In studies of organic matter in fossil biominerals, there has been a widespread failure to distinguish between the organic matrix and organic matter trapped within the crystal elements. The existence of chemically isolated (intracrystalline) proteins are indicated by the persistence of amino acids after prolonged treatment with a strong chemical oxidant (NaOCl). The geochemical significance of these residual amino acids is illustrated by the re-analysis of aberrantly young d-aile/l-ile ratios (0.142 ± 0.042, n = 4) of amino acids from a land snail (Cepaea sp.) collected from Tattershall Thorpe in Lincolnshire. Following NaOCl treatment the d-aile/l-ile ratio increased (0.178 ± 0.014, n = 5), while both the total amino acid concentration and the variance declined.