Mosaic Medallions are made from small stones, tiles or glass pieces assembled together with grout gaps. It's typically attached to mesh on the back. Gaps between pieces have to be filled with grout. Medallions larger in size are more difficult to handle as the medallion is not solid; rather they are more flexible like a "pizza." Pieces may separate and get lost in transit or handling.
Tile Medallions are made from cutting standard off-the-shelf ceramic, porcelain or travertine tiles. These medallions are typically shipped as a set of labeled, precut tiles to be assembled on-site. The installer will have to put grout between the tiles and assemble the pieces. Medallions will have seem lines going across the surface. Solid stone pieces are very heavy and fragile, prone to breakage in transit and handling, and expensive to ship.