Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 10600 | Thousand metric tons | NA |
| 2004 | 11000 | Thousand metric tons | 3.77 % |
| 2005 | 11000 | Thousand metric tons | 0.00 % |
| 2006 | 11000 | Thousand metric tons | 0.00 % |
| 2007 | 11000 | Thousand metric tons | 0.00 % |
| 2008 | 11300 | Thousand metric tons | 2.73 % |
| 2009 | 9310 | Thousand metric tons | -17.61 % |
