Plato lines?

Are the natural or plato lines?
This is under cross polarization and immersed in Isopropyl alcohol.

Hi Sterlinghelps!,

This is on which Gem?
I haven’t come across such pattern on diamonds as naturals or during polish.

Regards,
Nitin

The stone’s R.I. is 1.76 to 1.77. So my assumption is Corundum.