The ornamental design for an oval faceted gemstone crown, as shown.
FIG. 1 is the top view of an oval faceted gemstone crown showing my new design;
FIG. 2 is a side view thereof; and,
FIG. 3 is an end view thereof. The pavillion is shown in broken lines in FIG. 2 and FIG. 3 for illustrative purposes only and forms no part of the claimed design.