Zonous Kaol ini te bea ring c lay de pos it is made by
hydrothermal alteration of volcanic rocks mainaly of andesite ami dacite.
Kao linit e , quartz and calci te are the main mineral co mposi tions. As
quart z in the volcanic roc ks is cryptocrys talline, it is too dificult to
seperat e it from kaol inite. The phys ical properties and chemica l
composition of Zonous ceramic grade kaolinite bearing clay are directly
related to its nature and geOlogical formation.
The percenl age of SiOz in Zonous clay is highe r but the amount of
Alz0 3 is lower th an Diamond kaolinte. For th is re ason the ceramic
products of zonous cl ays have lower resistance to thermal shocks and
modul e of rupture. High roughness, low plsticity and possible greater
deformation during firing (Production of Ceramics) are o ther reasons
for lim it ing the use of Zonous ceramic grade clays. The percentage of
calcium oxide (CaO) in Zo no us clay is higer in co mparison wi th
Diamond Kaolin hut pot asium oxide (KzO) whi ch plays as a nux in
ceramic products is lower in zonous. The high pereentage of CaO which
has a high melting point can raise the viscosity as a result lead to Crack
in ceramic products. Fin ally with these colour pro pe rties, the Zonous
ceramic grade kaolinite bearing clays , can be used as a fill er in pape r,
paint and rubber industries.