Banded Chert

Physical Properties

Hardness: 6.5-7 Mohs; Color: Teal, blue-green, and purple/burgundy banding; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids. This specimen likely owes its vibrant secondary coloring to mineral inclusions like iron or manganese during diagenesis.

Uses & Applications

Used for lapidary work, cabochons, flintknapping due to its sharp edges, and as decorative landscape stone. Historically used for making tools and weapons.

Geological Facts

Chert is one of the most durable sedimentary rocks. Some banded varieties are colloquially called 'flint' or 'jasper' depending on their specific opacity and color profile.

Field Identification & Locations

Identify by its extreme hardness (scratches glass), waxy texture when smooth, and distinctive curved conchoidal fractures. Commonly found in stream beds or coastal gravels.

Identified on: 5/19/2026

Mode: Standard