Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 2500 | Thousand metric tons | NA |
| 2004 | 2600 | Thousand metric tons | 4.00% |
| 2005 | 2700 | Thousand metric tons | 3.85% |
| 2006 | 2800 | Thousand metric tons | 3.70% |
| 2007 | 2900 | Thousand metric tons | 3.57% |
