Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 446 | Thousand metric tons | NA |
| 2004 | 476 | Thousand metric tons | 6.73% |
| 2005 | 424 | Thousand metric tons | -10.92% |
| 2006 | 401 | Thousand metric tons | -5.42% |
| 2007 | 395 | Thousand metric tons | -1.50% |
| 2008 | 369 | Thousand metric tons | -6.58% |
| 2009 | 366 | Thousand metric tons | -0.81% |
| 2010 | 348 | Thousand metric tons | -4.92% |
| 2011 | 283 | Thousand metric tons | -18.68% |
| 2012 | 340 | Thousand metric tons | 20.14% |
| 2013 | 350 | Thousand metric tons | 2.94% |
