Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 30902 | Thousand metric tons | NA |
| 2003 | 33322 | Thousand metric tons | 7.83% |
| 2004 | 28596.4296875 | Thousand metric tons | -14.18% |
| 2005 | 30387 | Thousand metric tons | 6.26% |
| 2006 | 33542.9765625 | Thousand metric tons | 10.39% |
| 2007 | 32744 | Thousand metric tons | -2.38% |
| 2008 | 32102 | Thousand metric tons | -1.96% |
| 2009 | 31704 | Thousand metric tons | -1.24% |
| 2010 | 37001 | Thousand metric tons | 16.71% |
| 2011 | 35705 | Thousand metric tons | -3.50% |
| 2012 | 39427 | Thousand metric tons | 10.42% |
