sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7.0 (Mohs scale), Color: White, tan, and reddish-brown (from iron oxidation), Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Hardness: 7

Identified February 21, 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 by chemical precipitation from groundwater within limestone or chalk beds. This specimen displays secondary iron staining and weathering.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp edges. Modern use includes landscaping, concrete aggregate, and occasional lapidary work for tumbled stones.

Geological facts

Chert is so durable that it often remains as 'river gravel' long after the surrounding limestone bedrock has eroded away. It was one of the most important minerals for prehistoric humans because it sparks when struck against steel or pyrite.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in stream beds, gravel pits, and as nodules in sedimentary outcrops.