Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 6022 | Thousand metric tons | NA |
| 2003 | 6038 | Thousand metric tons | 0.27% |
| 2004 | 6661.5 | Thousand metric tons | 10.33% |
| 2005 | 6691 | Thousand metric tons | 0.44% |
| 2006 | 6932 | Thousand metric tons | 3.60% |
| 2007 | 7052 | Thousand metric tons | 1.73% |
| 2008 | 7559 | Thousand metric tons | 7.19% |
| 2009 | 7514 | Thousand metric tons | -0.60% |
| 2010 | 8070 | Thousand metric tons | 7.40% |
| 2011 | 7055 | Thousand metric tons | -12.58% |
| 2012 | 7241 | Thousand metric tons | 2.64% |
