Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 3500 | Thousand metric tons | NA |
| 2004 | 3600 | Thousand metric tons | 2.86% |
| 2005 | 3300 | Thousand metric tons | -8.33% |
| 2006 | 4000 | Thousand metric tons | 21.21% |
| 2007 | 4000 | Thousand metric tons | 0.00% |
| 2008 | 4000 | Thousand metric tons | 0.00% |
| 2009 | 3500 | Thousand metric tons | -12.50% |
| 2010 | 3800 | Thousand metric tons | 8.57% |
| 2011 | 3900 | Thousand metric tons | 2.63% |
| 2012 | 3900 | Thousand metric tons | 0.00% |
| 2013 | 3900 | Thousand metric tons | 0.00% |
