I believe this Italian pietra dura (hard stone marquetry) panel was once inset into the lid of a brass or wood playing card box (one can find a range of examples out there with a quick search), but I was quite happy to find it on its own and would be inclined to hang it, perhaps in a gold frame, as a harbinger of good luck and fortune! Earlyish 20th century I believe, with a variety of semi-precious stones inlaid - lapis, malachite, etc. Lovely.

5 7/8" x 4" and in very good condition. The back is flat stone, not carved to fit a box, but shows what I presume is some residue from being adhered to the lid of a box. That surface is clean/not at all sticky.