sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, and white mottled patterns; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, and white mottled patterns
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater or as a replacement for biological remains (like radiolarians or diatoms) within marine sedimentary layers. Often occurs as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and fire-starting (flint); currently used in road construction, as an abrasive, and for lapidary work like tumbled stones.

Geological facts

Because it fractures conchoidally (like glass), it was the primary material used by prehistoric humans for arrowheads and knives. It is highly resistant to chemical weathering.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy feel, and characteristic smooth, curved fracture surfaces. Found worldwide, particularly in areas with limestone deposits.