An “asterism” is an optical phenomenon occurred in typically corundum and other gems. When the stone is cut as a dome cabochon, a four to six rayed figure is displayed on the dome. Star stones get their asterism from the titanium dioxide inclusions of tiny fibers of rutile or silk. The stars are caused by the light reflecting from needle-like inclusions of rutile aligned perpendicular to the rays of the star.
"Sharing is caring", by Ivy Teong, Chief Designer, Juwelen Design. She is also the author for juwelendesign.blogspot.my or ivyteong.blogspot.com