Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 3980 | Thousand metric tons | NA |
| 2003 | 4000 | Thousand metric tons | 0.50 % |
| 2004 | 4604.201171875 | Thousand metric tons | 15.11 % |
| 2005 | 5107.2578125 | Thousand metric tons | 10.93 % |
| 2006 | 5782.4189453125 | Thousand metric tons | 13.22 % |
| 2007 | 6231.02294921875 | Thousand metric tons | 7.76 % |
| 2008 | 6921.73486328125 | Thousand metric tons | 11.09 % |
