This is a steampunk/vintage-style charm necklace, revealing that the reverse side of the circular key-pendant is encrusted with a ring of sparkling clear rhinestones- 1 missing. 

The necklace features:

• A large, gunmetal-finish key with a rhinestone-embellished circular frame

• A smaller accent skeleton key in an antique bronze tone

Determining an exact resale market value for an unbranded, mass-produced fashion necklace is difficult, but similar vintage-style skeleton key charm necklaces generally value between $10.00 and $25.00 on secondhand platforms like eBay and Mercari