sedimentary

Chert (Nodular)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale), Color: tan, grey, brown with occasional dark inclusions, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Hardness: 6

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater filling pores in limestone or chalk, or from the accumulation of silica-rich microfossils. Often found in Phanerozoic Era sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads/knives) due to sharp edges; currently used for road aggregate, gravel, and occasionally as a source of high-purity silica for manufacturing.

Geological facts

Chert is so hard it can easily scratch glass. It was one of the most vital materials for early humans because its conchoidal fracture allows it to be shaped into razor-sharp edges.

Field identification & locations

Identify by its waxy texture and 'shell-like' curved fractures (conchoidal). It is common in limestone outcrops and river beds. Collectors look for pieces with unique banding or fossils trapped inside.