Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 8378 | Thousand metric tons | NA |
| 2003 | 9339 | Thousand metric tons | 11.47% |
| 2004 | 9339 | Thousand metric tons | 0.00% |
| 2005 | 9400 | Thousand metric tons | 0.65% |
| 2006 | 9035.79296875 | Thousand metric tons | -3.87% |
| 2007 | 7562 | Thousand metric tons | -16.31% |
| 2008 | 5740 | Thousand metric tons | -24.09% |
| 2009 | 3540 | Thousand metric tons | -38.33% |
| 2010 | 2717 | Thousand metric tons | -23.25% |
| 2011 | 2555 | Thousand metric tons | -5.96% |
| 2012 | 2550 | Thousand metric tons | -0.20% |
| 2013 | 2654 | Thousand metric tons | 4.08% |
