Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 19200 | Thousand metric tons | NA |
| 2004 | 20000 | Thousand metric tons | 4.17% |
| 2005 | 20000 | Thousand metric tons | 0.00% |
| 2006 | 21000 | Thousand metric tons | 5.00% |
| 2007 | 20200 | Thousand metric tons | -3.81% |
| 2008 | 19900 | Thousand metric tons | -1.49% |
| 2009 | 15800 | Thousand metric tons | -20.60% |
| 2010 | 18300 | Thousand metric tons | 15.82% |
| 2011 | 19100 | Thousand metric tons | 4.37% |
| 2012 | 18800 | Thousand metric tons | -1.57% |
| 2013 | 19200 | Thousand metric tons | 2.13% |
