Mother-of-pearl is the shiny, rainbow-colored material that lines the inside of certain seashells, especially oyster and abalone shells. If you've ever picked up a shell at the beach and noticed how the inside gleams with swirling colors that seem to shift between pink, blue, green, and silver, you were looking at mother-of-pearl.

The material forms naturally as the mollusk (the soft creature living inside the shell) builds up layers of a substance called nacre to protect itself. These layers are incredibly thin, thinner than a human hair, but they stack up in a way that bends light into different colors, creating that distinctive shimmer.

For thousands of years, craftspeople have prized mother-of-pearl for making beautiful objects. You might see it inlaid in furniture, jewelry boxes, or guitar fretboards. Pearl buttons on fancy shirts are often made from it. The material is both tough and beautiful, which makes it perfect for items that need to last while looking elegant.

Interestingly, pearls themselves are made of the exact same substance. When a grain of sand or other irritant gets inside an oyster's shell, the mollusk coats it with layer after layer of nacre, eventually forming a pearl. That's why pearls have the same lustrous glow as mother-of-pearl.