Dual-Color Double Stars in Burmese Sapphire
A natural star sapphire with two stars of different coloration was described by Koivula and Tannous (2001). The two stars were observed singly but on opposite sides of the double cabochon—i.e., the color of the star visible depended upon whether the stone was viewed from the “top” dome or the “bottom” dome. One star was an “ordinary” white star of the type commonly seen in sapphires and rubies, caused by reflection from inclusions near the surface toward the viewer. The other was a yellow-brown star, caused by reflection from inclusions farther from the surface and thereby showing superimposition of the bodycolor of the host sapphire. Most natural asteriated rubies and sapphires are opaque or only slightly translucent and do not reveal the dual-color double stars that are the focus of this study. The gemstone showed two clearly separated six-rayed stars: one white star reflected from the dome of the cabochon and one yellow star confined to the curved base of the stone. In reflected light, the white and the bodycolored star were each visible regardless of the direction of view—i.e., when viewed toward the dome of the sample and when viewed toward the curved base . Moreover, in each viewing geometry, the bodycolored star was focused within the cabochon, and the white star was focused slightly outside the cabochon, between the sample and the observer.