Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2009 | 350.709014892578 | Thousand metric tons | NA |
| 2010 | 330.359008789063 | Thousand metric tons | -5.80% |
| 2011 | 388.153015136719 | Thousand metric tons | 17.49% |
| 2012 | 440 | Thousand metric tons | 13.36% |
| 2013 | 440 | Thousand metric tons | 0.00% |
