sedimentary

Chert (Green Fossilized Algae or Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Olive green to brownish-green, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline (Trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Hardness: 6

Identified July 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains, such as diatoms or radiolarians, or through chemical precipitation in sedimentary environments. Green varieties often contain chlorite inclusions or aged organic matter.

Uses & applications

Historically used for stone tools due to its sharp conchoidal fracture. Modern uses include jewelry (as jasper), landscaping, and as a collector's specimen.

Geological facts

Chert is so durable that it survives long after surrounding limestone or chalk has eroded away. Green chert can sometimes resemble nephrite jade but is distinguished by its higher hardness and more brittle nature.

Field identification & locations

Look for a smooth, waxy surface and distinct shell-like (conchoidal) fractures. It is commonly found in stream beds or within sedimentary rock layers like limestone. It will scratch glass easily.

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