Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 6980 | Thousand metric tons | NA |
| 2003 | 6550 | Thousand metric tons | -6.16 % |
| 2004 | 6715 | Thousand metric tons | 2.52 % |
| 2005 | 7594 | Thousand metric tons | 13.09 % |
| 2006 | 8192 | Thousand metric tons | 7.87 % |
| 2007 | 8200 | Thousand metric tons | 0.10 % |
| 2008 | 8200 | Thousand metric tons | 0.00 % |
