Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 8000 | Thousand metric tons | NA |
| 2004 | 8200 | Thousand metric tons | 2.50% |
| 2005 | 8200 | Thousand metric tons | 0.00% |
| 2006 | 8200 | Thousand metric tons | 0.00% |
| 2007 | 8200 | Thousand metric tons | 0.00% |
| 2008 | 8200 | Thousand metric tons | 0.00% |
| 2009 | 7000 | Thousand metric tons | -14.63% |
| 2010 | 9500 | Thousand metric tons | 35.71% |
| 2011 | 10100 | Thousand metric tons | 6.32% |
| 2012 | 10800 | Thousand metric tons | 6.93% |
| 2013 | 10800 | Thousand metric tons | 0.00% |
