sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Grayish-white to tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 (Mohs scale)
Color: Grayish-white to tan
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Grayish-white to tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of silica-rich microfossils (like radiolarians or diatoms) in marine sediments. Common in limestone and chalk deposits.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road construction, as an abrasive, and for geological study.

Geological facts

Chert and its variety, flint, were among the first materials used by early humans for tools because of their ability to break into sharp edges through conchoidal fracturing.

Field identification & locations

Identify in the field by its extreme hardness (scratches glass), waxy luster, and shell-like (conchoidal) fracture patterns. Frequently found as nodules within limestone or as river pebbles.