Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 545.6259765625 | Thousand metric tons | NA |
| 2004 | 553.684020996094 | Thousand metric tons | 1.48% |
| 2005 | 550 | Thousand metric tons | -0.67% |
| 2006 | 550 | Thousand metric tons | 0.00% |
| 2007 | 550 | Thousand metric tons | 0.00% |
