One of the most important factors is the type of rock from which the inorganic material in the soil
originated. The parent rock provides the soil with a great deal of the chemical back bone for the soil. For instance, a soil that contains sediment from limestone will be high in calcium, and will also have a basic pH. This will be much different than one that derives from granite, which will have a higher sodium or aluminum content and a pH that tends more toward neutral or acidic.