Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 1748 | Thousand metric tons | NA |
| 2003 | 1644 | Thousand metric tons | -5.95% |
| 2004 | 1579 | Thousand metric tons | -3.95% |
| 2005 | 1644 | Thousand metric tons | 4.12% |
| 2006 | 1771 | Thousand metric tons | 7.73% |
| 2007 | 1898 | Thousand metric tons | 7.17% |
| 2008 | 1900 | Thousand metric tons | 0.11% |
| 2009 | 1898 | Thousand metric tons | -0.11% |
| 2010 | 1822 | Thousand metric tons | -4.00% |
| 2011 | 2021 | Thousand metric tons | 10.92% |
| 2012 | 1949 | Thousand metric tons | -3.56% |
| 2013 | 1950 | Thousand metric tons | 0.05% |
