Star-Like Growth in Natural Yellow Sapphire

Ungkhana Atikarnsakul

Internal growth structures (commonly referred to as graining) observed in transparent gemstones often reflect a gem’s crystallography. Graining can assist in distinguishing natural from synthetic gem materials. For example, a synthetic flame-fusion corundum commonly shows curved growth lines, while natural and flux-grown corundum usually shows straight, angular, or hexagonal growth patterns.

Recently, the author examined an 8.01 ct faceted yellow stone that had gemological properties consistent with sapphire. The most distinctive feature found in this stone was internal graining displaying as six-rayed stars (see above). It is interesting to note that the angle of each ray was 60 degrees, consistent with corundum’s trigonal crystal structure. This is the first time the author has encountered a star-like graining pattern in natural sapphire.