Spiral growth of calcitostracum

Abstract

SPIRAL growth hills built up of many tabular calcite microcrystals can be seen in definite regions of the growing surface of the left shell valve of the calcitostracum of Anomia lischkei under a reflexion microscope (Fig. 1). The spiral growth hill of calcitostracum contrasts interestingly with that of nacre1; the former is composed of many microcrystals of calcite distributed radially outwards2, whereas the latter is formed by many microcrystals of aragonite in nearly parallel orientation3,4 as Laue photographs and microscopes show. © 1968 Nature Publishing Group.