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Abstract
Clays and their composing minerals have been mined since the Stone Age. Today they are among the most important minerals used for manufacturing and environmental industries. Clay minerals are hydrous-aluminosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths metals and other cations.
There are three types of bentonite: swelling bentonite (Na-bentonite), , non-swelling bentonite (Ca-bentonite) and sodium activated bentonites or sodium activated montmorillonites. Bentonite minerals occur as lenses or seams containing up to 50% moisture. They are rock like in nature and usually extracted by opencast mining (quarrying).