Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 1323 | Thousand metric tons | NA |
| 2003 | 1391 | Thousand metric tons | 5.14% |
| 2004 | 1265 | Thousand metric tons | -9.06% |
| 2005 | 1131 | Thousand metric tons | -10.59% |
| 2006 | 1311 | Thousand metric tons | 15.92% |
| 2007 | 1300 | Thousand metric tons | -0.84% |
| 2008 | 1300 | Thousand metric tons | 0.00% |
| 2009 | 1212 | Thousand metric tons | -6.77% |
| 2010 | 1290 | Thousand metric tons | 6.44% |
| 2011 | 1320 | Thousand metric tons | 2.33% |
| 2012 | 1400 | Thousand metric tons | 6.06% |
