Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 601.289978027344 | Thousand metric tons | NA |
| 2004 | 623.539978027344 | Thousand metric tons | 3.70% |
| 2005 | 615.070007324219 | Thousand metric tons | -1.36% |
| 2006 | 610 | Thousand metric tons | -0.82% |
| 2007 | 610 | Thousand metric tons | 0.00% |
| 2008 | 610 | Thousand metric tons | 0.00% |
| 2009 | 561.099975585938 | Thousand metric tons | -8.02% |
| 2010 | 335 | Thousand metric tons | -40.30% |
| 2011 | 380 | Thousand metric tons | 13.43% |
| 2012 | 200 | Thousand metric tons | -47.37% |
| 2013 | 160 | Thousand metric tons | -20.00% |
