The most popular shape with brides, the round—often called the round brilliant—has triangular facets, arranged to direct light from the bottom of the stone up through the top for maximum sparkle. Matt Damon proposed with a ring that featured three round diamonds.

1.5-carat brilliant-cut round diamong with .57 carats of side stones in platinum, Scott Kay, $19,700; 866-654-5418 or scottkay.com for stores.