What is clay?
Most people probably don’t think much about clay unless they are trying to grow a garden in it (mud is four parts sand to one part clay). But A.G. Cairns-Smith thinks a lot about clay and has devoted a chapter in his “Seven Clues to the Origin of Life” (University of Cambridge, 1985, chapter 11, pp. 80-88) to it. “On the grandest scale,” he writes, “in terms of sheer throughput of materials, the whole Earth is a continuous crystalliser for clay minerals.” (p.
Clay is a special kind of earth which is made by the decomposition of rocks through the action of weathering. What does that mean? Well basically, over time, bits of earth are carried from one place to another by water and deposited in areas where the water slows down to a trickle. (Have you ever gone digging by the water’s edge only to grab a handful of muck? Well that muck is clay.) As the bits of earth travel with the water, they pick up all sorts of stuff and by the time we pick up a box of clay from the pottery store, the muck has been collected and prepared for us to use. All of the tiny rocks and lumps have been removed and some additional materials, like sand are sometimes added to create the perfect workable clay. What Else? Clay can be found anywhere but it is only useful for pottery if it has good “plasticity.” You can test this by seeing how stretchy a piece of clay is. If you can take a piece of clay, roll it into a coil and bend it into a ring without cracking and falling
