Blank locket - possibly originally designed for glass insert or enameled picture? They hinge open with the front door of the locket - but it is open, see additional pics, like the front part is missing.
Anne-Marie is planning a class to use these with resin, so watch for that. Another fun component to get you creating.
They are pretty secure in their closing, you might need to pry them open the first couple of times.
32mm x 44mm By the each.