Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 7550 | Thousand metric tons | NA |
| 2003 | 8000 | Thousand metric tons | 5.96% |
| 2004 | 8000 | Thousand metric tons | 0.00% |
| 2005 | 9000 | Thousand metric tons | 12.50% |
| 2006 | 9000 | Thousand metric tons | 0.00% |
| 2007 | 9000 | Thousand metric tons | 0.00% |
| 2008 | 9400 | Thousand metric tons | 4.44% |
| 2009 | 9200 | Thousand metric tons | -2.13% |
| 2010 | 8300 | Thousand metric tons | -9.78% |
| 2011 | 8600 | Thousand metric tons | 3.61% |
| 2012 | 8600 | Thousand metric tons | 0.00% |
