Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 1000 | Thousand metric tons | NA |
| 2003 | 1080 | Thousand metric tons | 8.00% |
| 2004 | 1110 | Thousand metric tons | 2.78% |
| 2005 | 1100 | Thousand metric tons | -0.90% |
| 2006 | 1120 | Thousand metric tons | 1.82% |
| 2007 | 1100 | Thousand metric tons | -1.79% |
| 2008 | 1200 | Thousand metric tons | 9.09% |
| 2009 | 1200 | Thousand metric tons | 0.00% |
| 2010 | 1100 | Thousand metric tons | -8.33% |
| 2011 | 1200 | Thousand metric tons | 9.09% |
| 2012 | 1200 | Thousand metric tons | 0.00% |
