Articles

    It's Clay-Time

    Kids, so what do you know about "clay"? Clays are layered minerals found naturally in the ground. Often the layers are much too small to see, but sometimes the minerals crystallize in big enough pieces to see them by eye. Two examples are mica and vermiculite. Did you ever peel apart the shiny, thin, transparent layers from a piece of mica? Vermiculite is very similar to mica, and observing the layers is even made easier by the high pressure steam is that often used to expand this clay into fat, swollen chunks that feel cushion-y. Your parents and teachers may have heard of vermiculite as the gold-flecked mineral added to many potting soils. It makes an excellent insulation material, and is also used as a packing material due to it's absorbency and cushioning properties. Try to find a sample at a crafts store, a nursery, or a hardware store, and peel apart the layers yourself

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    It is between the layers or sheets of a clay that chemistry can take place. Many molecules are soaked up into these layers and are either strongly held or else react to form different molecules. Did you know that kitty litter is almost 100% clay? The absorbent properties of clays are obvious here, and they are especially good at binding up the smelliest molecules! Clays are sold commercially as products to help clean up spills, especially oily spills. You will come into contact with kaolinite clay many times a day, for it is used as both a paper filler and paper coating. In fact, the higher quality and glossier the paper is, the more kaolinite is coating the surface; and it aids in binding the inks and dyes. Kaolinite is also the active ingredient in Kaopectate®, and so clay is even used as a dietary aid

    Very pure clays can be used in a number of other products around the home. When all the iron and soil is removed, many pure clays are actually white. They are then ground into fine powders and added to many formulations. If you see "magnesium aluminum silicate" or "bentonite" or "talc" in the list of ingredients, then you know that some clay is there. It is an inert, harmless material and is used in lotions and sunscreens for example. So, besides your modeling clay and the clay in your lawn or gardens, take a look around your home and see how often you come across clays!

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    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    November 1996