sedimentary

Chert (often called Flint or Jasper based on color)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, yellow-brown, or reddish (likely due to iron oxide staining); Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Luster: Waxy to dull

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or by the chemical precipitation of silica in groundwater within limestone or chalk beds. Often Paleozoic to Mesozoic in age.

Uses & applications

Historically used for stone tools (knapping) due to sharp edges; currently used for road surfacing, gravel, and occasionally as semi-precious gemstones (Jasper) for jewelry.

Geological facts

Chert was one of the most important minerals for early humans, used to create spearheads and arrowheads. It can produce sparks when struck against steel, leading to its use in flintlock firearms.

Field identification & locations

Identify in the field by its very smooth, glass-like fracture (conchoidal) and its ability to scratch glass. It is commonly found in nodules within limestone or as river-worn pebbles. Common in the Midwest and Southern US.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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