Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6600 | Thousand metric tons | NA |
| 2004 | 6900 | Thousand metric tons | 4.55% |
| 2005 | 6500 | Thousand metric tons | -5.80% |
| 2006 | 7057 | Thousand metric tons | 8.57% |
| 2007 | 7393 | Thousand metric tons | 4.76% |
| 2008 | 7400 | Thousand metric tons | 0.09% |
| 2009 | 6600 | Thousand metric tons | -10.81% |
| 2010 | 7761 | Thousand metric tons | 17.59% |
| 2011 | 8235 | Thousand metric tons | 6.11% |
| 2012 | 8300 | Thousand metric tons | 0.79% |
| 2013 | 8350 | Thousand metric tons | 0.60% |
