Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6500 | Thousand metric tons | NA |
| 2004 | 5300 | Thousand metric tons | -18.46% |
| 2005 | 5100 | Thousand metric tons | -3.77% |
| 2006 | 5000 | Thousand metric tons | -1.96% |
| 2007 | 5000 | Thousand metric tons | 0.00% |
| 2008 | 5000 | Thousand metric tons | 0.00% |
| 2009 | 7442 | Thousand metric tons | 48.84% |
| 2010 | 8498 | Thousand metric tons | 14.19% |
| 2011 | 6286 | Thousand metric tons | -26.03% |
| 2012 | 8880 | Thousand metric tons | 41.27% |
| 2013 | 8752 | Thousand metric tons | -1.44% |
