Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 389.100006103516 | Thousand metric tons | NA |
| 2004 | 397.5 | Thousand metric tons | 2.16% |
| 2005 | 394.200012207031 | Thousand metric tons | -0.83% |
| 2006 | 349 | Thousand metric tons | -11.47% |
| 2007 | 408 | Thousand metric tons | 16.91% |
| 2008 | 408 | Thousand metric tons | 0.00% |
| 2009 | 360.307006835938 | Thousand metric tons | -11.69% |
| 2010 | 340 | Thousand metric tons | -5.64% |
| 2011 | 365 | Thousand metric tons | 7.35% |
| 2012 | 230 | Thousand metric tons | -36.99% |
| 2013 | 235 | Thousand metric tons | 2.17% |
