sedimentary

Flint / Chert Pebble

Microcrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale; Color: Dark grey to brown with weathering patina; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline (chalcedony); Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on the Mohs scale
Color: Dark grey to brown with weathering patina
Luster: Waxy to vitreous

Identified August 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of limestone or chalk by silica-rich solutions or the accumulation of siliceous skeletal remains of marine organisms in ancient shallow seas, over millions of years.

Uses & applications

Historically used by early humans for making stone tools, arrowheads, and for fire-starting due to its conchoidal fracture and spark-producing properties.

Geological facts

Flint and chert are chemically identical, but 'flint' typically refers to the variety found in chalk or marly limestone formations, famous for prehistoric toolmaking.

Field identification & locations

Commonly found in stream beds, beaches, and glacial till where resilient silica rocks have survived transport; identifiable by its smooth water-worn exterior and sharp, conchoidal broken edges revealing darker interior material.

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