Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 295 | Thousand metric tons | NA |
| 2004 | 296 | Thousand metric tons | 0.34% |
| 2005 | 298 | Thousand metric tons | 0.68% |
| 2006 | 300 | Thousand metric tons | 0.67% |
| 2007 | 300 | Thousand metric tons | 0.00% |
| 2008 | 300 | Thousand metric tons | 0.00% |
| 2009 | 128 | Thousand metric tons | -57.33% |
| 2010 | 128 | Thousand metric tons | 0.00% |
| 2011 | 128 | Thousand metric tons | 0.00% |
| 2012 | 130 | Thousand metric tons | 1.56% |
| 2013 | 125 | Thousand metric tons | -3.85% |
