Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 5600 | Thousand metric tons | NA |
| 2004 | 6100 | Thousand metric tons | 8.93 % |
| 2005 | 6300 | Thousand metric tons | 3.28 % |
| 2006 | 5900 | Thousand metric tons | -6.35 % |
| 2007 | 6000 | Thousand metric tons | 1.69 % |
| 2008 | 6000 | Thousand metric tons | 0.00 % |
| 2009 | 6000 | Thousand metric tons | 0.00 % |