sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: White to tan/light gray with earthy staining; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 on Mohs scale
Color: White to tan/light gray with earthy staining
Luster: Dull to waxy

Identified June 15, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: White to tan/light gray with earthy staining; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed via the accumulation of silica-rich organic remains (diatoms, radiolarians) or chemical precipitation in marine environments during various geological eras from Precambrian to Cenozoic.

Uses & applications

Used historically for stone tools and weapons due to sharp edges; currently used for road ballast, construction aggregate, and occasionally in lapidary work.

Geological facts

Chert is so hard it can scratch steel and was famously used to produce sparks for flintlock firearms; it is chemically identical to quartz but contains microscopic crystals.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture and high hardness - it will easily scratch glass. Commonly found in limestone and dolomite beds as nodules or layers.