sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Dark grey to black with tan/brown interior; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Dark grey to black with tan/brown interior
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Dark grey to black with tan/brown interior; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich fluids in limestone or chalk beds, often replacing organic materials or filling voids. These nodules are common in sedimentary basins ranging from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used for road aggregate, landscaping, and as a collector's specimen.

Geological facts

Chert nodules often contain microscopic fossils. When high-quality and dark, it is frequently referred to as flint, which was essential for starting fires in colonial times.

Field identification & locations

Identify by its smooth, waxy texture and shell-like (conchoidal) fracture when broken. Frequently found in riverbeds or eroding out of limestone cliffs.