Charonia lampas lampas shell is studied using scanning electron microscopy and X-ray diffraction combined analysis of the preferred orientations and cell parameters. The Charonia shell is composed of three crossed lamellar layers of biogenic aragonite. The outer layer exhibits a (0 0 1) fibre texture, the intermediate crossed lamellar layer is radial with a split of its c-axis and single twin pattern of its a-axis, and the inner layer is comarginal with split c-axis and double twinning. A lost of texture strength is quantified from the inner layer outward. Unit-cell refinements evidence the intercrystalline organic influence on the aragonite unit-cell parameters anisotropic distortion and volume changes in the three layers. The simulation of the macroscopic elastic tensors of the mineral part of the three layers, from texture data, reveals an optimisation of the elastic coefficient to compression and shear in all directions of the shell as an overall. (c) 2008 Elsevier Inc. All rights reserved.