sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Variable (grey, brown, black); Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 7 on Mohs scale
Color: Variable (grey, brown, black)
Luster: Waxy to dull

Identified June 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Variable (grey, brown, black); Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed via the accumulation of silica-rich microfossils or chemical precipitation in marine environments; often occurs as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road surfacing, as grinding media, and for flint-striking fire starters.

Geological facts

Flint is a variety of chert that was essential to human survival for millennia due to its ability to produce sharp edges and sparks when struck against steel.

Field identification & locations

Identify by its smooth, waxy feel and distinctive shell-like (conchoidal) fracture edges. Look for nodules in sedimentary outcrops or as rounded pebbles in stream beds.