Twinning in Ramaura Synthetic Rubies

Twinned individuals of Ramaura synthetic rubies were examined. The crystals are penetration twins, the two components of which are symmetrically related by a 180 degree rotation about the c-axis or by a reflection across one of the first order hexagonal prisms {1010} or across the basal pinacoid (0001). The twins are in contact along four twin boundaries which are oriented parallel to the twin planes. This form of penetration twinning has never been encountered before in either natural or synthetic corundum.

Each twin crystal reveals one planar surface which represents the contact of the ruby with the floor of the crucible in which the growth procedure was performed. These planar surfaces of the twins are subdivided into different sectors by the four twin planes, which intersect at one central point. Triangular growth structures on basal planes are related by the symmetry elements of the twin, i.e. by a two-fold axis parallel to [0001] or by mirror planes parallel to {1010"}.

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