Volcanic soils

Halloysite is an aluminosilicate clay mineral with the empirical formula Al2Si2O5(OH)4. Its main constituents are oxygen (55.78%), silicon (21.76%), aluminium (20.90%), and hydrogen (1.56%). It is a member of the kaolinite group. Halloysite typically forms by hydrothermal alteration of alumino-silicate minerals. It can occur intermixed with dickite, kaolinite, montmorillonite and other clay minerals. X-ray diffraction studies are required for positive identification. It was first described in 1826, and subsequently named after, the Belgian geologist Omalius d'Halloy.

Allophane is an amorphous to poorly crystalline hydrous aluminium silicate clay mineraloid. Its chemical formula is Al2O3·(SiO2)1.3-2·(2.5-3)H2O. Since it has short-range atomic order, it is a mineraloid, rather than a mineral, and can be identified by its distinctive infrared spectrum and its X-ray diffraction pattern. It was first described in 1816 in Gräfenthal, Thuringia, Germany. Allophane is a weathering or hydrothermal alteration product of volcanic glass and feldspars and sometimes has a composition similar to kaolinite but generally has a molar ratio of Al:Si = 2. It typically forms u

Andosols are soils found in volcanic areas formed in volcanic tephra. In some cases Andosols can also be found outside active volcanic areas. Andosols cover an estimated 1–2% of Earth's ice-free land surface. Andosols are a Reference Soil Group of the World Reference Base for Soil Resources (WRB). They are closely related to other types of soils such as Vitrosols, Vitrandosols, Vitrons and Pumice Soils that are used in different soil classification systems. The name comes from Japanese ( 'dark') and ( 'soil'), synonymous with (). In the USDA soil taxonomy (ST), many Andosols belong to the orde

upright=1.6|thumb|Andisols of the world upright=1.6|thumb|Many Andisols develop in the immediate vicinity of volcanoes

Imogolite is an aluminium silicate clay mineral with the chemical formula . It occurs in soils formed from volcanic ash and was first described in 1962 for an occurrence in Uemura, Kumamoto prefecture, Kyushu Region, Japan. Its name originates from the Japanese word , which refers to the brownish yellow soil derived from volcanic ash. It occurs together with allophane, quartz, cristobalite, gibbsite, vermiculite and limonite.