Chert (Flint)

Physical Properties

Hardness: 7 Mohs scale. Color: Tan, beige, or yellowish-brown. Luster: Dull to waxy. Crystal Structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical replacement of limestone/dolomite by silica-rich fluids. Generally dates from various geological eras, frequently found in nodules within limestone beds.

Uses & Applications

Historically used for stone tools/weapons (knapping) and fire-starting. Currently used in road construction, as a filler in cement, and sometimes as a minor gemstone when colorful (Jasper).

Geological Facts

Chert breaks with a conchoidal fracture, creating sharp edges that made it the primary material for arrowheads and scrapers for prehistoric humans for thousands of years.

Field Identification & Locations

Identify by its hardness (scratches glass), waxy質感, and sharp, curved fracture lines. It is common in regions with large limestone or chalk deposits like the midwestern United States and southern England.

Identified on: 4/26/2026

Mode: Standard