So-called "conch pearls" (pronounced "konk") contain no nacre, so technically they are not actually pearls at all. Instead, the gems are calcareous concretions, similar to kidney stones in humans. They are produced by the Queen conch mollusk (Strombus gigas), which lives primarily in the Caribbean near southern Florida.

No one has yet devised a method for culturing conch pearls, so every one you see will be a natural pearl. Therefore, they are extremely rare and valuable. It is estimated that only one in 10,000 conchs produces a pearl, and that less than 10 percent of those are of gem quality.

Since the meat of the Queen conch is prized as food, it is generally harvested by fishermen, rather than being sought strictly for its pearls. The pearls tend to be "by-products," discovered by the fishermen as they harvest and clean their catch.

Conch pearls are usually small in size -- 3 millimeters or less -- and baroque or oval in shape. Colors are generally pink, yellow, brown, white, or golden. Pink (or a salmon-colored orange-pink) is generally the most sought-after color, while white and brown are relatively rare.

In addition to its often-striking colors, the conch pearl often has another important surface feature called a "flame structure," which is a unique pattern in the coloration. The flame structure generally appears in the pink or white-pink pearls, although the other colors sometimes also exhibit it.

An important fact to remember, if you are considering purchasing a conch pearl, is that its colors tend to fade significantly over time. Experts are not completely sure why, although sunlight is often cited as at least one factor in the fading. Thus, it's recommended that conch pearls be worn primarily in the evening and not exposed to excessive sunlight.

Since conch pearls are naturally both rare and unique, finding matching pearls for sets, earrings, strands, etc., is extremely difficult, thus significantly increasing both the cost and the value of such sets