Is This Blue Sapphire?

[Surya Giri]

I am not familiar with gemstone. But I was inherited this stone from my father. It was told that it was blue sapphire, and wheigted about 2.5 kgs (about 12,000 carats). I have tried to check to many gemology labs in my country, but it needs to be cut in order to be certificated because it is more than 1000 carats. Can some one help me to suggest what stone it is from the picture? In my country there are some fake blue obsidians sold in market, but this stone at least has been belong to my father since 40 years ago. Thank you in advance.

 

[Surya Giri]

I tried to make some picture in outdoor under the sun :

 

[Surya Giri]

I tried to make a photo with torch light from the other side of the stone :