sedimentary

Chert (Nodular Chert)

Microcrystalline or Cryptocrystalline Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, or light gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, beige, or light gray
Luster: Waxy to dull

Identified April 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or light gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the chemical precipitation of silica-rich fluids within sedimentary host rocks like limestone or chalk. Many cherts are of biogenic origin, derived from the remains of diatoms or sponges.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include road construction, landscaping, and occasionally as semi-precious gemstones when colorful (Jasper).

Geological facts

Chert was one of the most important prehistoric materials for survival. It is chemically identical to quartz but has a different internal structure. It can also preserve fossils in exquisite detail through a process called permineralization.

Field identification & locations

Identify in the field by its high hardness (it will scratch glass), its shell-like (conchoidal) fracture pattern, and a waxy or soapy texture on fresh surfaces. Commonly found in riverbeds and limestone outcrops.