Star Phenomena in the Sapphire and Ruby Stones | Star Saphhires Identification
Corundum is one of precious stones. It gives us two beautiful varieties of precious stones those are sapphire and rubies.
Star phenomena in rubies and sapphires is common. That is due to their asterism or internal reflection. In cabochon form, star makes the low grade Corundum also valuable. Chemically, star sapphire is an aluminum oxide and forms as trigonal crystals. A window into a sapphire crystal showing its trigonal crystal symmetry; colorless silky center with nearly opaque blue outer growth.
Though being beautiful, the mysterious mechanism of internal reflection is quite simple. When a sapphire or rubies cool down from a semi liquid state, titanium dioxide present in it will crystalize after the sapphires cool down. During this, the structure becomes fixed.
After the formation or final processing of structure building in the sapphire, rutile needles grow following crystal structure while forming microscopic needles at 60 degree intervals. However, the star will only be visible If rutile's grow to sufficient density in 6 different directions. Than, the star will clearly be visible. The external light becomes the main reason of star by reflecting perpendicular to the rutile growth.
The cutting in star sapphires play a crucial part. Gem cutter must be precautions in order to get a well defined and proper oriented star. A sufficient and careful proper orientation for cutting star rubies and sapphires.
A distorted bi-pyramidal star sapphire crystal from Kyauk-pyat-that, Mogok, properly oriented for cutting into star stones.
Moreover, if you see any perfect star sapphire, be careful. There are lot of man mad, painted star sapphires in the market also. Always judge before buying. Generally star sapphires are not heated . Mostly comes natural.
The popular star sapphire is " Star of Asia" . It was 330 carats found in Srilanka. It was outstanding.