Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 6876 | Thousand metric tons | NA |
| 2004 | 6947 | Thousand metric tons | 1.03% |
| 2005 | 6823 | Thousand metric tons | -1.78% |
| 2006 | 7119 | Thousand metric tons | 4.34% |
| 2007 | 7218 | Thousand metric tons | 1.39% |
| 2008 | 7313 | Thousand metric tons | 1.32% |
| 2009 | 5945.18603515625 | Thousand metric tons | -18.70% |
| 2010 | 6856.09619140625 | Thousand metric tons | 15.32% |
| 2011 | 7112.953125 | Thousand metric tons | 3.75% |
| 2012 | 6671.51904296875 | Thousand metric tons | -6.21% |
| 2013 | 6700 | Thousand metric tons | 0.43% |
