A diamond's resale value is determined by its cut, original value and popularity.
• Fancy shapes. Pear, heart and especially marquise shapes are not in high demand, said Pessis.
• Older cuts. Diamonds older than 1940 may have old mine or European cuts with less desirable facets and proportions. Some collectors, however, prefer them.
• Princess and square radiant cuts. They're still good, but they haven't held their value as much as round stones, said Jimmy Pessis, owner of Continental Diamond.
• A stone with a certificate from the European Gemological Laboratory (EGL) or International Gemological Institute (IGI). They are more lenient in grading, making them less valuable, said Marjory Torgerson, store manager at Be Iced in Edina.
• Round cuts. They never go out of style and they're easily the most popular-selling cut, said Patrick Nelson, diamond buyer at JB Hudson.
• Great cut. A quality cut maximizes brilliance.
• The bigger the better. Larger stones weighing 1 carat or more are easier to sell because of demand. Most couples buy ¾ carat or more.
• A certificate from the Gemological Institute of America (GIA) or the American Gem Society (AGS), both respected labs, establishes the diamond's value.