Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 8.7819995880127 | Thousand metric tons | NA |
| 2004 | 9.10999965667725 | Thousand metric tons | 3.73% |
| 2005 | 11.4519996643066 | Thousand metric tons | 25.71% |
| 2006 | 15.1190004348755 | Thousand metric tons | 32.02% |
| 2007 | 13.664999961853 | Thousand metric tons | -9.62% |
| 2008 | 9.94799995422363 | Thousand metric tons | -27.20% |
| 2009 | 7.7519998550415 | Thousand metric tons | -22.07% |
| 2010 | 6.34499979019165 | Thousand metric tons | -18.15% |
| 2011 | 6.3289999961853 | Thousand metric tons | -0.25% |
| 2012 | 6 | Thousand metric tons | -5.20% |
| 2013 | 6 | Thousand metric tons | 0.00% |
