Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 112.502998352051 | Thousand metric tons | NA |
| 2004 | 121.295997619629 | Thousand metric tons | 7.82% |
| 2005 | 131.231994628906 | Thousand metric tons | 8.19% |
| 2006 | 136.190002441406 | Thousand metric tons | 3.78% |
| 2007 | 121.75 | Thousand metric tons | -10.60% |
| 2008 | 123 | Thousand metric tons | 1.03% |
| 2009 | 96 | Thousand metric tons | -21.95% |
| 2010 | 118 | Thousand metric tons | 22.92% |
| 2011 | 130.875 | Thousand metric tons | 10.91% |
| 2012 | 126 | Thousand metric tons | -3.72% |
| 2013 | 110 | Thousand metric tons | -12.70% |
