Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 3710 | Thousand metric tons | NA |
| 2004 | 3871 | Thousand metric tons | 4.34% |
| 2005 | 3730 | Thousand metric tons | -3.64% |
| 2006 | 3577 | Thousand metric tons | -4.10% |
| 2007 | 3815 | Thousand metric tons | 6.65% |
| 2008 | 3583 | Thousand metric tons | -6.08% |
| 2009 | 1966 | Thousand metric tons | -45.13% |
| 2010 | 3447 | Thousand metric tons | 75.33% |
| 2011 | 3240 | Thousand metric tons | -6.01% |
| 2012 | 2800 | Thousand metric tons | -13.58% |
