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 | 6500 | Metric tons, gross weight | -10.96% |
| 2009 | 6700 | Metric tons, gross weight | 3.08% |
| 2010 | 5727 | Metric tons, gross weight | -14.52% |
| 2011 | 6204 | Metric tons, gross weight | 8.33% |
| 2012 | 6000 | Metric tons, gross weight | -3.29% |
