sedimentary

Chert (Flint/Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, reddish-brown with white crust (cortex); Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Breakage: Conchoidal fracture.

Hardness: 6
Color: Brown, tan, reddish-brown with white crust (cortex)
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, reddish-brown with white crust (cortex); Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Breakage: Conchoidal fracture.

Formation & geological history

Formed as nodules or layers in sedimentary rocks (like limestone or chalk) through the accumulation of silica-rich organic remains or chemical precipitation. These specimens can range from millions to hundreds of millions of years old.

Uses & applications

Historically used for stone tools and weapons (arrowheads) due to its sharp edges; modern uses include road surfacing, jewelry (when colorful/polished), and fire-starting kits.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which is why it was essential for flintlock firearms and early survival gear.

Field identification & locations

Identify in the field by its smooth, shell-like fracture surfaces and extreme hardness. Look for nodules with a white, chalky outer weathering rind (cortex) in limestone outcrops or riverbeds.