Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 5764 | Thousand metric tons | NA |
| 2003 | 5913 | Thousand metric tons | 2.59% |
| 2004 | 5864.8837890625 | Thousand metric tons | -0.81% |
| 2005 | 5913.3828125 | Thousand metric tons | 0.83% |
| 2006 | 5795.92578125 | Thousand metric tons | -1.99% |
| 2007 | 5850 | Thousand metric tons | 0.93% |
| 2008 | 5800 | Thousand metric tons | -0.85% |
| 2009 | 5750 | Thousand metric tons | -0.86% |
| 2010 | 5700 | Thousand metric tons | -0.87% |
| 2011 | 5600 | Thousand metric tons | -1.75% |
| 2012 | 5500 | Thousand metric tons | -1.79% |
| 2013 | 5500 | Thousand metric tons | 0.00% |
