Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 4073 | Thousand metric tons | NA |
| 2004 | 5011 | Thousand metric tons | 23.03% |
| 2005 | 5200 | Thousand metric tons | 3.77% |
| 2006 | 5600 | Thousand metric tons | 7.69% |
| 2007 | 5600 | Thousand metric tons | 0.00% |
| 2008 | 5600 | Thousand metric tons | 0.00% |
| 2009 | 3755 | Thousand metric tons | -32.95% |
| 2010 | 4070 | Thousand metric tons | 8.39% |
| 2011 | 3969 | Thousand metric tons | -2.48% |
| 2012 | 3888 | Thousand metric tons | -2.04% |
| 2013 | 4000 | Thousand metric tons | 2.88% |
