Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 27500 | Thousand metric tons | NA |
| 2004 | 29700 | Thousand metric tons | 8.00% |
| 2005 | 30600 | Thousand metric tons | 3.03% |
| 2006 | 28900 | Thousand metric tons | -5.56% |
| 2007 | 30100 | Thousand metric tons | 4.15% |
| 2008 | 30400 | Thousand metric tons | 1.00% |
| 2009 | 27500 | Thousand metric tons | -9.54% |
| 2010 | 32300 | Thousand metric tons | 17.45% |
| 2011 | 43800 | Thousand metric tons | 35.60% |
| 2012 | 50600 | Thousand metric tons | 15.53% |
| 2013 | 62100 | Thousand metric tons | 22.73% |
