Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 11218 | Thousand metric tons | NA |
| 2003 | 11500 | Thousand metric tons | 2.51% |
| 2004 | 12534 | Thousand metric tons | 8.99% |
| 2005 | 13000 | Thousand metric tons | 3.72% |
| 2006 | 11500 | Thousand metric tons | -11.54% |
| 2007 | 11500 | Thousand metric tons | 0.00% |
| 2008 | 11500 | Thousand metric tons | 0.00% |
| 2009 | 8181.4150390625 | Thousand metric tons | -28.86% |
| 2010 | 6990.2490234375 | Thousand metric tons | -14.56% |
| 2011 | 7825.7470703125 | Thousand metric tons | 11.95% |
| 2012 | 6360 | Thousand metric tons | -18.73% |
| 2013 | 6400 | Thousand metric tons | 0.63% |
