The central concept of Andisols is that of soils dominated
by short-range-order minerals. They include weakly weathered
soils with much volcanic glass as well as more strongly weathered
soils. Hence the content of volcanic glass is one of the
characteristics used in defining andic soil properties.
Materials with andic soil properties comprise 60 percent or
more of the thickness between the mineral soil surface or the
top of an organic layer with andic soil properties and a depth
of 60 cm or a root limiting layer if shallower.