Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 15700 | Thousand metric tons | NA |
| 2003 | 16700 | Thousand metric tons | 6.37% |
| 2004 | 17200 | Thousand metric tons | 2.99% |
| 2005 | 18800 | Thousand metric tons | 9.30% |
| 2006 | 18500 | Thousand metric tons | -1.60% |
| 2007 | 17900 | Thousand metric tons | -3.24% |
| 2008 | 14400 | Thousand metric tons | -19.55% |
| 2009 | 10100 | Thousand metric tons | -29.86% |
| 2010 | 9560 | Thousand metric tons | -5.35% |
| 2011 | 9770 | Thousand metric tons | 2.20% |
| 2012 | 14800 | Thousand metric tons | 51.48% |
| 2013 | 15500 | Thousand metric tons | 4.73% |
