Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 3771 | Thousand metric tons | NA |
| 2003 | 3613 | Thousand metric tons | -4.19% |
| 2004 | 3851 | Thousand metric tons | 6.59% |
| 2005 | 4022 | Thousand metric tons | 4.44% |
| 2006 | 4040 | Thousand metric tons | 0.45% |
| 2007 | 4000 | Thousand metric tons | -0.99% |
| 2008 | 4102 | Thousand metric tons | 2.55% |
| 2009 | 4163 | Thousand metric tons | 1.49% |
| 2010 | 4527 | Thousand metric tons | 8.74% |
| 2011 | 4577 | Thousand metric tons | 1.10% |
| 2012 | 4467 | Thousand metric tons | -2.40% |
