sedimentary

Chert / Flint Nodule

Cryptocrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Varies from white, grey, brown to yellowish-tan (often with a weathered cortex). Luster: Waxy to vitreous on fresh fractures. Crystal structure: Microcrystalline or cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on the Mohs scale
Luster: Waxy to vitreous on fresh fractures

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms in marine environments through the replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the direct precipitation of silica from seawater, often over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and blades due to its conchoidal fracture. Also used historically in flintlock firearms and occasionally for decorative landscaping or building.

Geological facts

Chert and flint are chemically identical; the term 'flint' is often reserved for dark or black varieties found in chalk, while 'chert' refers to lighter varieties found in limestone.

Field identification & locations

Easily identified by its high hardness (scratches glass), conchoidal fracture, waxy luster, and the presence of a chalky or weathered outer cortex. Found worldwide in sedimentary rock formations.

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