sedimentary

Chert (Green variety)

Microcrystalline Opaline/Quartz (SiO2)

Hardness: 6.5–7 (Mohs); Color: Dark green to dull grey-green; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Color: Dark green to dull grey-green
Luster: Waxy to dull

Identified April 2, 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 by chemical precipitation from silica-rich fluids in ocean basins. These specimens can range from Precambrian to Cenozoic in age.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Modernly used as landscaping stone, river rock, and occasionally as a semi-precious gemstone when it exhibits attractive patterns (Jasper).

Geological facts

Chert was one of the most important minerals for early humans because its sharp edges when broken were ideal for hunting and skinning. Green chert often gets its color from trace amounts of chlorite or iron.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Common in riverbeds or coastal areas where it has been smoothed by water. Found globally in limestone and chalk formations.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

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Sandstone (with man-made markings)

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