Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 282.799987792969 | Thousand metric tons | NA |
| 2004 | 326.299987792969 | Thousand metric tons | 15.38% |
| 2005 | 325 | Thousand metric tons | -0.40% |
| 2006 | 312.299987792969 | Thousand metric tons | -3.91% |
| 2007 | 301.200012207031 | Thousand metric tons | -3.55% |
| 2008 | 301 | Thousand metric tons | -0.07% |
| 2009 | 300 | Thousand metric tons | -0.33% |
| 2010 | 300 | Thousand metric tons | 0.00% |
| 2011 | 300 | Thousand metric tons | 0.00% |
| 2012 | 110 | Thousand metric tons | -63.33% |
| 2013 | 50 | Thousand metric tons | -54.55% |
