Clarity and colour make the difference, though Star Sapphires are usually opaque due to the amount of Rutile they contain. The Orientation of the Rutile needles within the stone creates the Star effect when they are cut.
Spinel is Softer and has a different Crystal habit, Bomb Sapphires are...
Like this?
This is from Australia, not perfect Imperial but close enough for me, Tests as Jadeite for RI, SG and hardness :)
The teardrop on the right is Burmese
Cheers
Wal