Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 4679 | Thousand metric tons | NA |
| 2003 | 4824 | Thousand metric tons | 3.10% |
| 2004 | 4757 | Thousand metric tons | -1.39% |
| 2005 | 4700 | Thousand metric tons | -1.20% |
| 2006 | 4804 | Thousand metric tons | 2.21% |
| 2007 | 5104 | Thousand metric tons | 6.24% |
| 2008 | 5336 | Thousand metric tons | 4.55% |
| 2009 | 5605 | Thousand metric tons | 5.04% |
| 2010 | 6000 | Thousand metric tons | 7.05% |
| 2011 | 4000 | Thousand metric tons | -33.33% |
| 2012 | 4000 | Thousand metric tons | 0.00% |
