Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 11000 | Thousand metric tons | NA |
| 2003 | 13000 | Thousand metric tons | 18.18% |
| 2004 | 15000 | Thousand metric tons | 15.38% |
| 2005 | 17000 | Thousand metric tons | 13.33% |
| 2006 | 20652 | Thousand metric tons | 21.48% |
| 2007 | 30000 | Thousand metric tons | 45.26% |
| 2008 | 30800 | Thousand metric tons | 2.67% |
| 2009 | 32800 | Thousand metric tons | 6.49% |
| 2010 | 30000 | Thousand metric tons | -8.54% |
| 2011 | 32000 | Thousand metric tons | 6.67% |
| 2012 | 33000 | Thousand metric tons | 3.13% |
