Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 31.8999996185303 | Thousand metric tons | NA |
| 2004 | 31.6000003814697 | Thousand metric tons | -0.94% |
| 2005 | 34.7000007629395 | Thousand metric tons | 9.81% |
| 2006 | 37 | Thousand metric tons | 6.63% |
| 2007 | 34.7999992370605 | Thousand metric tons | -5.95% |
| 2008 | 37.2999992370605 | Thousand metric tons | 7.18% |
| 2009 | 29.3999996185303 | Thousand metric tons | -21.18% |
| 2010 | 29.3999996185303 | Thousand metric tons | 0.00% |
| 2011 | 35.5999984741211 | Thousand metric tons | 21.09% |
| 2012 | 38 | Thousand metric tons | 6.74% |
| 2013 | 38 | Thousand metric tons | 0.00% |
