There are two ways to remove coal from the ground: surface mining and underground mining. Surface mining is used when a coal seam is relatively close to the surface, usually within 200 feet. The first step in surface mining is to remove and store the soil and rock covering the coal (called the overburden).
Pearl oysters are not closely related to true oysters, being members of a distinct family, the feathered oysters (Pteriidae). Both cultured pearls and natural pearls can be extracted from pearl oysters, though other molluscs, such as the freshwater mussels, also yield pearls of commercial value.
Abalone Pearls. The most colorful of all pearl producing mollusks, Abalone are found in rocky coastal waters around the world. Though fairly plentiful, these rock-hugging snails rarely produce pearls. When they do, the result can be incredibly beautiful. The colors range from vibrant greens, blues and pinks to silver and on some occasion white.