Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 31679 | Thousand metric tons | NA |
| 2003 | 32530 | Thousand metric tons | 2.69% |
| 2004 | 35626 | Thousand metric tons | 9.52% |
| 2005 | 37872 | Thousand metric tons | 6.30% |
| 2006 | 39408 | Thousand metric tons | 4.06% |
| 2007 | 35668 | Thousand metric tons | -9.49% |
| 2008 | 31651 | Thousand metric tons | -11.26% |
| 2009 | 33562 | Thousand metric tons | 6.04% |
| 2010 | 36496 | Thousand metric tons | 8.74% |
| 2011 | 36602 | Thousand metric tons | 0.29% |
| 2012 | 41047 | Thousand metric tons | 12.14% |
