Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 340 | Thousand metric tons | NA |
| 2004 | 350.399993896484 | Thousand metric tons | 3.06% |
| 2005 | 351.399993896484 | Thousand metric tons | 0.29% |
| 2006 | 337.264007568359 | Thousand metric tons | -4.02% |
| 2007 | 353 | Thousand metric tons | 4.67% |
| 2008 | 315.5 | Thousand metric tons | -10.62% |
| 2009 | 271.902008056641 | Thousand metric tons | -13.82% |
| 2010 | 343.334991455078 | Thousand metric tons | 26.27% |
| 2011 | 354.028991699219 | Thousand metric tons | 3.11% |
| 2012 | 326.963012695313 | Thousand metric tons | -7.65% |
| 2013 | 324 | Thousand metric tons | -0.91% |
