How is clay made?

Clay has a wonderful plastic quality. When it is wet or damp we fan maid it and it keeps its shape after it dries out. If we bake it or fire it, the molded shape becomes even harder and also water tight. This trick was discovered before the dawn of history and all our ceramics and dishes are still made from clay,

There is a certain amount of clay in all good soil: This is why a very young person needs only a little water to make mud pies in any corner of the garden. It is possible to mold the mud because of the clay it contains. This moldable quality is because of certain chemical factors in the clay itself.

Under a microscope' we see that clay is made from very fine plate like particles.  It is made from two mineral compounds, silica and aluminia. Silica is a compound of the elements silicon and oxygen.  Aluminia is a compound of the elements aluminum and oxygen.

The plate like particles overlap and interlock with each other and the chemist tells us that they have a sticky quality. This is because each tiny particle can hold a film of water by electrical attraction. Each wears a thin slippery coat which makes it glide and slither among its neighbors. This is what makes clay plastic and why we are able to mold it. When heated, the moisture is driven out and the little plates lock together to form a firm solid. With greater heat, the little plates may weld together in a solid mass.

Clay is a by product of the ceaseless warfare between the rocks and the weather. Naturally, it can form only from rocks which contain the compounds silica and aluminia. The most common clay making rocks are feldspars and certain igneous or fire formed rocks such as granite and lavas.

Great boulders of these rocks look strong and solid indeed. But the weather and the changing seasons finally grind them to fragments. Rocks, like everything else, tend to expand with heat and shrink with the cold. The heat and frost of countless seasons tend to make them crack. Once a great boulder is cracked, the falling rain goes into action. It drips and trickles down, lapping at the sides of the cracks. Its greedy little tongues dissolve what chemicals it can, This weakens the rock.

The cracks widen, Large chunks break off and fall away and the relentless weather works to break them into still smaller pieces. It takes lots of running water to powder rocks into fine fragments of clay. For these little plate particles measure several thousands to an inch. At first, the new foamed clay may be a soft layer of mud. Later it may become buried and dried out into a layer of rocky shale. Still later it may be pressed into a brittle slab of slate.