sedimentary

Chert (Iron-stained)

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, ochre (due to iron oxidation), gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Fracture: Conchoidal; Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, ochre (due to iron oxidation), gray
Luster: Waxy to dull

Identified May 29, 2026More sedimentary →

Explore Chert (Iron-stained) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, ochre (due to iron oxidation), gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Fracture: Conchoidal; Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organisms (like radiolarians or diatoms) or chemical precipitation in marine or groundwater environments. This specimen shows significant weathering and iron oxide staining from long-term exposure to water and air.

Uses & applications

Historically used for stone tools and weapons (flint-knapping); currently used as a common construction aggregate, landscaping stone, and in some decorative lapidary work.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early human civilizations to create sharp edges for hunting and survival.

Field identification & locations

Identify in the field by its very hard, smooth texture, waxy luster, and conchoidal (shell-like) fractures. It will not react with acid. Commonly found in limestone or chalk beds as nodules or layers.