Moose River Basin: geology and mineral potential - Geology Ontario

Lignite and Industrial Mineral Resources
are simple hydrous aluminosilicates; montmorillonites in addition carry iron
and magnesium. Illite or hydromica is characterised by the presence of potassi
um.
Most clays contain more than one clay mineral. Usefulness of clay as a fire
resistant or refractory raw material depends on the absence of fluxes like iron
and alkalies. Kaolinite is an extremely suitable refractory raw material. At
high temperatures it converts to an intergrowth of mullite and silica which im
parts strength to the refractory ceramic.
MINERALOGY
Kaolinitic clay or china clay is a white clay consisting predominantly of
hydrous aluminosilicates of the kaolinitic clay group. Kaolinite has the formu
la: Al4(Si4(OH) 8). The group includes polymorphs of this composition as well as
anauxite, which has a higher silica content, halloysite, with increased water
content and meta-halloysite, which develops from halloysite by partial reduc
tion of the water content.
The minerals of the kaolinitic clay group are characterised by a double
layer structure. A layer of silica tetrahedrons in hexagonal array at the base is
linked to a layer of aluminium hydroxide above by the shared oxygen atoms of
the upward pointing tops of the tetrahedrons. Additional water can be accom
modated between the hydroxyl groups of the aluminium hydroxide layer and
the oxygens of the next layer of silica tetrahedrons. Additional water is present
in halloysite, metahalloysite, and in a form of kaolinitic clay with tubular mor
phology, referred to as hydrated kaolinitic clay (Deer, Howie, and Zussman
1962, p. 198).
Kaolinite is white and has perfect basal cleavage. It has hardness of 2 to 2.5
and specific gravity of 2.61. The crystal platelets occur either individually, in
American clays usually concurring with grain sizes smaller than 2jx, or they oc
cur stacked in book form or vermicular shape exceeding 2jx in size (Lyons and
Bowman 1973, p.27). A third division commonly made is one of "Fines", smaller
than 0.25|x. Fines are known to occur in compact masses typical for ball clays.
A higher content of montmorillonite, 3 to 5 percent, often serves to make the
fines plastic and sufficiently strong for ceramic use.
The degree of stacking order of crystal platelets in books of kaolinitic clay
determines its specific use in other instances. Small, well-ordered blocky grains
or individual platelets are preferred for paper coating. Extremely thin, small
platelets with ragged edges produce a plastic clay for ceramic use. The latter
grades are often blended with larger well-ordered crystals ^2 JA) in order to
combine plastic strength with shrink resistance (Lyons and Bowman 1973,
p.28). Loss of platy habit common in grains larger than 2fx makes these grains
unsuitable for paper coating.
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