sedimentary
Chert (Flint Nodule)
Microcrystalline or cryptocrystalline quartz (SiO2)
Hardness: 7 (Mohs), Color: Tan to brown with grey patches, Luster: Waxy to dull, Crystal structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Tan to brown with grey patches, Luster: Waxy to dull, Crystal structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of organisms or chemical precipitation within limestone or chalk beds. Commonly associated with Cretaceous or Jurassic chalk deposits.
Uses & applications
Historical use for tool-making (arrowheads, knives), industrial grinding media, road aggregate, and used in fire-making due to its ability to create sparks.
Geological facts
Flint was the primary material for the Stone Age tools that allowed early humans to hunt and process food. It produces a very sharp, glass-like edge when fractured.
Field identification & locations
Identify in the field by its waxy texture, shell-like (conchoidal) fracture patterns, and its ability to scratch glass. Its rounded but irregular shape suggests it is a weathered nodule from a chalk matrix.
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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