Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 3300 | Thousand metric tons | NA |
| 2004 | 3400 | Thousand metric tons | 3.03% |
| 2005 | 3600 | Thousand metric tons | 5.88% |
| 2006 | 3800 | Thousand metric tons | 5.56% |
| 2007 | 4000 | Thousand metric tons | 5.26% |
| 2008 | 4000 | Thousand metric tons | 0.00% |
| 2009 | 3800 | Thousand metric tons | -5.00% |
| 2010 | 4300 | Thousand metric tons | 13.16% |
| 2011 | 4300 | Thousand metric tons | 0.00% |
| 2012 | 4500 | Thousand metric tons | 4.65% |
| 2013 | 4500 | Thousand metric tons | 0.00% |
