The ornamental design for a mosaictile, as shown and described.
FIG. 1 is a front view of a mosaic tile showing my new design;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof; and,
FIG. 4 is a bottom view thereof, the top view being a mirror image thereof.
The broken line showing of the webbing connecting the individual tiles, and the non-front surfaces of the tiles is for environmental purposes only and forms no part of the claimed design.