Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 4.09800004959106 | Thousand metric tons | NA |
| 2004 | 4.84700012207031 | Thousand metric tons | 18.28% |
| 2005 | 6.50400018692017 | Thousand metric tons | 34.19% |
| 2006 | 7 | Thousand metric tons | 7.63% |
| 2007 | 7.5 | Thousand metric tons | 7.14% |
| 2008 | 7.59999990463257 | Thousand metric tons | 1.33% |
| 2009 | 7.40000009536743 | Thousand metric tons | -2.63% |
