Susan Joyce,
Thank you for showing us these other views. I believe the inset material is mother of pearl - not enamel, the black looks like it is enamel and the metal looks like it is probably chrome - but hard to say for sure without handling it. I don't collect this type of jewelry, and don't know as much about it as others. The piece reminds me of Mid-Century Modern and may date to the period between 1945-1965. The construction is similar to some pieces pictured in Warman's Third Edition. It also has a Scandanavian "feel." Since there are no marks it is going to be difficult to pin it down unless you find something very similar. It's an interesting piece and should be fun to wear!