If rose quartz is really a Diamon, why keep naming Quartz but not Rose Diamond? And then who is the true Rose Quartz (the gem not the name)?

This is what rose quarts looks like after being cut

This is what pink diamond looks like when cut

which looks more like

It’s possible that rose took on the name rose quartz as a way to say she’s no longer part of homeworld, no longer a diamond overlord. It’s also possible that diamond overlord is a title and not an actual gem.

It’s also likely that there are many types of gems. Because of what jasper said to pearl. that pearl is just “some lost, deformed pearl” it implies there are more pearls on homeworld.