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.
Many people believe that diamonds are formed from the metamorphism of coal. That idea continues to be the how diamonds form story in many science classrooms. Coal has rarely played a role in the formation of diamonds. In fact, most diamonds that have been dated are much older than Earth's first land plants - the source material of coal!