Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2009 | 408.421997070313 | Thousand metric tons | NA |
| 2010 | 394.493011474609 | Thousand metric tons | -3.41% |
| 2011 | 381.177001953125 | Thousand metric tons | -3.38% |
| 2012 | 399.135009765625 | Thousand metric tons | 4.71% |
| 2013 | 480.399993896484 | Thousand metric tons | 20.36% |
