sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Rusty brown, tan, or grey due to iron impurities; Luster: Dull to waxy; Structure: Microcrystalline with conchoidal (shell-like) fracture; Cleavage: None.

Hardness: 7 on Mohs scale
Color: Rusty brown, tan, or grey due to iron impurities
Luster: Dull to waxy

Identified April 12, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Rusty brown, tan, or grey due to iron impurities; Luster: Dull to waxy; Structure: Microcrystalline with conchoidal (shell-like) fracture; Cleavage: None.

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads). Modernly used as construction aggregate, road base, and occasionally for rock tumbling/landscaping.

Geological facts

Chert is extremely durable and chemically resistant. When it contains high amounts of iron oxide, it takes on the characteristic brownish-red 'jasper-like' appearance seen in this specimen.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved fracture surfaces. Commonly found in riverbeds, gravel pits, and glacial till.