Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 3500 | Metric tons | NA |
| 2003 | 3600 | Metric tons | 2.86 % |
| 2004 | 3700 | Metric tons | 2.78 % |
| 2005 | 3700 | Metric tons | 0.00 % |
| 2006 | 3900 | Metric tons | 5.41 % |
| 2007 | 3900 | Metric tons | 0.00 % |
| 2008 | 4000 | Metric tons | 2.56 % |
| 2009 | 4100 | Metric tons | 2.50 % |
