sedimentary

Chert Nodules

Chert (SiO2)

Hardness: 7 on Mohs scale; Color: Grey, black, tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grey, black, tan
Luster: Waxy to dull

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, black, tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in sedimentary rocks, typically limestone or chalk, through the accumulation of silica-rich organic remains like sponges or radiolaria. Over time, silica replaces the host carbonate rock.

Uses & applications

Historically used for stone tools and weapons due to sharp fractures; currently used for road construction, landscaping, and flint-knapping enthusiasts.

Geological facts

These nodules are often called 'flint.' Because of their hardness and smooth fracture, they were the most important technological material for early humans making arrowheads and scrapers.

Field identification & locations

Identify by looking for rounded, lumpy shapes inside softer limestone layers. Test for hardness; it will easily scratch glass and produce a spark when struck with steel.