Chert / Jasper

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Red, tan, and brown due to iron oxide inclusions; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65

Formation & Geological History

Formed through the accumulation of silica-rich fluids in sedimentary basins or by the replacement of limestone. Can range in age from Precambrian to Cenozoic depending on the deposit location.

Uses & Applications

Used historically for stone tools and arrowheads; currently used in jewelry (cabochons), as an abrasive, and in landscaping or collection.

Geological Facts

Because of its conchoidal fracture, it breaks with sharp edges, making it the primary material for prehistoric 'flint knapping' to create tools and weapons.

Field Identification & Locations

Identify in the field by its smooth, glass-like waxy texture on broken surfaces and its inability to be scratched by a steel knife. Frequently found in stream beds or limestone outcrops.

Identified on: 4/13/2026

Mode: Standard