A: On the left: floating female figure (Selene) wearing peplos and a veil that forms a half-circle around her head and shoulders. Behind her shoulders the ends of a crescent. In her right hand a long bar (torch?), under her feet a round object (globe?). On the right: standing nude male figure with rays(?) on his head (Helios). Right arm raised in greeting, left hand holding a chlamys and a long bar (torch?).
B: Inscription in three lines: αρεδρει|αφοκρο|κυριλα → unidentified voces.
S. Michel suggests interpreting this gemstone as a love amulet (see link below).
Michel, BM on CBd-443
The British Museum Collection database on CBd-443