Banded Chert (Jasper)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and dark bands; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.91

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids in sedimentary basins. This specimen shows water-worn rounding, likely from a stream or river bed.

Uses & Applications

Abrasives, jewelry (lapidary), primitive tool making (flint knapping), and aquarium/ornamental decor.

Geological Facts

Chert is so durable that it can survive millions of years of erosion. Famous for being used by early humans to create arrowheads and scrapers due to its sharp conchoidal edges when broken.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass) and its smooth, waxy feel. Often found in riverbeds or gravel pits. Look for the distinctive 'rings' or 'bands' that signify different layers of mineral deposition.

Identified on: 4/26/2026

Mode: Standard