Chert

Physical Properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and dark gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). Occurs as nodules or layered beds within limestone or shale.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative stone, in construction aggregate, and as a flint for fire-starting.

Geological Facts

This specimen displays a smooth, water-worn texture, suggesting it may have been tumbled in a river or stream. Varieties include flint, jasper, and agate. It was one of the most important materials for early human technology.

Field Identification & Locations

Identify in the field by its extreme hardness (will scratch glass), smooth waxy feel, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and limestone outcrops.

Identified on: 5/10/2026

Mode: Standard