Zinc Based Alloy Galaxy Planet, Gold Plated Deep Blue Enamel 24mm x 16mm, Nip off the link with wire cutters and file if you want to include it in your mosaic....
With really flat tesserae like these, I usually glue something to the back of them. Usually a large seed bead, or even just a blob of thinset. This is to give it some height, so it doesn't get lost in your mosaic. Alternatively, these kind of tesserae can be glued on after a piece has been grouted and cleaned.
Don't be limited by your materials, play with your tess-array.
