Just for clarification, “Kaka Neeli” is not a black shade of blue sapphire. It is actually a natural semi-precious blue gemstone known as Iolite. However, people in trade wrongly sell “Kaka Neeli” as kyanite which is another natural semi-precious blue gemstone. And mostly, “Kaka Neeli” is sold as real blue sapphire but actually it is a cost-effective alternative of blue sapphire.
I have written a post on how to identify blue sapphire at http://www.gemstonebuzz.com/forum/identification/455/how-to-identify-neelam-blue-sapphire#comment-113 (please go through it if you want to know).
Whatever gemstone you buy and from whom-ever you buy, always get it ccertified from a reputed gemological lab. It hardly costs around Rs. 1,000 to 1,500 to get it certified which is beneficial in the long run and for one’s statisfaction.
Just for infromation, we are based in Jaipur (gemstone hub of India) and deals in gemstone. In case you require ceritified natural gemstones at reasonable price then do contact us at http://www.gemstonebuzz.com/contact