Abstract
The crystalline structure of the nacre of Pinctada martensii was investigated with x-ray diffraction and the results were as follows:
1) The nacreous layer is found to be, not a single crystal, but aggregations of minute aragonite crystals all having their orthorhombic b and c axes parallel or nearly parallel to the fiber axes which are in agreement with the directions of growth parallel and normal to the inner shell surface, respectively.
2) The mode of the micro-crystal arrangements varies from portion to portion of nacres. 3) Orientation of crystallites seems to be more or less different between the discontinuous layers formed in the process of shell growth.
4) The crystalline structure of nacres is mosaic.
