Chert (and Fossilized Brachiopod shell)

Physical Properties

Hardness 7 (Mohs scale), tan to brown color, vitreous to waxy luster, microcrystalline structure, conchoidal fracture, specific gravity 2.65.

Formation & Geological History

Formed through the precipitation of silica from seawater or volcanic ash, often replacing biological material like shells. Common in Paleozoic and Mesozoic limestone formations.

Uses & Applications

Used historically for tool-making (arrowheads) due to its sharp edges; used today as a decorative stone, in construction aggregate, and as a geological collecting specimen.

Geological Facts

The specimen appears to be a silicified brachiopod fossil or a chert nodule with a shape resembling organic matter. Chert is extremely durable and often preserves fine details of the organisms it replaces.

Field Identification & Locations

Identify in the field by its hardness (will scratch glass), waxy feel, and common association with limestone or chalk beds. Found globally in ancient seabed deposits.

Identified on: 4/28/2026

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