Mosaic structure in the spines of Holopneustes porossisimus

Abstract

Sea urchin spines of Holopneustes porossisimus are porous single crystals, with the pores being filled with a material rich in carbon, silicon, fluorine and sodium. The magnesian calcite constituting the spine is highly strained. Even though the spines appear to be single crystalline on a macroscopic scale, the calcitic material exhibits an extended defect network. We find dislocations as well as rotational and other, not yet identified boundaries. We also observe within spine calcite a patterned distribution of sulphur. Both distributions, that of the defect network and that of sulphur resemble in their pattern to each other and have a similar mesh size of 50 nm. We conclude from these observations that they arise from the growth process of the spine and account for the mosaicity within the spine single crystals.