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.
The largest diamond found by a park visitor in the Crater of Diamonds State Park in Arkansas since 1972, when it was established as a state park. It was found by W. W. Johnson of Amarillo, Texas in 1975 and was a 16.37 carats (3.27 g) white diamond, but it has since been cut into a 7.54 carats (1,510 mg) marquise shape.