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.
Because of the very special conditions required for the formation of diamond, and the rare volcanic events that bring them to the surface, gem diamonds that come within the reach of man are very rare. Diamonds have been found in a select number of kimberlites scattered around the planet.