Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 298 | Thousand metric tons | NA |
| 2003 | 325 | Thousand metric tons | 9.06% |
| 2004 | 322.269989013672 | Thousand metric tons | -0.84% |
| 2005 | 340.696014404297 | Thousand metric tons | 5.72% |
| 2006 | 337.800994873047 | Thousand metric tons | -0.85% |
| 2007 | 294.183990478516 | Thousand metric tons | -12.91% |
| 2008 | 301 | Thousand metric tons | 2.32% |
| 2009 | 256 | Thousand metric tons | -14.95% |
| 2010 | 229 | Thousand metric tons | -10.55% |
| 2011 | 223 | Thousand metric tons | -2.62% |
| 2012 | 176 | Thousand metric tons | -21.08% |
