Unusual strength properties of echinoderm calcite related to structure

Abstract

Echinoderm skeletons are composed of high-magnesium calcite having a fenestrate structure. Each skeletal ossicle appears to be a single crystal of calcium carbonate rather than a polycrystalline aggregate as, for example, are mollusc shells. Measurements of crushing strength for spines of three species of sea urchin demonstrate that the strength to weight ratio of these spines is equivalent to or greater than that of mollusc skeletons and most calcareous rocks. Echinoderms utilize calcium carbonate with unusually high efficiency, fulfilling the strength and volumetric requirements of a suitable skeleton with a minimum amount of material. Comparative dimensional analysis of structural and mechanical properties of these skeletal materials may provide further insight into the evolution of echinoderms. © 1969 Academic Press, Inc.