It was explained that the clay is a pure mineral contained in a hot and dense rock, due to weathering then form fine particles and mostly moved by water power, wind and glaciers to a lower place and away from source rock with a particle size which is almost the same, while others remain at the location where the host rock is located. During the move, the clay becomes impure and lose minerals binder, the result is a type of clay ranging from coarse to fine with the possibility of a change of color and composition.
The nature of the event, then there is clay that does not move or remain in the region of origin, clay is called a primary clay which is the end result of a series of processes which are also called clay residue, examples of common clay is china clay or kaolin , While the clay is moved from the region of origin and settle in low areas called secondary clays or clay sediments, such as ballclay, red marls (a mixture of clay, sand, and lime), stoneware, and others.
Figure 8.Ilustrasi position of primary and secondary clay.
Clay is a mineral formed from the structure of the particles are very small, mainly of minerals called kaolinite, ie compounds of Oxide Alumina (Al2O3), with Oxide Silica (SiO2) and water (H2O). Size clay particles smaller than 2 microns (<0.002 mm) and shaped sheet / flat tiered and support each other in dry conditions and basah.Gambaran clay size compared to other materials is shown in Figure 8.
Figure 9. Comparison of the size of clay particles (clay), sand (sand) with a variety of sizes, and soil sediment (silt).
One of clay particles prepared by one molecule of alumina (2 atoms of aluminum and three oxygen atoms), two silicate molecules (two atoms silikadan two oxygen atoms), and two water molecules (two atoms of hydrogen and one oxygen atom). The formula consists of:
a) 39% alumina oxide
b) 47% silica oxide
c) 14% of water
Naturally changes which take place continuously cause the formation of primary and secondary clay, which also causes differences were found (precipitation) clay tersebut.Secara modest origins of clays can be described as shown below.
Figure 10. The origin of simple clay