Centering an Oval cabochon star sapphire measuring approx. 16x14mm., fashioned in 18k yellow gold. Size 7 1/4.

The star in star sapphires is caused by the phenomenon known as asterism. Asterism occurs when silk (thin needle- like crystals of Rutile) orients in a regular triangular pattern. The rutile will cause light to reflect in a star with six rays. A natural star sapphire can not be heat treated because heating will melt the fine rutile which will destroy the star. Therefore we know all star sapphires are unheated.