Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2009 | 511.06298828125 | Thousand metric tons | NA |
| 2010 | 601.046020507813 | Thousand metric tons | 17.61% |
| 2011 | 600 | Thousand metric tons | -0.17% |
| 2012 | 600 | Thousand metric tons | 0.00% |
| 2013 | 600 | Thousand metric tons | 0.00% |
