Mica must be present in initial parent material. Al concentration must be low or hydroxy interlayering will occur. Conditions may be more acid than with smectite. Clay mica - mica must be present in initial parent material. Moderate pH and concentrations of Si and Al.
Gives soil a yellow color.
Variable moisture conditions, but weathers to hematite under high oxidizing conditions. Hematite - Fe 2 O 3 . Gives soil a red color. Can form under variable moisture conditions but is favored under high oxidizing conditions. Found in poorly drained soil.