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If the materials are not very old (Shells are often sent to accelerator mass spectrometry (AMS) labs for radiocarbon dating.A great proportion of shell materials sent to AMS labs for carbon 14 dating are mollusk shells.

Shellfish obtain carbon from the biosphere for shell building.

According to scientific studies, shellfish obtain organic carbon from marine or terrestrial plants and inorganic carbon from ocean water bicarbonate, atmospheric carbon dioxide, or freshwater bicarbonate.

However, we recommend 50-100 milligrams be sent to allow for an aggressive cleaning prior to the dating (and repeat analyses if necessary for confirming results based on quality control measures, at no additional cost to the client).

Most shells, corals, and other carbonate materials are cleaned by physical abrasion to remove the outer surfaces and any adhering carbonate material and are then acid etched to remove approximately 10-30% or greater of the total weight so that only the good primary carbonate is dated.

Shells are formed by the deposition of calcium carbonate crystals to an organic matrix, which is a protein called conchiolin.

This protein makes up only a few percent of the shell, hence the sample needed in the radiocarbon dating process is the inorganic portion.The use of the shell’s carbonate component presents problems because the substance is soluble and may isotopically or chemically exchange with its environment.When a shell exchanges carbon with soil acids around it, the shell’s carbon 14 ratio, and thus radiocarbon age, is altered.Although inorganic, the carbonate is still datable since its formation involves incorporation of carbon 14 from the biosphere.The carbonate present in shells is usually in the form of the mineral aragonite although some shells are mixtures of aragonite and calcite while others, like oyster shell, is mostly calcite.Studies show that the residence time of carbon 14 in the atmosphere ranges between 6 years and 10 years while the residence time of carbon 14 in oceans could take thousands of years.

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