What is kaolin?
Kaolinite is a mineral belonging to the group of aluminosilicates.
It is commonly referred to as "China Clay"
because it was first discovered at Kao-Lin, in China. The
term kaolin is used to describe a group of relatively
common clay minerals dominated by kaolinite and derived
primarily from the alteration of alkali feldspar and micas.
Kaolin is an industrial mineral used primarily as an inert
filler and customers combine it with other raw materials in
a wide variety of applications.
Kaolin is a white, soft, plastic clay mainly composed of
fine-grained plate-like particles. Kaolin is formed when the
anhydrous aluminium silicates which are found in feldsparrich
rocks, like granite, are altered by weathering or
hydrothermal processes. The process which converted the
hard granite into the soft matrix found in kaolin pits is
known as "kaolinisation". The quartz and mica of the granite
remain relatively unchanged whilst the feldspar is
transformed into kaolinite. Smectite may also form in small
quantities in some deposits. The refining and processing of
the fine fraction of the kaolinised granite yields
predominantly kaolinite with minor amounts of mica,
feldspar, traces of quartz and, depending on the origin,
organic substances and/or heavy minerals.
Individual kaolins vary in many physical aspects, which in
turn influence their end use. Of particular commercial
interest is the degree of crystallinity which influences the
brightness, whiteness, opacity, gloss, film strength, and
viscosity.