Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 579 | Thousand metric tons | NA |
| 2003 | 420 | Thousand metric tons | -27.46% |
| 2004 | 461.212005615234 | Thousand metric tons | 9.81% |
| 2005 | 389.179992675781 | Thousand metric tons | -15.62% |
| 2006 | 400 | Thousand metric tons | 2.78% |
| 2007 | 400 | Thousand metric tons | 0.00% |
| 2008 | 300 | Thousand metric tons | -25.00% |
| 2009 | 335.188995361328 | Thousand metric tons | 11.73% |
| 2010 | 336.755004882813 | Thousand metric tons | 0.47% |
| 2011 | 337.272003173828 | Thousand metric tons | 0.15% |
| 2012 | 321.988006591797 | Thousand metric tons | -4.53% |
| 2013 | 338 | Thousand metric tons | 4.97% |
