Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 10200 | Thousand metric tons | NA |
| 2003 | 10400 | Thousand metric tons | 1.96% |
| 2004 | 11000 | Thousand metric tons | 5.77% |
| 2005 | 11000 | Thousand metric tons | 0.00% |
| 2006 | 11000 | Thousand metric tons | 0.00% |
| 2007 | 11000 | Thousand metric tons | 0.00% |
| 2008 | 14047 | Thousand metric tons | 27.70% |
| 2009 | 14519 | Thousand metric tons | 3.36% |
| 2010 | 14700 | Thousand metric tons | 1.25% |
| 2011 | 16300 | Thousand metric tons | 10.88% |
| 2012 | 16500 | Thousand metric tons | 1.23% |
