The quality and value of any stone is evaluated on certain parameters.
Origin - Naturally occurring Star Ruby is principally mined in Sri Lanka, Burma, India and Africa. The deep red colour Star Ruby mined in Burma called Mogok Star Ruby is highly desired and valuable. Burmese mines produce the best quality stones but the mines have a low availability of Star Ruby. Thus, Star Ruby from Sri Lanka, India and Africa is more commercially sought after.
Colour - Star Rubies range in colour from pinkish-red to orangish-red to purplish-red to brownish-red. It is very difficult to find a perfectly coloured Star Ruby as the distribution of colour is often uneven in stripes or spots. Stones having a pure red colour with a hint of violet or blue called ‘pigeon-blood’ Star Ruby are regarded as the most valuable color variety.
Clarity - Star Rubies have needle-like rutile inclusions that cause the star phenomenon in them. An ideal Star Ruby would have enough inclusions for a well-defined star without compromising the stone’s transparency but even the best quality Star Rubies appear translucent to opaque.
Cut - Star Rubies are typically cut in smooth domed cabochon shape to bring out the star effect. Cuts which have a bright properly oriented star are highly rare and valuable.