Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 16683.701171875 | Thousand metric tons | NA |
| 2003 | 17954.494140625 | Thousand metric tons | 7.62% |
| 2004 | 19196 | Thousand metric tons | 6.91% |
| 2005 | 21200 | Thousand metric tons | 10.44% |
| 2006 | 22100 | Thousand metric tons | 4.25% |
| 2007 | 20700 | Thousand metric tons | -6.33% |
| 2008 | 20650 | Thousand metric tons | -0.24% |
| 2009 | 24100 | Thousand metric tons | 16.71% |
| 2010 | 22200 | Thousand metric tons | -7.88% |
| 2011 | 27000 | Thousand metric tons | 21.62% |
| 2012 | 27000 | Thousand metric tons | 0.00% |
