The 2001 value of nonfuel mineral production in Tennessee decreased by 5% from 2000 to $708 million. Crushed stone remained, by value, the leading commodity, accounting for about half the total nonfuel mineral value. Nationally, Tennessee ranked 21st in the total value of nonfuel minerals produced in 2001. Crushed stone has been the leading nonfuel mineral commodity produced in Tennessee for over 20 years, except for 1981. According to preliminary figures, in 2001, production was 60.5 million metric tons, valued at $372 million. Major rock types quarried to produce crushed stone were limestone, dolomite, and sandstone. Zinc, the state's leading nonfuel mineral commodity until 1981, remained the 2nd-leading mineral produced. Zinc was mined in Knox and Jefferson counties. Estimated ball clay production increased to 715,000 metric tons, with an estimated value of $30 million. The production of construction sand and gravel decreased from 8.76 million metric tons valued at $47 million in 2000 to 7.91 million metric tons valued at $43.1 million in 2001. In 2001, Tennessee led the nation in the value of natural gemstones produced. Tennessee was also 1st in ball clay, 2nd in zinc, 3rd in barite, 8th in fuller's earth, and 10th in industrial sand and gravel. Gemstone production consisted almost entirely of cultured freshwater pearls and mother-of-pearl derived from freshwater mussel shells.