Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 9000 | Thousand metric tons | NA |
| 2003 | 9000 | Thousand metric tons | 0.00% |
| 2004 | 11000 | Thousand metric tons | 22.22% |
| 2005 | 12800 | Thousand metric tons | 16.36% |
| 2006 | 14701.572265625 | Thousand metric tons | 14.86% |
| 2007 | 15886 | Thousand metric tons | 8.06% |
| 2008 | 17397 | Thousand metric tons | 9.51% |
| 2009 | 18732 | Thousand metric tons | 7.67% |
| 2010 | 19100 | Thousand metric tons | 1.96% |
| 2011 | 19000 | Thousand metric tons | -0.52% |
| 2012 | 19000 | Thousand metric tons | 0.00% |
