The term " black pearl" doesn't only apply to the ship that Johnny Depp was trying so hard to win back in Pirates of the Caribbean. Black also refers to a type of pearl found in the cold waters of the Pacific, most especially in and around Tahiti. Their " black" color, which I think is more like a really dark gray, is created by a type of oyster found in the Polynesian waters which secretes a dark liquid that colors the pearl growing inside of it. Like freshwater pearls, these pearls are farmed, but they are grown in the ocean and are harvested for the sole purpose of making jewelry. Collecting pearls from natural or wild oysters is illegal.

You can find out more information about black pearls here:

• My Hawaiian Jewelry - Ring pictured is from this site.
• Moorea Black Pearl - A nice FAQ on this web site.
• Black Pearl Jewelry - Fun myths and legends listed.