Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6500 | Thousand metric tons | NA |
| 2004 | 5062.8818359375 | Thousand metric tons | -22.11% |
| 2005 | 5100 | Thousand metric tons | 0.73% |
| 2006 | 5100 | Thousand metric tons | 0.00% |
| 2007 | 5000 | Thousand metric tons | -1.96% |
| 2008 | 5000 | Thousand metric tons | 0.00% |
| 2009 | 4965 | Thousand metric tons | -0.70% |
| 2010 | 5057 | Thousand metric tons | 1.85% |
| 2011 | 5073 | Thousand metric tons | 0.32% |
| 2012 | 3416 | Thousand metric tons | -32.66% |
| 2013 | 3400 | Thousand metric tons | -0.47% |
