Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6645.255859375 | Thousand metric tons | NA |
| 2004 | 7800 | Thousand metric tons | 17.38% |
| 2005 | 8897 | Thousand metric tons | 14.06% |
| 2006 | 8400 | Thousand metric tons | -5.59% |
| 2007 | 7782 | Thousand metric tons | -7.36% |
| 2008 | 8400 | Thousand metric tons | 7.94% |
| 2009 | 8500 | Thousand metric tons | 1.19% |
| 2010 | 8500 | Thousand metric tons | 0.00% |
| 2011 | 4470 | Thousand metric tons | -47.41% |
| 2012 | 4594 | Thousand metric tons | 2.77% |
