| Clay, an important raw material for several industries,
has been studied for a long time by geologists, ceramists
and soil chemists, and is one of the mineral raw materials
being used by man since pre-historic times. Clay may be
defined as a fine-grained rock, which becomes plastic,
when mixed with small quantities of water. In chemical
composition, it contains essentially silica, alumina and
water, and variable minor amounts of iron, alkalies
and alkaline earths. Mineralogically, it is characterized by
the presence of clay minerals and varying but subordinate
admixture of nonclay minerals comprising quartz,
felspar, calcite, flakes of mica, gibbsite, goethite, hematite,
titanium minerals, etc. In particle size, the clay
minerals are mostly concentrated in the size fraction of
two microns or less, while nonclay minerals are usually
absent in 1 to 2 micron fraction. |
