Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 9344 | Thousand metric tons | NA |
| 2004 | 9064 | Thousand metric tons | -3.00% |
| 2005 | 9100 | Thousand metric tons | 0.40% |
| 2006 | 9100 | Thousand metric tons | 0.00% |
| 2007 | 9100 | Thousand metric tons | 0.00% |
| 2008 | 9100 | Thousand metric tons | 0.00% |
| 2009 | 6452 | Thousand metric tons | -29.10% |
| 2010 | 8400 | Thousand metric tons | 30.19% |
| 2011 | 7521 | Thousand metric tons | -10.46% |
| 2012 | 7470 | Thousand metric tons | -0.68% |
| 2013 | 7470 | Thousand metric tons | 0.00% |
