Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 10600 | Thousand metric tons | NA |
| 2004 | 11000 | Thousand metric tons | 3.77% |
| 2005 | 11000 | Thousand metric tons | 0.00% |
| 2006 | 11000 | Thousand metric tons | 0.00% |
| 2007 | 11000 | Thousand metric tons | 0.00% |
| 2008 | 11300 | Thousand metric tons | 2.73% |
| 2009 | 9310 | Thousand metric tons | -17.61% |
| 2010 | 10600 | Thousand metric tons | 13.86% |
| 2011 | 10700 | Thousand metric tons | 0.94% |
| 2012 | 11100 | Thousand metric tons | 3.74% |
| 2013 | 11500 | Thousand metric tons | 3.60% |
