Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 8554 | Thousand metric tons | NA |
| 2004 | 8828 | Thousand metric tons | 3.20% |
| 2005 | 8274 | Thousand metric tons | -6.28% |
| 2006 | 8305 | Thousand metric tons | 0.37% |
| 2007 | 8577 | Thousand metric tons | 3.28% |
| 2008 | 8770 | Thousand metric tons | 2.25% |
| 2009 | 5000 | Thousand metric tons | -42.99% |
| 2010 | 7666 | Thousand metric tons | 53.32% |
| 2011 | 7322.6240234375 | Thousand metric tons | -4.48% |
| 2012 | 7654.18017578125 | Thousand metric tons | 4.53% |
