tools and arrowheads; currently used as road aggregate, in glassmaking (if high purity), and polished as semi-precious gemstones for jewelry (jasper variants).

Geological facts

Because it breaks with a conchoidal fracture (smooth, curved surfaces), it can produce edges sharper than a surgical scalpel. It was one of the most vital survival resources for prehistoric humans.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and waxy texture. To test, look for rounded, shell-like fracture marks. Common in limestone exposures and riverbeds worldwide.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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