Engagement rings -- what you need to know

(InStyle.com) -- The holiday season is also the engagement season!

Yes, you read that right. It's been said that nearly 40 percent of all marriage proposals occur between Thanksgiving and Valentine's Day.

If you're one of the lucky ladies hoping for a ring this season (or one of the nervous gentlemen contemplating popping the question), use this guide to popular diamond shapes and cuts -- and the stars who sport them -- to get acquainted with the dazzling world of engagement rings.

Emerald

No shape more aptly fits the diamond nickname "ice" than the emerald, a rectangular cut with lean facets extending down the sides. 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.

Star Power: Eva Longoria, Ellen Pompeo, Melania Knauss

Asscher

The Asschers of Amsterdam, gem cutters for the British royal family, designed this striking, dramatic shape in 1902. A square with diagonally cropped corners and stepped sides, it features a high crown and sheds a gentle light.

Star Power: Tameka Foster, Ashlee Simpson, Christine Costner

Cushion

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.

Star Power: Jeri Ryan, Courtney Ford, Guiliana DePandi

Princess

Think of this flirty, flashy option as the "Yeah, baby!" stone, and not only because it was dreamt up in London during the swinging sixties. The arrangement of the gem's many (49 to 144) facets produces a hall-of-mirrors effect.

Star Power: Stephanie March, Kara Janx, Sarah Michelle Gellar

Oval

Ovals have been enjoying a high profile since Tom Cruise placed a gorgeous one on Katie Holmes's finger. The cool cousin of the round, the oval shares many of that stone's features, with plenty of sparkle and versatility when it comes to settings. The long shape is especially flattering.

Star Power: Bridgette Wilson, Toni Braxton, Rebecca Romijn

Pear

Made to sit with the point facing up, this lusciously feminine (and unusual) cut frequently goes solo because few wedding bands fit easily beneath the large underside of this stone.

Star Power: Katherine Heigl, Lela Rochon, Tiffany Fallon

Marquise

The name for this cut comes from 18th-century Versailles, where courtiers wore ship-shaped rings as a sign of their rank. Today the marquise can be worn lengthwise or sailing sideways across the finger.

Star Power: Catherine Zeta Jones, Victoria Beckham, Portia de Rossi

Round

Created by Marcel Tolkowsky in 1919, the round diamond is the most popular shape for engagement rings. It's often called the round brilliant because it has triangular facets, arranged to direct light from the bottom of the stone up through the top for maximum sparkle.

Star Power: Katherine McPhee, Roselyn Sanchez, Mary J. Blige

Radiant

This rectangular stone, introduced in the seventies, lives up to its name: By combining long, lean, step-cut and triangular facets, it refracts lots of light. So if you decide on this shape, keep the setting simple.

Star Power: Heidi Klum, Leslie Grossman, Anna Chlumsky

Rose-Cut

Most diamonds have a flat top with facets on the edges and bottom, but a rose-cut diamond is domed and covered with facets. Carat for carat, rose-cut diamonds, which cast a mellow, soft light, are typically less expensive than other shapes.

Star Power: Melissa Akey

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