sedimentary

Chert (often called Flint or Jasper)

Chert (Microcrystalline or Cryptocrystalline Silica, SiO2)

Hardness: 7 on the Mohs scale; Color: Tan, beige, and reddish-brown marbling; Luster: Dull to waxy; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.

Hardness: 7 on the Mohs scale
Color: Tan, beige, and reddish-brown marbling
Luster: Dull to waxy

Identified March 20, 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 chemical precipitation in marine environments; primarily found in limestone or chalk beds. Most specimens date from various eras ranging from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (knapping for arrowheads) and fire-starting (flint). Currently used as an abrasive, in road construction, and as semi-precious gemstones for jewelry (Jasper variety).

Geological facts

Because it breaks with a conchoidal fracture (smooth, curved surfaces), it was the most important material for early human tool-making. It is so chemically stable that it often preserves microfossils exceptionally well.

Field identification & locations

Identify in the field by its high hardness (cannot be scratched by a steel nail), waxy texture, and sharp petal-like edges when broken. Frequently found in stream beds or within sedimentary rock outcrops.

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