Chert (Jasper/Flint variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, Opaque; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in sedimentary basins. This rounded specimen suggests significant water erosion in a river or beach environment.

Uses & Applications

Historically used for stone tools (knapping) due to its sharp conchoidal fracture. Modernly used in jewelry (as beach pebbles), landscaping, and as a raw material for silicon production.

Geological Facts

Chert was one of the most important minerals for early humans, used to create arrowheads, scrapers, and fire-starting tools. It is extremely resistant to chemical weathering.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, rounded 'river stone' texture. Look for conchoidal (shell-like) chips on edges. Commonly found in gravel pits, riverbeds, and coastal beaches.

Identified on: 4/27/2026

Mode: Standard