Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 113.639999389648 | Thousand metric tons | NA |
| 2004 | 113.151000976563 | Thousand metric tons | -0.43% |
| 2005 | 114.223999023438 | Thousand metric tons | 0.95% |
| 2006 | 112.960998535156 | Thousand metric tons | -1.11% |
| 2007 | 113.436996459961 | Thousand metric tons | 0.42% |
| 2008 | 113 | Thousand metric tons | -0.39% |
| 2009 | 50 | Thousand metric tons | -55.75% |
| 2010 | 25 | Thousand metric tons | -50.00% |
| 2011 | 7 | Thousand metric tons | -72.00% |
