Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 319.359985351563 | Thousand metric tons | NA |
| 2004 | 358.082000732422 | Thousand metric tons | 12.12% |
| 2005 | 379.630004882813 | Thousand metric tons | 6.02% |
| 2006 | 413.799987792969 | Thousand metric tons | 9.00% |
| 2007 | 419.059997558594 | Thousand metric tons | 1.27% |
| 2008 | 339.450012207031 | Thousand metric tons | -19.00% |
| 2009 | 359.385009765625 | Thousand metric tons | 5.87% |
| 2010 | 348.850006103516 | Thousand metric tons | -2.93% |
| 2011 | 278 | Thousand metric tons | -20.31% |
| 2012 | 272.5 | Thousand metric tons | -1.98% |
| 2013 | 216.399993896484 | Thousand metric tons | -20.59% |
