Clay minerals can be an important agent in the fossilization of soft tissues, notably in the Ordovician Soom Shale of South Africa and the Cambrian Burgess Shale of Canada. The replication of morphology has been attributed to adsorption of pre-existing clay minerals, or direct precipitation of authigenic clays onto tissues. Attachment of quartz and kaolinite to the surface of lobster eggs demonstrates experimentally for the first time that soft tissues could fossilize in pre-existing minerals. However, the eggs became coated only in the presence of metabolizing bacteria. This experimental approach could be used to explore why Burgess Shale-type preservation declined after the mid-Cambrian.