Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 239.738998413086 | Thousand metric tons | NA |
| 2004 | 245.005004882813 | Thousand metric tons | 2.20% |
| 2005 | 235.195999145508 | Thousand metric tons | -4.00% |
| 2006 | 236.740005493164 | Thousand metric tons | 0.66% |
| 2007 | 240 | Thousand metric tons | 1.38% |
