Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 3510 | Thousand metric tons | NA |
| 2003 | 3573 | Thousand metric tons | 1.79% |
| 2004 | 3580 | Thousand metric tons | 0.20% |
| 2005 | 3371 | Thousand metric tons | -5.84% |
| 2006 | 3724 | Thousand metric tons | 10.47% |
| 2007 | 3552 | Thousand metric tons | -4.62% |
| 2008 | 3544 | Thousand metric tons | -0.23% |
| 2009 | 2807 | Thousand metric tons | -20.80% |
| 2010 | 2136 | Thousand metric tons | -23.90% |
| 2011 | 1694 | Thousand metric tons | -20.69% |
| 2012 | 2000 | Thousand metric tons | 18.06% |
