sedimentary

Chert Breccia (with Iron Staining)

Microcrystalline Quartz (SiO2) with iron oxides (Limonite/Goethite)

Hardness: 7 (Mohs scale). Color: Tan, white, grey with reddish-brown staining. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, white, grey with reddish-brown staining
Luster: Dull to waxy

Identified June 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich fluids or shells in marine or groundwater environments, followed by fragmentation (brecciation) and re-cementation. The reddish-brown patches are caused by the oxidation of iron-bearing minerals.

Uses & applications

Primarily used as construction aggregate or road base. Historically used for stone tools due to its sharp edges; occasionally used in lapidary for tumbled stones if colorful colors are present.

Geological facts

Chert is so durable that it often remains behind as 'residual lag' long after the surrounding limestone or dolomite bedrock has weathered away. It is one of the most common materials for arrowheads.

Field identification & locations

Identify by its hardness (will scratch glass), fine-grained texture, and conchoidal (clamshell-like) fractures. It is commonly found in gravel pits, creek beds, and limestone outcrops.

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