Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 3433 | Thousand metric tons | NA |
| 2003 | 3429 | Thousand metric tons | -0.12% |
| 2004 | 3857 | Thousand metric tons | 12.48% |
| 2005 | 4598 | Thousand metric tons | 19.21% |
| 2006 | 3785 | Thousand metric tons | -17.68% |
| 2007 | 4849 | Thousand metric tons | 28.11% |
| 2008 | 4697 | Thousand metric tons | -3.13% |
| 2009 | 3855 | Thousand metric tons | -17.93% |
| 2010 | 5814 | Thousand metric tons | 50.82% |
| 2011 | 6450 | Thousand metric tons | 10.94% |
| 2012 | 6300 | Thousand metric tons | -2.33% |
