Banded Chert (Jasper)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Dark brown with cream/tan banding; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. The banding often results from rhythmic deposition or secondary replacement of limestone/dolomite.

Uses & Applications

Used for making cabochons in jewelry, decorative landscaping, historical stone tools (due to conchoidal fracture), and as a collector's specimen.

Geological Facts

Chert is one of the most common materials used by prehistoric humans to create arrowheads and scrapers. Because it is so hard and chemically stable, it survives weathering much longer than surrounding rocks.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy luster when broken. Frequently found in riverbeds, glacial tills, and as nodules within limestone or chalk formations.

Identified on: 4/19/2026

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