Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 4000 | Thousand metric tons | NA |
| 2003 | 4000 | Thousand metric tons | 0.00% |
| 2004 | 5067.7998046875 | Thousand metric tons | 26.69% |
| 2005 | 5068 | Thousand metric tons | 0.00% |
| 2006 | 5700 | Thousand metric tons | 12.47% |
| 2007 | 6500 | Thousand metric tons | 14.04% |
| 2008 | 6600 | Thousand metric tons | 1.54% |
| 2009 | 6850 | Thousand metric tons | 3.79% |
| 2010 | 6872 | Thousand metric tons | 0.32% |
| 2011 | 6698 | Thousand metric tons | -2.53% |
| 2012 | 6800 | Thousand metric tons | 1.52% |
