This is a lovely, vintage glass and butterfly wing cabochon set in sterling silver (marked 925).
NOTE: I think it could be turned into a lovely ring or pendant.
The size is roughly about 27 mm x 21 mm.
Some dings on the back of the pendant as shown in the photo. I have seen more "brillant" colors than this one, but this is still lovely - just has to be turned a certain way to really see the pretty colors.