This elegant art deco shape received its confusing name during the 1920s, when it was typically used for emeralds. Characterized by a flat top and step-shaped side facets, an emerald cut cries out for a clean setting. Donald Trump gave Melania Knauss this style.

2.01-carat emerald-cut diamond with two tapered baguettes (.34 total carats) in platiunum, Kwiat, $29,375; 800-927-4367 or kwiat.com for stores.