Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 3645 | Thousand metric tons | NA |
| 2004 | 4036 | Thousand metric tons | 10.73% |
| 2005 | 4160 | Thousand metric tons | 3.07% |
| 2006 | 3432 | Thousand metric tons | -17.50% |
| 2007 | 3974 | Thousand metric tons | 15.79% |
| 2008 | 3995 | Thousand metric tons | 0.53% |
| 2009 | 4200 | Thousand metric tons | 5.13% |
| 2010 | 3572 | Thousand metric tons | -14.95% |
| 2011 | 3540 | Thousand metric tons | -0.90% |
| 2012 | 3570 | Thousand metric tons | 0.85% |
