Is my Left Facing Cameo Rare or Special?

by Stefan D.
(East Longmeadow, MA, USA)

I inherited this Cameo from my mother, she bought it in Italy in the 60's, it's still in it's original case. I have been trying to decide between keeping it and selling it. I've been told the left facing ones are rare?

What I can say about it: 2-1/8" tall, 1-3/4" wide and about 3/4" tall, no scratches or cracks, has a small "800" marked on the rear bottom of the silver brim, has MxA (or M+A) carved into the back or the stone (?) material, not sure if real gold around the front. Comes with a necklace.

Is there anything else to know about it? Is it really rare or special?
What can I look at for a value if I were to try and sell it?

I'm grateful for any information, thank you kindly!