fossil

Agatized fossil clam/bivalve specimens

Fossil bivalve shells, partly replaced or infilled by chalcedony and quartz (SiO₂)

AI-generated identification · may be incorrect

Cream aragonite/calcite shell valves surround gray-white botryoidal chalcedony or microcrystalline quartz. Quartz hardness is about 6.5–7 Mohs, vitreous to waxy luster, while the shell material is softer and commonly shows layered growth lines.

Identified August 18, 2026More fossil →

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Physical properties

Formation & geological history

Marine bivalves were buried in sediment; groundwater later mineralized or replaced parts of the shells with silica. The exact geological age and locality cannot be determined from the image alone, but such specimens commonly come from Cenozoic sedimentary deposits.

Uses & applications

Primarily collector and educational specimens; polished examples are used as decorative objects. They have little industrial or jewelry use compared with ordinary agate.

Geological facts

The paired valves and concentric shell-growth structure support a bivalve identification. The gray interior is likely chalcedony or quartz rather than ordinary shell muscle imprint.

Field identification & locations

Identify by hinge symmetry, shell growth lines, and silica-filled cavities; test cautiously with hardness and acid, since acid can damage calcite shell material. Common sources include fossil-bearing volcanic ash and sedimentary basins.