Gemmological properties

Striking picture of the structure of crystal faces which demonstrate a rhombohedral morphology

The gemmological properties are summarized in Tab. I. The colour of the gems varies from colourless to ordinary blue to fine royal blue. In most specimens the blue colour is not homogeneously distributed but rather forms blue phantoms or irregular blue patches and zones. This patchy coloration may be evened out by heat treatment resulting in a more homogeneous coloration and improvement in the quality of the hue.