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 | 8500 | Thousand metric tons | -5.56 % |
