Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 257 | Thousand metric tons | NA |
| 2003 | 260 | Thousand metric tons | 1.17% |
| 2004 | 260 | Thousand metric tons | 0.00% |
| 2005 | 260 | Thousand metric tons | 0.00% |
| 2006 | 260 | Thousand metric tons | 0.00% |
| 2007 | 228.600997924805 | Thousand metric tons | -12.08% |
| 2008 | 230 | Thousand metric tons | 0.61% |
| 2009 | 250 | Thousand metric tons | 8.70% |
| 2010 | 200 | Thousand metric tons | -20.00% |
| 2011 | 200 | Thousand metric tons | 0.00% |
| 2012 | 220 | Thousand metric tons | 10.00% |
