Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 33372 | Thousand metric tons | NA |
| 2003 | 33593 | Thousand metric tons | 0.66% |
| 2004 | 34992.44140625 | Thousand metric tons | 4.17% |
| 2005 | 37451.6171875 | Thousand metric tons | 7.03% |
| 2006 | 40362 | Thousand metric tons | 7.77% |
| 2007 | 40670 | Thousand metric tons | 0.76% |
| 2008 | 37139 | Thousand metric tons | -8.68% |
| 2009 | 35160 | Thousand metric tons | -5.33% |
| 2010 | 34502 | Thousand metric tons | -1.87% |
| 2011 | 35400 | Thousand metric tons | 2.60% |
| 2012 | 36184 | Thousand metric tons | 2.21% |
