sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, brown, with dark streaks; Luster: Waxy to vitreous; Crystal Structure: Microscopic trigonal/hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Tan, brown, with dark streaks
Luster: Waxy to vitreous

Identified February 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. Often found in nodules or bedded layers within limestone or shale deposits, typically ranging from Precambrian to Cenozoic ages.

Uses & applications

Historically used for stone tools (arrowheads/knives) due to sharp edges; currently used for road ballast, jewelry (cabochons), and as a gemstone for lapidary work.

Geological facts

Chert is so hard it can scratch steel and was used for centuries to start fires when struck against iron (flint and steel). It is a primary material used by prehistoric humans for lithic technology.

Field identification & locations

Identify in the field by its waxy texture, smooth conchoidal (shell-like) fractures, and its ability to scratch glass. Commonly found in riverbeds or eroded out of limestone outcrops. Collectors should look for unique banding or color patterns.

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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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