Source: United States Geological Survey (USGS) Minerals Resources Program
Note: Check source table for details and footnotes
| Year | Production | Unit of Measure | % Change |
| 2002 | 34640 | Thousand metric tons | NA |
| 2003 | 35500 | Thousand metric tons | 2.48% |
| 2004 | 33230.14453125 | Thousand metric tons | -6.39% |
| 2005 | 33917 | Thousand metric tons | 2.07% |
| 2006 | 35000 | Thousand metric tons | 3.19% |
| 2007 | 36000 | Thousand metric tons | 2.86% |
| 2008 | 38530 | Thousand metric tons | 7.03% |
| 2009 | 36910 | Thousand metric tons | -4.20% |
| 2010 | 39480 | Thousand metric tons | 6.96% |
| 2011 | 45240 | Thousand metric tons | 14.59% |
| 2012 | 51000 | Thousand metric tons | 12.73% |
