Topaz Ring; maybe Aquamarine

by Katie
(Monterey, CA)

I recently inherited a ring from my grandmother. It looks as if it is a blue topaz it could perhaps be an aquamarine. The gem is surrounded by many small diamonds.

The inside of the ring is stamped with RP
I'm curious if this ring is more valuable than I think it is, or if it is simply a piece of costume jewelry.
Thank You!