Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6234 | Thousand metric tons | NA |
| 2004 | 6011 | Thousand metric tons | -3.58% |
| 2005 | 6130 | Thousand metric tons | 1.98% |
| 2006 | 6159 | Thousand metric tons | 0.47% |
| 2007 | 5358 | Thousand metric tons | -13.01% |
| 2008 | 5138 | Thousand metric tons | -4.11% |
| 2009 | 4444 | Thousand metric tons | -13.51% |
| 2010 | 5429 | Thousand metric tons | 22.16% |
| 2011 | 4604 | Thousand metric tons | -15.20% |
| 2012 | 4900 | Thousand metric tons | 6.43% |
