Mother of pearl, or MOP as it’s often abbreviated, is the iridescent inside layer of fresh- and salt-water shells like abalone and conch. Also known as nacre, mother of pearl is literally the stuff pearls are made of, hence its name. That “stuff” is about 95 percent aragonite, a hard, calcium-carbonate mineral secreted by the mollusk that lives inside the shell. Normally, aragonite is quite brittle, but when it forms into nacre on the inside of shells—and on the outside of pearls—the aragonite crystals arrange themselves in such a way that the material resists fracturing. This means mother of pearl can be carved into intricate cameos and cut into other shapes without breaking all to pieces.
Some of those shapes are geometric, inlaid into sterling silver earrings, bracelets, or rings and paired with contrasting stones such as onyx or turquoise. In other pieces of fine jewelry, such as pin and brooches, iridescent mother of pearl may be used replicate the shimmering surfaces of dragonfly wings. But it is in cameos that the material really shines, giving depth to a figure’s cheek bones and often putting a literal twinkle into a carving's eye.