DOES ABALONE NACRE FORM BY HETEROEPITAXIAL NUCLEATION OR BY GROWTH THROUGH MINERAL BRIDGES

We present experimental support for a model of abalone nacre growth th at is based on mineral bridges between successive aragonite tablets ra ther than on heteroepitaxial nucleation. Interlamellar sheets of organ ic polymers delineate the aragonite tablets but allow the tablets to g row mineral bridges through pores in the sheets. Atomic force microsco pe images of interlamellar organic sheets from flat pearls made by Hal iotis rufescens (red abalone; marine gastropod mollusk) reveal a fibro us core and holes of 5-50 nm in diameter. Scanning ion conductance mic roscopy shows that these holes are actually pores through the interlam ellar sheets. With the help of statistical analysis we can associate t he pore-to-pore spacings in the interlamellar sheets with the observed offsets of successive nacre tablets. These results, supplemented by A FM, SEM, and TEM images, support and extend the model of biofabricatio n of gastropod nacre which is based on mineral bridges between the ara gonite tablets.