Star ruby is a variety of ruby exhibhiting a star pattern so called asterism which is caused by oriented microscopic inclusions ,best exhibhited in a cabochon cut perpendicular to C-axis of a crystal.
The gem displays a sharp six rayed star which seems to glide magically across the surface of a gemstone .
The star formation can be best viewed under the single source of light such as sunlight or lamp.
The star ruby gemstone is rare because it is extensively difficult to find a high quality star ruby gemstone which reflects the star effect and good colour simultaneously .
The worth and rareness of this gemstone can be understood from the fact that even after mining of thousand pieces of corundum only a few of them exhibhit a star.
Often star ruby actually requires welcomed inclusions. Most star ruby is opaque with some finer material exhibhiting translucency.
A star ruby is not totally in red colour like normal ruby gemstone .The colour of the star ruby is purplish red ,brownish red,bordeaux red or pinkish red or even pinkish.
It is severely difficult to find a perfect coloured star ruby.Mostly it is found with some stripes or spots.
Cutting a star ruby necessitates bottoms inorder to properly orient and best display asterism star effect.It is very important that they are properly cut.They need to be cut into medium to high dome .Bottom of star rubies are kept unpolished so that light is trapped inside the gemstone.
The star should be sharp and not blurry . The best way to test sharpness of star is to look at star ruby in sunlight with dome facing sun. All six prongs should be straight and prominent.