sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, brown, or light grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Tan, brown, or light grey
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, or light grey; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwater within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today in road construction, as an abrasive, and occasionally for decorative landscaping.

Geological facts

Chert has been used by humans for millions of years to create tools. It is incredibly durable and resistant to chemical weathering, which is why it often remains as rounded nodules in soil or stream beds.

Field identification & locations

Identify in the field by its waxy luster and smooth, shell-like (conchoidal) fracture when broken. It is harder than steel and will scratch a knife blade. Found globally in sedimentary basins.