Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2009 | 356.889007568359 | Thousand metric tons | NA |
| 2010 | 420.748992919922 | Thousand metric tons | 17.89% |
| 2011 | 410.467010498047 | Thousand metric tons | -2.44% |
| 2012 | 415 | Thousand metric tons | 1.10% |
| 2013 | 420 | Thousand metric tons | 1.20% |
