sedimentary

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Variable (tan, grey, red-brown due to iron impurities); Luster: Waxy to dull; Structure: Non-crystalline visible mass; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Variable (tan, grey, red-brown due to iron impurities)
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 diatoms or radiolarians) or through the chemical replacement of limestone/dolomite by silica-rich fluids. Can be found in outcrops ranging from Precambrian to Cenozoic eras.

Uses & applications

Used historically for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as a semi-precious stone in jewelry or lapidary arts when colorful (jasper).

Geological facts

Because of its conchoidal fracture, it breaks into extremely sharp edges, making it the primary material for prehistoric arrowheads and spear points. It was also essential for flintlock firearms.

Field identification & locations

Identify by its extreme hardness (will scratch glass or steel) and shell-like (conchoidal) fracture patterns. Frequently found as nodules in limestone beds or as rounded river cobbles.

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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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