Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2004 | 2240 | Thousand metric tons | NA |
| 2005 | 2276 | Thousand metric tons | 1.61% |
| 2006 | 2565 | Thousand metric tons | 12.70% |
| 2007 | 2677 | Thousand metric tons | 4.37% |
| 2008 | 2843 | Thousand metric tons | 6.20% |
| 2009 | 2232 | Thousand metric tons | -21.49% |
| 2010 | 2130 | Thousand metric tons | -4.57% |
| 2011 | 2095 | Thousand metric tons | -1.64% |
| 2012 | 1831 | Thousand metric tons | -12.60% |
