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 % |
