Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 443.14599609375 | Thousand metric tons | NA |
| 2004 | 451.205993652344 | Thousand metric tons | 1.82% |
| 2005 | 442.299987792969 | Thousand metric tons | -1.97% |
| 2006 | 442.092987060547 | Thousand metric tons | -0.05% |
| 2007 | 427.834014892578 | Thousand metric tons | -3.23% |
| 2008 | 389 | Thousand metric tons | -9.08% |
| 2009 | 345 | Thousand metric tons | -11.31% |
| 2010 | 356 | Thousand metric tons | 3.19% |
| 2011 | 334 | Thousand metric tons | -6.18% |
| 2012 | 349 | Thousand metric tons | 4.49% |
| 2013 | 346 | Thousand metric tons | -0.86% |
