Chert (Flint) Nodule

Physical Properties

Hardness: 7 on Mohs scale; Color: Variable (white, tan, yellow, gray); Luster: Dully waxy to vitreous when fresh; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & Geological History

Formed through the replacement of limestone or chalk by silica-rich fluids, or as primary chemical precipitates in marine environments. Often found in Cretaceous chalk deposits.

Uses & Applications

Historically used for stone tools and strike-a-lights; currently used as decorative gravel, in road construction, and for primitive fire-starting tools.

Geological Facts

Chert nodules are often found in distinct layers within limestone beds. High-purity dark gray/black varieties are specifically called 'flint' and were essential to prehistoric human technology.

Field Identification & Locations

Identify in the field by its characteristic smooth, curved (conchoidal) fractures and its ability to scratch glass. Look for rounded, waxy-textured lumps in chalk or limestone outcrops.

Identified on: 4/27/2026

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