Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 3092 | Thousand metric tons | NA |
| 2004 | 3037 | Thousand metric tons | -1.78% |
| 2005 | 3056 | Thousand metric tons | 0.63% |
| 2006 | 3158 | Thousand metric tons | 3.34% |
| 2007 | 2914 | Thousand metric tons | -7.73% |
| 2008 | 2943 | Thousand metric tons | 1.00% |
| 2009 | 2042 | Thousand metric tons | -30.62% |
| 2010 | 2600 | Thousand metric tons | 27.33% |
| 2011 | 2600 | Thousand metric tons | 0.00% |
| 2012 | 2500 | Thousand metric tons | -3.85% |
