A perfect little Grand Tour micro mosaic in tiny sand-sized colored glass tesserae, depiction of the Coliseum among the ruins of Rome. The plaque has been set slightly off-kilter into an old Etruscan motif mount which acid-tests as 14k gold. It might be 15 or 16, as I don't have those acids to test. It does not test 18k. It has a remnant or hint of a gold strap added to the back, I'm assuming for a wide silk or velvet ribbon to thread through so it can be worn as a choker. Perfect for that, if you can get a goldsmith/jeweler to replace it, or add a brooch pin to back.
Very good to excellent condition for age and type. The micro mosaic plaque is excellent and undamaged. The gold mount may have been from a bracelet at one time, and has been altered (see back side) perhaps can be reworked as a pendant? I think one can quite readily adjust how it's resting in the mount. As it is, it won't fall out front or back but could be easily removed. One can see a little adhesive on back of unbroken plaque, which appears to be holding the plaque in place.