sedimentary

Flint / Chert Pebble

Cryptocrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale; Color: Dark grey to white mottled pattern; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.60 to 2.65

Hardness: 7 on the Mohs scale
Color: Dark grey to white mottled pattern
Luster: Waxy to vitreous

Identified August 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of calcium carbonate by silica-rich solutions in marine limestone or chalk environments, typically during the Cretaceous period or earlier.

Uses & applications

Historically used for making stone tools, arrowheads, and firearm ignition (flintlock). Today mainly collected as beach pebbles or used in landscaping and decorative gravel.

Geological facts

Flint and chert are essentially the same material, though 'flint' typically refers to the variety found specifically in chalk deposits. Because of its conchoidal fracture, it breaks into extremely sharp edges, making it one of the most important materials in human prehistory.

Field identification & locations

Easily identified by its smooth, water-worn exterior, waxy texture on freshly broken surfaces, high hardness (scratches glass), and characteristic conchoidal fracture. Commonly found along chalk cliffs, beaches, and riverbeds.

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