Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 2852 | Thousand metric tons | NA |
| 2003 | 3500 | Thousand metric tons | 22.72% |
| 2004 | 4400 | Thousand metric tons | 25.71% |
| 2005 | 4600 | Thousand metric tons | 4.55% |
| 2006 | 4400 | Thousand metric tons | -4.35% |
| 2007 | 4900 | Thousand metric tons | 11.36% |
| 2008 | 4250 | Thousand metric tons | -13.27% |
| 2009 | 4900 | Thousand metric tons | 15.29% |
| 2010 | 5227 | Thousand metric tons | 6.67% |
| 2011 | 5500 | Thousand metric tons | 5.22% |
| 2012 | 5500 | Thousand metric tons | 0.00% |
