Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 5600 | Thousand metric tons | NA |
| 2004 | 6100 | Thousand metric tons | 8.93% |
| 2005 | 6300 | Thousand metric tons | 3.28% |
| 2006 | 5900 | Thousand metric tons | -6.35% |
| 2007 | 6000 | Thousand metric tons | 1.69% |
| 2008 | 6000 | Thousand metric tons | 0.00% |
| 2009 | 5400 | Thousand metric tons | -10.00% |
| 2010 | 6000 | Thousand metric tons | 11.11% |
| 2011 | 6200 | Thousand metric tons | 3.33% |
| 2012 | 6200 | Thousand metric tons | 0.00% |
| 2013 | 6200 | Thousand metric tons | 0.00% |
