Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 2300 | Thousand metric tons | NA |
| 2003 | 2400 | Thousand metric tons | 4.35% |
| 2004 | 2350 | Thousand metric tons | -2.08% |
| 2005 | 2400 | Thousand metric tons | 2.13% |
| 2006 | 2450 | Thousand metric tons | 2.08% |
| 2007 | 2500 | Thousand metric tons | 2.04% |
| 2008 | 2550 | Thousand metric tons | 2.00% |
| 2009 | 3877 | Thousand metric tons | 52.04% |
| 2010 | 3370 | Thousand metric tons | -13.08% |
| 2011 | 4918 | Thousand metric tons | 45.93% |
| 2012 | 3979 | Thousand metric tons | -19.09% |
| 2013 | 3538 | Thousand metric tons | -11.08% |
