Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 15242 | Metric tons | NA |
| 2003 | 16755 | Metric tons | 9.93% |
| 2004 | 17569 | Metric tons | 4.86% |
| 2005 | 18433 | Metric tons | 4.92% |
| 2006 | 18444 | Metric tons | 0.06% |
| 2007 | 15972 | Metric tons | -13.40% |
| 2008 | 17320 | Metric tons | 8.44% |
| 2009 | 19575 | Metric tons | 13.02% |
| 2010 | 20190 | Metric tons | 3.14% |
| 2011 | 20373 | Metric tons | 0.91% |
| 2012 | 19702 | Metric tons | -3.29% |
| 2013 | 19300 | Metric tons | -2.04% |
