Keshi pearls are these unique-shaped irregular sized pearls that are technically an "accident" in pearl culturing.  These little guys aren't a product of a seeded oyster or mussel, they are made by the animal itself and spit out (rejected) because it wasn't a welcome seed to begin with.  As a result, these little pearls are made of nothing but nacre which is the luminous outer layer of the regular pearls themselves.  This makes these little "rejects" extremely lustrous and quite eye catching.  I love the irregularity of these pearls and gravitate to their shiny individual personalities.