sedimentary

Chert (Field-collected variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Pinkish-tan to light grey with iron oxide staining; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Pinkish-tan to light grey with iron oxide staining
Luster: Waxy to dull

Identified March 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through chemical precipitation or by the replacement of other materials by silica. Often found in nodules or bedded deposits within limestone or chalk; geological age spans from the Precambrian to present day.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used in road construction as aggregate, lapidary cabochons, and as fire-starters in survival kits.

Geological facts

Because it breaks with a conchoidal fracture, it was the primary material for the Stone Age tool industry alongside flint. Some colorful varieties are known localized as 'Jasper'.

Field identification & locations

Identify in the field by its hardness (will scratch glass and steel), waxy texture when freshly broken, and smooth, curved fracture surfaces. Found worldwide in sedimentary basins and riverbeds.

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

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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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