sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Tan, beige, or yellowish-brown due to iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Tan, beige, or yellowish-brown due to iron oxide staining
Luster: Waxy to dull

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in sedimentary environments. Iron staining occurs as groundwater rich in iron minerals permeates the porous exterior over geological time.

Uses & applications

Historically used for stone tools and arrowheads because of its sharp conchoidal edges; currently used in construction aggregate, road surfacing, and as landscaping stone.

Geological facts

Chert is so chemically stable that it often remains in the soil long after the surrounding limestone or chalk has weathered away. It was one of the most vital materials for prehistoric humans globally.

Field identification & locations

Identify by its 'waxy' texture when broken and its ability to scratch glass. It will show smooth, shell-like (conchoidal) curves on broken surfaces. Very common in riverbeds and limestone outcrops throughout the United States and Europe.

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