sedimentary

Chert (Quartz Variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, grey
Luster: Waxy to dull

Identified May 27, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as nodules or beds in sedimentary rock through the accumulation of siliceous remains of organisms like diatoms and radiolarians, or through chemical precipitation in hydrothermal veins.

Uses & applications

Historically used for making sharp tools and arrowheads. Currently used in road construction, as an abrasive, and sometimes as an decorative garden stone.

Geological facts

Chert is so hard it can scratch glass and steel. Different varieties of chert include flint, jasper, and agate. It is highly resistant to chemical weathering.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to spark when struck against steel. Often found in limestone or chalk deposits and as water-worn pebbles in stream beds.