1) Monoclinic mineral 
Dickite (Al2Si2O5(OH)4) is a phyllosilicate clay mineral chemically composed of aluminium, silicon, hydrogen and oxygen contributing 20.90%, 21.76%, 1.56%, and 55.78% each respectively. It has the same composition as kaolinite, nacrite, and halloysite, but with a different crystal structure (polymorph). Dickite sometimes contains impurities such a...
clay mineral, a form of kaolinite (q.v.).[2 related articles]
a polymorph of kaolinite.