Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 520 | Thousand metric tons | NA |
| 2004 | 493.733001708984 | Thousand metric tons | -5.05% |
| 2005 | 443.878997802734 | Thousand metric tons | -10.10% |
| 2006 | 450 | Thousand metric tons | 1.38% |
| 2007 | 470 | Thousand metric tons | 4.44% |
| 2008 | 450 | Thousand metric tons | -4.26% |
| 2009 | 450 | Thousand metric tons | 0.00% |
| 2010 | 460 | Thousand metric tons | 2.22% |
| 2011 | 460 | Thousand metric tons | 0.00% |
| 2012 | 460 | Thousand metric tons | 0.00% |
| 2013 | 470 | Thousand metric tons | 2.17% |
