Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 290 | Thousand metric tons | NA |
| 2003 | 295 | Thousand metric tons | 1.72% |
| 2004 | 285 | Thousand metric tons | -3.39% |
| 2005 | 290 | Thousand metric tons | 1.75% |
| 2006 | 295 | Thousand metric tons | 1.72% |
| 2007 | 300 | Thousand metric tons | 1.69% |
| 2008 | 295 | Thousand metric tons | -1.67% |
| 2009 | 300 | Thousand metric tons | 1.69% |
| 2010 | 300 | Thousand metric tons | 0.00% |
| 2011 | 300 | Thousand metric tons | 0.00% |
| 2012 | 300 | Thousand metric tons | 0.00% |
