Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 29570 | Thousand metric tons | NA |
| 2004 | 31000 | Thousand metric tons | 4.84% |
| 2005 | 30747 | Thousand metric tons | -0.82% |
| 2006 | 32926 | Thousand metric tons | 7.09% |
| 2007 | 35647 | Thousand metric tons | 8.26% |
| 2008 | 30982 | Thousand metric tons | -13.09% |
| 2009 | 25682 | Thousand metric tons | -17.11% |
| 2010 | 27361 | Thousand metric tons | 6.54% |
| 2011 | 28881.099609375 | Thousand metric tons | 5.56% |
| 2012 | 28513.5 | Thousand metric tons | -1.27% |
