sedimentary

Chert (Nodule)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or light grey; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, or light grey
Luster: Dull to waxy

Identified February 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, brown, or light grey; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed by the precipitation of silica from groundwater within limestone or chalk beds. This specific specimen is a water-worn nodule, likely formed during the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include road surfacing, decorative garden stones, and as an industrial abrasive.

Geological facts

Chert is so hard it can create sparks when struck against steel. Nodules often take on bulbous, 'bone-like' or 'skull-like' shapes due to the way silica replaced organic or carbonate material.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, waxy feel. Found worldwide in sedimentary basins, riverbeds, and coastal areas.