Thermoplastics, in basic terms, are melt-processable plastics (materials that are processed with heat). When enough heat is added to bring the temperature of the plastic above its melt point, the plastic liquefies (softens enough to be processed).
In the U.S., diamonds have been found in Arkansas, Colorado, Wyoming, and Montana. In 2004, the discovery of a microscopic diamond in the U.S. led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of Montana.
Outside the earth, diamonds are also common. A recent discovery shows that some stars collapse on themselves, creating giant diamond crystals. In the constellation Centaurus, there lies a white dwarf, that has crystallized into a diamond 2,500 miles in diameter and weighing 10 billion, trillion, trillion carats. While we are still learning about the interior of the earth, current information shows that diamonds are likely the most common gem in nature.