Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 288.213989257813 | Thousand metric tons | NA |
| 2004 | 316.024993896484 | Thousand metric tons | 9.65% |
| 2005 | 325 | Thousand metric tons | 2.84% |
| 2006 | 360 | Thousand metric tons | 10.77% |
| 2007 | 341 | Thousand metric tons | -5.28% |
| 2008 | 300 | Thousand metric tons | -12.02% |
| 2009 | 342 | Thousand metric tons | 14.00% |
| 2010 | 327 | Thousand metric tons | -4.39% |
| 2011 | 295 | Thousand metric tons | -9.79% |
| 2012 | 345 | Thousand metric tons | 16.95% |
