Long after the wedding and through the marriage, one thing shines as brightly as it did at first _ the ring.

The bride's engagement ring stands out as the most significant part of wedding jewelry. Its stone represents the first serious jewelry investment for the couple, and its durability celebrates _ sentimentally and substantively _ their commitment to one another. Further, it will last beyond their lifetime, possibly to be enjoyed by their children.

The number one choice of stones remains the diamond, according to jewelry industry experts. Nearly 70 percent of all brides-to-be will receive rings with diamonds.

"The diamond will last forever, and the style of its setting should always reflect the taste of the wearer," says Melvyn Kirtley, vice president at Tiffany & Co.

However, colored gems, used alone or in combination with diamonds, are gaining in popularity, according to the November-December issue of Bridal Guide magazine.

"Before diamonds were readily available, colored gems were the betrothal stones of choice," says Diane Forden, the magazine's editor-in-chief. Top choices include sapphires, rubies, emeralds, topazes and amethysts, according to the magazine.

Whatever the selection, here are some basic facts, collected by Tiffany & Co., Bridal Guide magazine and the Diamond Information Center, representing De Beers:

Diamonds

Diamonds are tough, with a melting point 2« times higher than that of steel.

Discovered in India over 3,000 years ago, they have had a place in cultures around the world through history.

The Greeks considered them teardrops from the gods. Romans said diamonds came from falling stars that guided the arrow of Eros, the god of love. In the Middle Ages, the gems were thought to have magnetic powers that could hold couples together.

Diamond engagement rings are thought to have originated with European royalty in the 15th century.

Diamonds are judged by "the Four Cs" _ cut, color, clarity and carat. Cut refers to the jeweler's shaping of the raw stone, usually cutting 57 or 58 planes, or facets, that refract light and make the gem sparkle.

Color is the natural hue of the stone, which can range from pure white (the most prized) to diamonds with a hint of color. Clarity is a rating of the natural inclusions, or non-crystallized carbon traces, present in all diamonds; the fewer the inclusions, the rarer the stone. Carat is simply the weight of the stone; a carat is 0.2 grams. Jewelers express diamond weight in points _ 100 points to a carat.

The diamond's rating affects its cost. The Diamond Information Center suggests using two months of a groom's salary as guideline for the expenditure. Tiffany says simply that the choice should be the best the couple can afford.

Sapphires are the most prized of the blue stones, traditionally thought to symbolize innocence and truth. Alternate blue stones include aquamarine, iolite, blue topaz, spinel, tanzanite and tourmaline.

Rubies are the most expensive and rare of quality gemstones. By tradition, they are symbolic of love and passion. Alternative red stones include garnet, rubellite, and spinel.

Emeralds are soothingly green. According to tradition, master jewelers keep them nearby to rest their eyes periodically while working.

The stone traditionally symbolizes fertility, youth, and good luck. Other green stones include garnet, peridot, and sapphire.

The warm glow of yellow or orange is usually found in topaz, a symbol of friendship and fidelity. Alternate stones in these colors include beryl, citrine, and tourmaline.

A violet version of quartz, amethysts were worn by the ancient Romans to ward off the intoxicating powers of Bacchus, god of revelry. Other stones in the pink-to-violet range include morganite, pink sapphire and pink topaz.

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n The Tiffany & Co. "How To Buy a Diamond" guide is available in both print and video format through its stores. For information, call 1 (800) 526-0649.

n "How to Buy Diamonds You'll be Proud to Give" is a booklet available from the Diamond Information Center. Call 1 (800) FOREVER or visit the Web site at www.adiamondisforever.com.