Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 31500 | Metric tons | NA |
| 2003 | 28500 | Metric tons | -9.52% |
| 2004 | 29500 | Metric tons | 3.51% |
| 2005 | 26900 | Metric tons | -8.81% |
| 2006 | 27400 | Metric tons | 1.86% |
| 2007 | 33900 | Metric tons | 23.72% |
| 2008 | 30600 | Metric tons | -9.73% |
| 2009 | 29500 | Metric tons | -3.59% |
| 2010 | 35500 | Metric tons | 20.34% |
| 2011 | 37700 | Metric tons | 6.20% |
| 2012 | 34000 | Metric tons | -9.81% |
