Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 32586 | Metric tons | NA |
| 2004 | 33000 | Metric tons | 1.27% |
| 2005 | 34000 | Metric tons | 3.03% |
| 2006 | 35000 | Metric tons | 2.94% |
| 2007 | 36000 | Metric tons | 2.86% |
| 2008 | 37000 | Metric tons | 2.78% |
