This silver-tone pendant features a rectangular black onyx inlay and a reversible design. 

• Material: The metal is likely sterling silver (indicated by a 925 mark on similar pieces) with a black stone.

• Design: These pendants are often designed to be reversible, featuring a black inlay on one side and sometimes white enamel or a different stone on the other.

• Style: The minimalist rectangular shape is commonly seen in vintage jewelry from the 1990s or modern minimalist collections

• The estimated resale value of this reversible black onyx pendant ranges between $15 and $30 based on current marketplace trends.

  Mass Market / Fashion Pieces: the pendant is from a contemporary or fashion jewelry brand like Lia Sophia (which produced a very similar "Vice Versa" style slider pendant)