Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 394000 | Metric tons | NA |
| 2004 | 402000 | Metric tons | 2.03% |
| 2005 | 416000 | Metric tons | 3.48% |
| 2006 | 420000 | Metric tons | 0.96% |
| 2007 | 420000 | Metric tons | 0.00% |
| 2008 | 420000 | Metric tons | 0.00% |
| 2009 | 420000 | Metric tons | 0.00% |
| 2010 | 420000 | Metric tons | 0.00% |
| 2011 | 420000 | Metric tons | 0.00% |
| 2012 | 420000 | Metric tons | 0.00% |
| 2013 | 420000 | Metric tons | 0.00% |
