Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 249 | Thousand metric tons | NA |
| 2003 | 302 | Thousand metric tons | 21.29% |
| 2004 | 283.351989746094 | Thousand metric tons | -6.17% |
| 2005 | 302.066009521484 | Thousand metric tons | 6.60% |
| 2006 | 364.432006835938 | Thousand metric tons | 20.65% |
| 2007 | 227.697006225586 | Thousand metric tons | -37.52% |
| 2008 | 225 | Thousand metric tons | -1.18% |
| 2009 | 156.899993896484 | Thousand metric tons | -30.27% |
| 2010 | 147.102996826172 | Thousand metric tons | -6.24% |
| 2011 | 79.5210037231445 | Thousand metric tons | -45.94% |
| 2012 | 64.7529983520508 | Thousand metric tons | -18.57% |
| 2013 | 65 | Thousand metric tons | 0.38% |
