Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 19437 | Thousand metric tons | NA |
| 2003 | 19655 | Thousand metric tons | 1.12% |
| 2004 | 20962 | Thousand metric tons | 6.65% |
| 2005 | 21277 | Thousand metric tons | 1.50% |
| 2006 | 22540 | Thousand metric tons | 5.94% |
| 2007 | 22300 | Thousand metric tons | -1.06% |
| 2008 | 20895 | Thousand metric tons | -6.30% |
| 2009 | 17974 | Thousand metric tons | -13.98% |
| 2010 | 17733 | Thousand metric tons | -1.34% |
| 2011 | 19270 | Thousand metric tons | 8.67% |
| 2012 | 19500 | Thousand metric tons | 1.19% |
