Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 13828 | Thousand metric tons | NA |
| 2003 | 13000 | Thousand metric tons | -5.99% |
| 2004 | 12594 | Thousand metric tons | -3.12% |
| 2005 | 11196 | Thousand metric tons | -11.10% |
| 2006 | 12000 | Thousand metric tons | 7.18% |
| 2007 | 12000 | Thousand metric tons | 0.00% |
| 2008 | 12000 | Thousand metric tons | 0.00% |
| 2009 | 13615.546875 | Thousand metric tons | 13.46% |
| 2010 | 11913.978515625 | Thousand metric tons | -12.50% |
| 2011 | 14657 | Thousand metric tons | 23.02% |
| 2012 | 15000 | Thousand metric tons | 2.34% |
| 2013 | 15000 | Thousand metric tons | 0.00% |
