Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 4181 | Thousand metric tons | NA |
| 2004 | 4142 | Thousand metric tons | -0.93% |
| 2005 | 5169 | Thousand metric tons | 24.79% |
| 2006 | 5200 | Thousand metric tons | 0.60% |
| 2007 | 5300 | Thousand metric tons | 1.92% |
| 2008 | 5300 | Thousand metric tons | 0.00% |
| 2009 | 4000 | Thousand metric tons | -24.53% |
| 2010 | 3100 | Thousand metric tons | -22.50% |
| 2011 | 3500 | Thousand metric tons | 12.90% |
| 2012 | 3500 | Thousand metric tons | 0.00% |
| 2013 | 3000 | Thousand metric tons | -14.29% |
