I claim the ornamental design for a gemstone pavilion with sixty-four facets, as shown.
FIG. 1 is a side view of the gemstone pavilion with sixty-four facets showing my new design, it being under stood that this view is symmetric on the front, rear, left and right sides;
FIG. 2 is a bottom side view thereof; and,
FIG. 3 is a bottom perspective view thereof.
The crown of the gemstone is not shown and does not form part of the claimed design.
The characteristic feature of the design resides in the number of facets in the pavilion of the gemstone.