Beautiful blue color under incandescent light.   Similar blue in natural sunlight.  Violet under fluorescent.  Really a pretty looking stone and nice size as well at 5.10 cts.  Sri Lanka origin.  Color changer.   Rectangular scissor cut.  
No surface enhancements so no worries about cobalt diffusion.  This stone is NOT surface coated.  Neither are any of my other gems.  I buy direct from the miners and eliminate all the middle men so I can offer you the savings.   

Please be aware that I pride myself on bringing the best quality stones for the best possible prices.  I only select the best cut stones to offer my customers.   This stone has a slight veil inside I noticed under magnification.   Totally eye clean and nicely reflective.  Very rare type of spinel.  Changes color under fluorescent lighting.  
I try to price my stones below other sellers and try to make sure all customers are getting a true gemstone at a bargain price.  
There is an article on this site about blue spinel titled “The rarest of them all”.  It is located in the learn section under Additional Gemstone Information.

 https://www.gemrockauctions.com/learn/additional-gemstone-information/blue-spinel-the-rarest-of-them...

Spinel is rarely treated or heated as it naturally comes without many inclusions and heating does nothing to increase the beauty of the stones.  
Spinel is rapidly becoming more popular.  I’ve heard many gem affectionados state it was their favourite gemstone.  It was once thought to be sapphire or ruby depending upon the color.   The imperial crown housed in the tower of London has a large red spinel which was once thought to be a red ruby.  It is named the Black Prince’s Ruby and has a recorded history dating back to 1366 AD.
Cobalt is the main colorant in blue spinels and are especially rare.  For me I prefer them over sapphires.  The better price, less inclusions and lower cost make it the better value.  It is also a hardness of 8 which is only slightly under sapphire so is good for everyday wearing.