sedimentary

Chert (Green Chert/Jasper)

Chert (primarily Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Dull olive green to dark gray-green; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.6-2.65.

Hardness: 7 on Mohs scale
Color: Dull olive green to dark gray-green
Luster: Waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) on the ocean floor, followed by replacement of other minerals or direct precipitation from water into nodules or beds within sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges when broken; currently used in decorative landscaping, lapidary as tumbled stones, and as a component in certain industrial abrasives.

Geological facts

Green chert is often associated with the Franciscan Complex in California or other ancient seafloor deposits. It is so tough that it can spark when struck with steel, a property it shares with flint.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its smooth waxy feel, and its curved 'seashell-like' fractures. Commonly found in riverbeds or coastal cliffs where sedimentary formations are eroding.

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