Star Ruby, 5.20ct

About Star Rubies

Star Rubies are a very beautiful variety of the gemstone Ruby. The reason it is called a star ruby is that it displays a sharp six-rayed star due to an optical phenomenon called as ‘Asterism’. The star is clearly visible when seen under a single source of light like the sun or a lamp.

This star effect is due to the alignment of extremely fine needles or rutile or silk in the stones. When these stones are cut as cabochons, the light reflects off these tiny needles and gives the appearance of a moving six-rayed star on the surface of the stone. This star is not fixed, and it moves with the movement of the stone with respect to the light source.

It has a Mohs Hardness of 9 on a scale of 10, which makes it very suitable for daily wear. The Refractive index of rubies ranges from 1.762-1.778.

The irony is that since the star effect is caused due to the reflection of light as opposed to transmission - the sharper the star, the more included the stone tends to be. However, every once in a while there are stones which have a sharp asterism effect in combination with good transparency, and these stones are very rare. In many cases, the value of these stones is much more than the value of a faceted ruby of similar transparency.

Sometimes, the star ruby can display a twelve-rayed star or a double-star effect, which makes it even more invaluable.