Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2003 | 38.8559989929199 | Thousand metric tons | NA |
| 2004 | 32.1479988098145 | Thousand metric tons | -17.26 % |
| 2005 | 37.7900009155273 | Thousand metric tons | 17.55 % |
| 2006 | 36.2080001831055 | Thousand metric tons | -4.19 % |
| 2007 | 36.2000007629395 | Thousand metric tons | -0.02 % |
| 2008 | 36.2000007629395 | Thousand metric tons | 0.00 % |
| 2009 | 36 | Thousand metric tons | -0.55 % |
