Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 2650 | Thousand metric tons | NA |
| 2004 | 2850 | Thousand metric tons | 7.55% |
| 2005 | 3270 | Thousand metric tons | 14.74% |
| 2006 | 3850 | Thousand metric tons | 17.74% |
| 2007 | 4000 | Thousand metric tons | 3.90% |
| 2008 | 4000 | Thousand metric tons | 0.00% |
| 2009 | 1793 | Thousand metric tons | -55.18% |
| 2010 | 1995 | Thousand metric tons | 11.27% |
| 2011 | 2290 | Thousand metric tons | 14.79% |
| 2012 | 2149 | Thousand metric tons | -6.16% |
| 2013 | 2112 | Thousand metric tons | -1.72% |
