A sparkling discovery on a prairie in central Montana. A mining official found kimberlite -- the molten rock in which diamonds are found, and preliminary tests have yielded a microscopic gem. It's believed to be the first diamond ever found in Montana that was created there, rather than dropped by a retreating glacier or other means. Large-scale exploration of the 80-acre site near Lewistown will begin next month. If more diamonds are found, the land could someday become the only working diamond mine in the U-S. Right now, the closest diamond mines are in Canada. Prospectors have plucked the gems from Montana stream beds and glacial valleys for years -- most notably the 14-carat Lewis and Clark diamond found in 1990.