Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 3892 | Thousand metric tons | NA |
| 2004 | 3765 | Thousand metric tons | -3.26% |
| 2005 | 3618 | Thousand metric tons | -3.90% |
| 2006 | 4145 | Thousand metric tons | 14.57% |
| 2007 | 4012 | Thousand metric tons | -3.21% |
| 2008 | 3529 | Thousand metric tons | -12.04% |
| 2009 | 3019 | Thousand metric tons | -14.45% |
| 2010 | 3649 | Thousand metric tons | 20.87% |
| 2011 | 3346 | Thousand metric tons | -8.30% |
| 2012 | 3400 | Thousand metric tons | 1.61% |
