Hematite as nature's pigment. Common in some soils because communication with the atmosphere produces an oxidizing environment. Other soils reducing. Students should be able to expand a bit on each of the below. Rephrasing the first question - how does rock turn into soil.
Effects diminish from the surface downward.
Below is a table from the same source showing some of the mineralogic changes. View of weathering pattern in a shallow Tertiary intrusive from the foot of the Chisos Mountains in Big Bend, Texas. Note the rectangular fracture pattern that outline weather blocks. The rock was originally all uniform in color and the banding represents oscillatory iron staining and reflects weathering that worked from the fracture margins into the interior of the blocks. The middle of the blocks are less weathered than the fracture margins.