Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 240 | Thousand metric tons | NA |
| 2004 | 240 | Thousand metric tons | 0.00 % |
| 2005 | 260 | Thousand metric tons | 8.33 % |
| 2006 | 250 | Thousand metric tons | -3.85 % |
| 2007 | 260 | Thousand metric tons | 4.00 % |
| 2008 | 250 | Thousand metric tons | -3.85 % |
| 2009 | 260 | Thousand metric tons | 4.00 % |
