sedimentary

Chert (and Flint)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 7 on Mohs scale; Color: Tan, beige, white, and gray; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (hexagonal sub-microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65.

Hardness: 7 on Mohs scale
Color: Tan, beige, white, and gray
Luster: Waxy to dull

Identified April 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds. Formed throughout geological time from Precambrian to Cenozoic.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, architectural stone, or polished for lapidary jewelry.

Geological facts

Because chert breaks with a conchoidal fracture (smooth, curved surfaces), it was the primary material for prehistoric survival technologies. Variants like Jasper and Agate are prized for their colors.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and steel), waxy texture, and distinctive shell-like fracture pattern. Often found in riverbeds or eroding out of limestone cliffs.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

Arenite (primarily SiO2)

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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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