sedimentary

Chert (Green variety)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Greenish-gray (due to chlorite or celadonite inclusions); Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Greenish-gray (due to chlorite or celadonite inclusions)
Luster: Dull to waxy

Identified March 26, 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 from hydrothermal fluids in marine environments. Often found in nodules or bedded layers within limestone or shale.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a semi-precious stone for lapidary work.

Geological facts

Chert is so hard it can scratch steel and was used by ancient humans to create sparks for fire. The green variety is often called 'green jasper' if it is opaque and highly pigmented.

Field identification & locations

Identify in the field by its characteristic 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. It is common in mountainous regions and riverbeds across North America and Europe.

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)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary