Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 365.837005615234 | Thousand metric tons | NA |
| 2004 | 419.954986572266 | Thousand metric tons | 14.79 % |
| 2005 | 437.595001220703 | Thousand metric tons | 4.20 % |
| 2006 | 500 | Thousand metric tons | 14.26 % |
| 2007 | 500 | Thousand metric tons | 0.00 % |
| 2008 | 500 | Thousand metric tons | 0.00 % |
| 2009 | 500 | Thousand metric tons | 0.00 % |
