EVIDENCE OF ROTATION IN FLAME-STRUCTURE PEARLS FROM BIVALVES OF THE TRIDACNIDAE FAMILY

摘要

Thirty-seven pearls originating from bivalves of the Tridacnidae family were analyzed to determine their gemological properties and to characterize the optical features of their distinctive flame structure, terminating at the apex and base with patterns like those of blade impellers. All but two of the samples exhibited cylindrical symmetry around a fixed axis, suggesting a rotating movement during growth, as with numerous pearls from Pinctada margaritifera. One quite unusual feature, which is difficult to detect and to our knowledge has never before been described, consisted of spiral patterns at the apex and base of the pearl, and one of these patterns suggested the possibility of rotation. Other details that supported the conclusion of rotation during growth included comets associated with spot defects and pseudo-chatoyancy that appeared shifted to one side.