sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale. Color: Grayish-brown with waxy to dull luster. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 7 Mohs scale
Color: Grayish-brown with waxy to dull luster

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale. Color: Grayish-brown with waxy to dull luster. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Formation & geological history

Formed in marine sedimentary environments through the precipitation of silica from seawater or the accumulation of siliceous skeletal remains (like radiolaria) within limestone or chalk beds.

Uses & applications

Historically used for stone tools (flint knapping). Today used as laboratory mortar and pestles, road material, or as decorative river rock.

Geological facts

Chert is so durable that it often remains as pebbles in stream beds long after the surrounding limestone has eroded away. Varieties include flint, jasper, and agate.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy luster when freshly broken, and smooth, rounded water-worn exterior often found in riverbeds.