Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2004 | 4325 | Thousand metric tons | NA |
| 2005 | 3857 | Thousand metric tons | -10.82% |
| 2006 | 4265 | Thousand metric tons | 10.58% |
| 2007 | 3896 | Thousand metric tons | -8.65% |
| 2008 | 4000 | Thousand metric tons | 2.67% |
| 2009 | 3430 | Thousand metric tons | -14.25% |
| 2010 | 3400 | Thousand metric tons | -0.87% |
| 2011 | 3000 | Thousand metric tons | -11.76% |
| 2012 | 2500 | Thousand metric tons | -16.67% |
| 2013 | 3500 | Thousand metric tons | 40.00% |
