sedimentary

Chert (or Chalcedony)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, white, and translucent gray; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, white, and translucent gray
Luster: Waxy to vitreous

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical precipitation of silica in groundwater within sedimentary host rocks. It can occur as nodules or bedded layers.

Uses & applications

Historically used for making stone tools due to its sharp edges; used today as a decorative landscaping stone, in construction aggregate, and occasionally for folk jewelry or as a collective specimen.

Geological facts

Chert has been used by humans for millions of years to create arrowheads and scrapers. When struck against steel, it can produce sparks, and it is a hard, durable material that resists weathering.

Field identification & locations

Identified in the field by its waxy texture, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) fracture pattern. Commonly found in limestone or chalk beds and along riverbed gravels.