Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 6136 | Metric tons, gross weight | NA |
| 2003 | 6364 | Metric tons, gross weight | 3.72 % |
| 2004 | 6600 | Metric tons, gross weight | 3.71 % |
| 2005 | 6800 | Metric tons, gross weight | 3.03 % |
| 2006 | 7300 | Metric tons, gross weight | 7.35 % |
| 2007 | 7300 | Metric tons, gross weight | 0.00 % |
| 2008 | 7000 | Metric tons, gross weight | -4.11 % |
