Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 5320 | Thousand metric tons | NA |
| 2003 | 5540 | Thousand metric tons | 4.14% |
| 2004 | 5630 | Thousand metric tons | 1.62% |
| 2005 | 5700 | Thousand metric tons | 1.24% |
| 2006 | 6160 | Thousand metric tons | 8.07% |
| 2007 | 6130 | Thousand metric tons | -0.49% |
| 2008 | 6415 | Thousand metric tons | 4.65% |
| 2009 | 6400 | Thousand metric tons | -0.23% |
| 2010 | 6400 | Thousand metric tons | 0.00% |
| 2011 | 6400 | Thousand metric tons | 0.00% |
| 2012 | 6400 | Thousand metric tons | 0.00% |
