sedimentary

Chert (Red Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brick red to brownish-red due to iron inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.58-2.91

Hardness: 6
Color: Brick red to brownish-red due to iron inclusions
Luster: Dull to waxy

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brick red to brownish-red due to iron inclusions; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Gravity: 2.58-2.91

Formation & geological history

Formed through the accumulation of silica-rich microfossils like radiolaria or diatoms on the seafloor, later replaced by silica through diagenesis. Red varieties are common in Paleozoic to Mesozoic sedimentary sequences.

Uses & applications

Used as a gemstone for jewelry (cabochons), lapidary art, and historically for stone tools due to its sharp edges when broken. Also used in construction as an abrasive or aggregate.

Geological facts

Red chert is often associated with iron-rich environments. Ancient civilizations used Jasper for seals, amulets, and spearheads because of its hardness and predictable fracture pattern.

Field identification & locations

Identify by its 'flint-like' smooth, curved fracture surfaces and its inability to be scratched by a steel knife. Commonly found in riverbeds, glacial till, and coastal cliffs.