Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 26000 | Metric tons | NA |
| 2003 | 26000 | Metric tons | 0.00% |
| 2004 | 28000 | Metric tons | 7.69% |
| 2005 | 27853 | Metric tons | -0.52% |
| 2006 | 24581 | Metric tons | -11.75% |
| 2007 | 29618 | Metric tons | 20.49% |
| 2008 | 32051 | Metric tons | 8.21% |
| 2009 | 19405 | Metric tons | -39.46% |
| 2010 | 23309 | Metric tons | 20.12% |
| 2011 | 26284 | Metric tons | 12.76% |
| 2012 | 27292 | Metric tons | 3.84% |
| 2013 | 28000 | Metric tons | 2.59% |
