Hi Zara - I'll start you off, but I'm sure others will weigh in. The 325 indicates 9k gold, which suggests it was made in England.
When the figure is etched below the surface, as opposed to being carved in low relief with the figure above, it is more properly called an intaglio.
Left facing figures are not so rare as all that & may simply indicate a left handed engraver. It is difficult to make your guy out, but if he is wearing a winged cap, could be Mercury or, as I believe, Perseus.
This is meant to look like the stone carnelian & possibly it is. But it may also be glass. It's being set in gold is no guarantee it is not. You would need a jeweler to make the determination unless you yourself can see the features that can give glass away, such as bubbles inside. Glass can be etched just like stone. But many pieces are molded. The telltale sign is the softness of the lines: too rounded to have been made by the sharp tools of the engraver.
The real value in the piece is that it belonged to your grandmother & was her gift to you. Enjoy it.
