In her column in the Baltimore Sun, Rita St. Clair explained the appropriate mantel for a fireplace "situated between the living room and dining room and visible from both." St. Clair said this "type of fireplace" is "seldom accompanied by any mantel at all. In keeping with its minimalist styling, there are usually no decorative or framing elements around the firebox."
The type of fireplace you're describing is seldom accompanied by any mantel at all. In keeping with its minimalist styling, there are usually no decorative or framing elements around the firebox.
If you still prefer to add a mantel, your best option is probably to have it custom-designed, perhaps in Art Deco or Arts and Crafts styling. A local cabinetmaker should be able to create a wooden mantel of that kind with a handsome finish.
An alternate strategy involves calling attention to the wall around the fireplace. In this sophisticated contemporary setting, most of the wall has been covered with slab-sized ceramic tiles that form an integrated geometric pattern.
A contemporary fireplace doesn't need to be framed by a mantel. The main requirement is that the fireplace opening be surrounded with fireproof material to 6 inches minimum (building codes vary). This can be slate, marble or tile. Beyond that, you may extend the decorative treatment by covering a good part of the wall in tile or marble, or by using a contrasting paint.