best way to tweak this sapphire material?

I found this sapphire material in a blender material library online, but either it or the lighting doesn’t seem to be producing satisfying results. The sapphire ends up looking rather flat, as you can see. What would be the best way to make this more photorealistic? The sapphire’s mesh is hovering above a simple plane with a white diffuse shader. You can see the nodes to the sapphire itself.

Regardless of the solution, I’m hoping it’ll preserve or even increase the white star I crafted into the center-bottom of the gem.

It doesn’t have anything to reflect, and the lighting’s too soft to create any highlights. Use an HDRI to improve the reflections, and a sun or spotlight to add a sharper light source.