Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 3300 | Thousand metric tons | NA |
| 2003 | 3500 | Thousand metric tons | 6.06% |
| 2004 | 3600 | Thousand metric tons | 2.86% |
| 2005 | 3621 | Thousand metric tons | 0.58% |
| 2006 | 5300 | Thousand metric tons | 46.37% |
| 2007 | 5206 | Thousand metric tons | -1.77% |
| 2008 | 5509 | Thousand metric tons | 5.82% |
| 2009 | 6500 | Thousand metric tons | 17.99% |
| 2010 | 7000 | Thousand metric tons | 7.69% |
| 2011 | 3500 | Thousand metric tons | -50.00% |
| 2012 | 2000 | Thousand metric tons | -42.86% |
