Chert (Jasper/Agate variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Multi-colored (red, brown, grey, yellowish); Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or precipitation from silica-saturated waters in sedimentary environments. Can be found in various geological ages from Precambrian to Cenozoic.

Uses & Applications

Historically used for stone tools (knapping); currently used for lapidary work, jewelry (cabochons), and decorative landscaping stones.

Geological Facts

Because of its conchoidal fracture, it was the primary material used by prehistoric humans to create arrowheads, spear points, and scrapers.

Field Identification & Locations

Identify in the field by its hardness (scratches glass), waxy appearance, and smooth, shell-like (conchoidal) fractures. Common in river beds, gravel deposits, and limestone formations.

Identified on: 4/19/2026

Mode: Standard