Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 28 | Thousand metric tons | NA |
| 2003 | 31 | Thousand metric tons | 10.71% |
| 2004 | 36.4659996032715 | Thousand metric tons | 17.63% |
| 2005 | 36.4560012817383 | Thousand metric tons | -0.03% |
| 2006 | 42.1910018920898 | Thousand metric tons | 15.73% |
| 2007 | 40 | Thousand metric tons | -5.19% |
| 2008 | 40 | Thousand metric tons | 0.00% |
| 2009 | 37.4000015258789 | Thousand metric tons | -6.50% |
| 2010 | 20.3299999237061 | Thousand metric tons | -45.64% |
| 2011 | 29.7099990844727 | Thousand metric tons | 46.14% |
| 2012 | 34.8899993896484 | Thousand metric tons | 17.44% |
| 2013 | 36.5 | Thousand metric tons | 4.61% |
