PEARLS AREN'T EASY to buy. To the untrained eye, it's hard to tell why one necklace is $5,000 while one that looks similar is $1,500.

The key is to do some research and find a jeweler who understands and can explain pearls of all sorts--creamy Japanese Akoyas, black Tahitian gems, and other beauties.

These jewelers can.

Adeler Jewelers, 772-E Walker Rd., Great Falls; 703-759-4076; adelerjewelers.com. In business 30 years, Jorge Adeler knows pearls--and he'll give you a tutorial so you understand differences in luster, shape, and thickness. Besides pearls, this family-owned store sells other beautiful gemstones, and it does a lot of custom designs. Don't like a ring they made for you? They'll take it back.

Iridesse, Tysons Galleria; 703-356-6222; iridesse.com. Part of the Tiffany family, this new store sells nothing but pearls, backed by Tiffany's reputation and staffed by its knowledgeable sales force. Beautiful designs include golden South Sea beauties and pearls of silver blue.

Mikimoto, mikimotoamerica.com. The big name in pearls is Mikimoto, an international brand whose pearls are sold by, among others, Lynn Jewelers in DC, R. Bruce Carson Jewelers in Hagerstown, and Liljenquist & Beckstead, which has branches throughout Washington. Mikimoto's pearls are graded for quality, from A up to A+, AA, and AAA. That gives you some peace of mind, although you do pay for the name.

O'Rourke, 7950 Norfolk Ave., Bethesda; 301-656-4408. In business 37 years, master gemologist appraiser Edward O'Rourke is known for high standards. One pearl expert finds the prices high, but cultured pearls are a specialty here, and they're strung on the premises. The non-glitzy shop sells other gems, too, including antique pieces. Custom work is a third of sales, and O'Rourke does good repair--he can replicate an earring to replace one you lost.