Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 4100 | Thousand metric tons | NA |
| 2003 | 4430 | Thousand metric tons | 8.05% |
| 2004 | 4580 | Thousand metric tons | 3.39% |
| 2005 | 5000 | Thousand metric tons | 9.17% |
| 2006 | 5040 | Thousand metric tons | 0.80% |
| 2007 | 5130 | Thousand metric tons | 1.79% |
| 2008 | 5136 | Thousand metric tons | 0.12% |
| 2009 | 5300 | Thousand metric tons | 3.19% |
| 2010 | 5300 | Thousand metric tons | 0.00% |
| 2011 | 5300 | Thousand metric tons | 0.00% |
| 2012 | 5300 | Thousand metric tons | 0.00% |
