Is this a Cushion Cut?

[ladysuz]

Hello, I recently bought this ring, the hallmark dates it to 1810 but I dont know what the cut of the diamond is?
Is this a cushion cut? it is 5 x 4.75 mm and I am trying to guage the diamond size as well.Would it be more than half a carat? thanking anyone in advance for the help.

 

[Gypsy]

It's an OMB which is an early cushion cut. It's probably cut really deep (which is standard).

 

[ponder]

Gorgeous!