Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 350 | Thousand metric tons | NA |
| 2003 | 377 | Thousand metric tons | 7.71% |
| 2004 | 431.561004638672 | Thousand metric tons | 14.47% |
| 2005 | 467 | Thousand metric tons | 8.21% |
| 2006 | 443.799987792969 | Thousand metric tons | -4.97% |
| 2007 | 447.899993896484 | Thousand metric tons | 0.92% |
| 2008 | 572.885986328125 | Thousand metric tons | 27.90% |
| 2009 | 403.136993408203 | Thousand metric tons | -29.63% |
| 2010 | 540 | Thousand metric tons | 33.95% |
| 2011 | 559 | Thousand metric tons | 3.52% |
| 2012 | 328 | Thousand metric tons | -41.32% |
| 2013 | 100 | Thousand metric tons | -69.51% |
