Andisols
Andisols (from Japanese ando(“黑土”)是在火山灰或其他火山喷出物中形成的土壤. 它们与其他阶的不同之处在于，它们通常以玻璃和近阶胶状风化产物(如allophane)为主, 铁长石和水合铁. As a result, 和二醇具有化学和物理特性，包括高保水能力和“固定”(使植物无法使用)大量磷的能力. 它们分为八个亚目:Aquands, Gelands, Cryands, Torrands, Xerands, Vitrands, Ustands and Udands.
Globally, 安土是最不广泛的土壤阶，只占无冰陆地面积的大约1%. 它们大约占1.7 percent of the U.S. 土地面积，包括太平洋西北地区一些非常多产的森林.
Andisols have andic soil properties in layers either: (1) with a cumulative thickness of 36 cm within 60 cm of the mineral soil surface; or (2) comprising at least 60 percent of the depth between the mineral soil surface and a root-restrictive horizon. (USDA-NRCS image)
