Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 12700 | Thousand metric tons | NA |
| 2004 | 12800 | Thousand metric tons | 0.79% |
| 2005 | 14400 | Thousand metric tons | 12.50% |
| 2006 | 13800 | Thousand metric tons | -4.17% |
| 2007 | 13800 | Thousand metric tons | 0.00% |
| 2008 | 13800 | Thousand metric tons | 0.00% |
| 2009 | 19759 | Thousand metric tons | 43.18% |
| 2010 | 17656 | Thousand metric tons | -10.64% |
| 2011 | 16369 | Thousand metric tons | -7.29% |
| 2012 | 13946 | Thousand metric tons | -14.80% |
| 2013 | 13870 | Thousand metric tons | -0.54% |
