Pearls are organic gems, created when an oyster covers a foreign object with beautiful layers of nacre. Some time past, pearls were important financial assets, comparable in price to property, as many oysters would have to be looked for only 1 pearl. These were rare simply because were made only out of the blue.
Clip on earrings came about from the desire to protect ones ears from over bearing earrings that came about in the twentieth century. It became fashion to have ones ears pierced and then hang a huge number of items from a single piercing, this made people ears go red and throb badly.