The ornamental design for a diamond, as shown and described.
FIG. 1 is a top plan view of a diamond showing the first embodiment of my new design comprising a small table;
FIG. 2 is point-end elevational view;
FIG. 3 is a side elevational view;
FIG. 4 is a bottom plan view;
FIG. 5 is a top plan view of a diamond showing the second embodiment of my new design comprising a medium table;
FIG. 6 is point-end elevational view of FIG. 5;
FIG. 7 is a side elevational view of FIG. 5; and,
FIG. 8 is a bottom plan view of FIG. 5.
It being understood that the main feature of the present design for which patent protection is sought is the shape of the facets on the top of the diamond.