National Ready Mixed Concrete Association:
Portland Cement Association:
Mineral Information Institute:
American Geosciences Institute:
Geological Society of America:
United States Geological Survey:
Minerals Information Institute – Reclaimed Aggregate Mines:
www.mii.org/reclindus.html#Sand%20and%20Gravel
National Energy Foundation Links on Aggregates:
http://www.nef1.org/outoftherock/index.html