Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 196.843994140625 | Thousand metric tons | NA |
| 2004 | 222.34700012207 | Thousand metric tons | 12.96% |
| 2005 | 239 | Thousand metric tons | 7.49% |
| 2006 | 255.800003051758 | Thousand metric tons | 7.03% |
| 2007 | 282.505004882813 | Thousand metric tons | 10.44% |
| 2008 | 264.752014160156 | Thousand metric tons | -6.28% |
| 2009 | 201 | Thousand metric tons | -24.08% |
| 2010 | 241 | Thousand metric tons | 19.90% |
| 2011 | 261 | Thousand metric tons | 8.30% |
| 2012 | 249 | Thousand metric tons | -4.60% |
| 2013 | 250 | Thousand metric tons | 0.40% |
