Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 360 | Thousand metric tons | NA |
| 2003 | 360 | Thousand metric tons | 0.00% |
| 2004 | 360 | Thousand metric tons | 0.00% |
| 2005 | 360 | Thousand metric tons | 0.00% |
| 2006 | 360 | Thousand metric tons | 0.00% |
| 2007 | 360 | Thousand metric tons | 0.00% |
| 2008 | 381 | Thousand metric tons | 5.83% |
| 2009 | 298 | Thousand metric tons | -21.78% |
| 2010 | 237 | Thousand metric tons | -20.47% |
| 2011 | 365 | Thousand metric tons | 54.01% |
| 2012 | 317 | Thousand metric tons | -13.15% |
