Even though clay occurs in nature, you can use it mixed with a combination of materials to create a clay with specific properties in a recipe. These recipes give the clay certain properties that are useful for different ceramics.  Raku clay, for instance, is specifically designed to withstand the thermal shock, rapid expansion and contraction that clay bodies might go through when you pull it out of a red hot kiln into the ambient temperature. Other properties my be for looks only. Some clay bodies are kind of a buff color, some are a darker, orangy red color, and some like porcelain have a distinctive crisp, clean, white kind of color. Some clays are made to be turned on a wheel.They stand up very well to the manipulation that occurs when you compress and pull clay body up on the wheel to create large ceramic vessels. Other clays are used for hand molding. And then another type of clay is called slip. Slip is just a generic term for liquid clay.  These are poured into molds and fired to paint.  The two main types are stoneware and earthenware. The stoneware clays are generally high temperature clays. They're fired to, roughly, cone 10 which is approximately 2,400 degrees Fahrenheit, and earthenware clays, which are lower temperature clays which are fired to approximately 1,985 degrees which is around cone 04, cone 06. Different types of clay are formulated to be fired at different temperatures specified for the project you will be using them in.