Chert (Jasper variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and reddish-orange due to iron oxides; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or via chemical precipitation from silica-rich fluids within sedimentary rock layers like limestone. This specimen appears to have undergone significant iron staining during or after formation.

Uses & Applications

Used historically for stone tools and arrowheads; currently used as ornamental stones, in jewelry (cabs), and as landscaping/fill material.

Geological Facts

Chert is so durable that it often survives as 'float' in stream beds long after the surrounding limestone has eroded away. Historically, high-quality cherts were some of the most traded materials among early human civilizations.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), its shell-like (conchoidal) fracture pattern, and its smooth, waxy texture compared to the surrounding rock. Common in limestone-rich regions.

Identified on: 4/14/2026

Mode: Standard