A square with curved sides and rounded corners, this stone shines softly instead of sparkling. Cushion-cut center stones surrounded by tiny diamonds are especially in vogue. Superman star Brandon Routh chose a cushion-cut engagement ring for his fiance.

1.61-carat cushion-cut diamond with pave accents in platinum, Daniel K, $40,600; at Tiny Jewel Box, 202-393-2747.