[brikelly]

It makes sense now, but I guess I spent my life thinking this kind of process was actually cutting and not grinding. Well TIL.

[Retric]

The stage before what was shown may involve actual cutting/sawing and or cleavage. https://en.wikipedia.org/wiki/Cleavage_(crystal)

This allows you to preserve material for making multiple gems where grinding can only result in a single piece.