Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2004 | 5700 | Thousand metric tons | NA |
| 2005 | 4902.498046875 | Thousand metric tons | -13.99% |
| 2006 | 4800 | Thousand metric tons | -2.09% |
| 2007 | 4800 | Thousand metric tons | 0.00% |
| 2008 | 4800 | Thousand metric tons | 0.00% |
| 2009 | 3351 | Thousand metric tons | -30.19% |
| 2010 | 3440 | Thousand metric tons | 2.66% |
| 2011 | 4231 | Thousand metric tons | 22.99% |
| 2012 | 3685 | Thousand metric tons | -12.90% |
| 2013 | 2300 | Thousand metric tons | -37.58% |
