Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6116 | Thousand metric tons | NA |
| 2004 | 5735 | Thousand metric tons | -6.23% |
| 2005 | 6203 | Thousand metric tons | 8.16% |
| 2006 | 6276 | Thousand metric tons | 1.18% |
| 2007 | 6351 | Thousand metric tons | 1.20% |
| 2008 | 6409 | Thousand metric tons | 0.91% |
| 2009 | 4370 | Thousand metric tons | -31.81% |
| 2010 | 6259 | Thousand metric tons | 43.23% |
| 2011 | 5369 | Thousand metric tons | -14.22% |
| 2012 | 3711 | Thousand metric tons | -30.88% |
