Comparisons of Microstructures and Hardness Distribution between Clinocardium Californiense and Veined Rapa Whelk Shells

Abstract

Abstract. Microstructures, phase compositions and microhardness distribution of two kinds of natural biological materials called Burnt-end Ark and Veined rapa whelk shells were studied and discussed for comparisons. It was found that the both shells present a hierarchical structure comprising three layers in thickness, i.e., inner, middle and outer layers. The inner and middle layers of the two kinds of shells exhibit cross-lamellar structures with somewhat of differences in the morphology and dimension. The outer layer presents a porous blocky structure for Burnt-end Ark shell and a layered structure for Veined rapa whelk shell. The X-ray diffraction (XRD) analyses show that all the layers of Burnt-end Ark shell as well as the inner and middle layers of Veined rapa whelk consist of crystalline aragonite CaCO3, while the out layer of Veined rapa whelk consists of crystalline calcite CaCO3. The microhardness measurements on the cross sections perpendicular to the growth lines of the shells demonstrate that the hardness of the both shells decreases gradually from the inner layer to the outer layer, strongly depending upon their microstructures.