Chert (and Flint variant)

Physical Properties

Hardness: 7 (Mohs scale), Color: Dark grey, black, or mottled white, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Often found in nodules within limestone or chalk beds.

Uses & Applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used as road aggregate, in glass making, and as a component in ceramics. Sometimes used in jewelry as 'Jasper' or 'Flint'.

Geological Facts

Chert was one of the first materials harvested by early humans. Because of its hardness and conchoidal fracture, it can create edges sharper than a steel scalpel. Darker varieties are typically referred to as Flint.

Field Identification & Locations

Identify by its 'shell-like' conchoidal fracture patterns and that it is hard enough to scratch glass. It often has a white waxy outer 'rind' if found within limestone. Common in riverbeds and limestone outcrops.

Identified on: 4/25/2026

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