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Amorphous Mineral Colloids of Soils of the Pacific Region and Adjacent Areas'

YOSHINORI KANEHIR02 and LYNN D. WHITIIG 3

THE PRESENCE of amorphous mineral colloids have pointed out that the amorphous consti ­ in soils and geologic formations is not as un­ tuents make up a sizeable fraction in many soils common as was first believed in the early years occurring in Hawaii, Japan, New Zealand, Ore­ following the acceptance of the mineral gon, and other Pacific areas. These amorphous concept. In the early reports the occurrence of mineral colloids play a prominent role in soil amorphous material was associated with only a formation and also impart certain distinctive few rare and isolated clay materials. Because and unique properties to the soil. Thus, a re­ amorphous colloids are not the major component view of this nature appears justified. in most soils and their presence may be found in relatively low concentrations, if found at all, NOMENCLATURE OF AMORPHOUS COLLOIDS their detection has been difficult. Moreover, whereas crystalline clay minerals are relatively The isolation and description of amorphous -uniform in composition, the amorphous mate­ colloids have been difficult because of the great rials exhibit a varying degree of composition variability in materials. Moreover; early sam­ and poor degree of crystallinity, further adding ples classified as "amorphous" were actually to the difficulty in their identification. Often found to be finely crystalline with modern X-ray their presence has been suggested only because diffraction methods. Stromeyer and Hausmann mineral allocations of crystalline materials failed first used the name allophane to describe amor­ to add up to 100 per cent. In recent years im­ phous material lining cavities in marl in 1816. provement in the use of techniques such as Since that time many related materials have X-ray diffraction, infrared absorption, electron been called allophane and this term has become microscopy, and surface area determination, has associated with amorphous constituents of clay. made it possible to make significant progress in Ross and Kerr (1934) described allophane as the study of amorphous colloids. essentially an amorphous solid solution of silica, Much of the research dealing with amorphous alumina, and water having no definite atomic mineral colloids in soils has been conducted by structure, and they applied the term allophane soil scientists working in the Pacific region or to a great number of amorphous clay materials in its adjacent areas. The leadership in this field regardless of their composition. They studied definitely belongs to this group of researchers. five specimens of allophane, all essentially hy­ It is the object of this paper to review and drous aluminum silicates, and found that Si0 discuss the contributions of these workers in 2 ranged from 25 to 34 per cent, Ah03 from 30 order to obtain a better perspective of this very to 36 per cent, and H from 31 to 38 per important fraction of soils. These investigators 20 cent. The New Zealand workers (Fieldes et al., 1952, 1954; Birrell and Gradwell, 1956) have 1 This paper is based on part of a joint report by _members of the Clay Mineralogy Work Group of the used the term amorphous colloidal hydrous ox­ Western Soil and Water Research Committee. Manu­ ides apart from the term allophane in their script received October 3, 1960. description of amorphous clays. With allophane, 2 Department of Agronomy and Soil Science, Uni­ which is considered to be one of the most im­ versity of Hawaii, Honolulu. 3 Department of Soils and Plant Nutrition, Univer­ portant amorphous minerals, Fieldes (1955, sity of California, Davis, California. 1956) has preferred to recognize three distinct

477 478 PACIFIC SCIENCE, Vol. XV, July 1961 forms : allophane A, allophane B, and the in­ two hydrol humic Iatosols from the island of termediate form, allophane AB. In classifying Hawaii. The authors noted that the allophane the clay minerals Grim ( 1953) has included found in the subsoil of one of these soils was only the allophane group under the amorphous very similar to allophane from Woolwich, Eng­ clay minerals. Brown (1955) in his proposed land (Kerr, 1951 ) . and goethite were nomenclature has divided the amorphous min ­ reported to make up the bulk of the remaining erals into oxides, silicates, and phosphates. In clay fraction. They also investigated the low this system, allophane is included in the silicates. humic latosols and reported that the dominant minerals are of the kaolin family. Up to 10 per cent allophane was found to occur in the OCCURRENCE OF AMORPHOUS COLLOIDS clay fraction of this group of soils. Kelley and Page (1943) in their mineralog­ In a subsequent paper (1955) the same ical investigation encountered two soils from authors reported on a humic ferruginous late­ Naalehu and South Point on the island of Ha­ sol from the island of Maui which showed that waii that exhibited very high cation exchange almost 30 per cent of the clay fraction in the capacities, 120 m.e. and 88 m.e. per 100 g., subsoil was composed of allophane. respectively. They reported that differential The occurrence of allophane in some soils of thermal analysis showed pronounced endother­ northwestern Oregon was suggested by Whittig mic peaks at 160 0 C. for these two soils in et at. (1957). These soils, members of the addition to showing weak X-ray diffraction pat­ Cascade and Powell series, contained relatively terns. These inxestigators, therefore, concluded high percentages of alkali-soluble silica and that the high cation exchange properties were alumina. The amorphous alumino-silicate, in related to the presence of considerable amor­ these soils was formed by of aeolian. ' phous material. Included in this study were volcanic ash. soils from Vale, Oregon, and the Mojave Desert, In earlier work, Whittig (1954 ) reported which also gave very indistinct X-ray lines and the occurrence of a more stable form of allo­ showed low temperature breaks , inferring the phanein two 'humic ferruginous latosols of Ha­ presence of amorphous material. waii. The allophane of ' these soils had a rela­ Dean ( 1947) in his D.T.A. study of a num­ tively low cation exchange capacity (of the ber of Hawaiian soils derived from ash and order of 10 m.e. per 100 g.) and resisted solu­ lava found that many of these soils contained ' tion in boiling Na2C03 solution. . almost no crystalline clay minerals. In addition More recently Bates (1961) described the some showed almost no hydrous oxides. It was presence of mineral gels in Hawaiian soils which previously shown by Ayres (1943) that some are mixtures of aluminum, iron, silica, and ti­ of these same soils possess very high inorganic tanium compounds. The gel material is very cation exchange capacities. Dean concluded that reactive chemically and gives rise to inorganic it was possible that some of these soils contain and organomineral complexes in the colloid alterations of the kaolin minerals. fraction. Tanada (1950) divided Hawaiian soils into Matsusaka and Sherman (1960) have re­ five groups on the basis of chemical analyses ported that the iron hydroxide and oxide of the and dehydration studies . He obtained similar amorphous mineral colloid fraction of Hawai­ high cation exchange capacity values for the ian lateritic soils will form strongly magnetic two soils, Naalehu and South Point, that Kelley iron oxides on dehydration. This may help ex­ and Page (1943) had previously reported. How­ plain the magnetic properties of weathered ever, Tanada did not draw any conclusions re­ ferruginous geological formations. garding the cause of such high values. In Japan Sudo ( 1954) , Sudo and Ossaka Tamura, Jackson, and Sherman ( 1953) em­ ( 1952), and Aomine and Yoshinaga (1955) ployed X-ray, chemical, thermal, and infrared have pointed to allophane as the dominant con­ techniques and found up to 30 per cent allo­ stituent of Ando soils which are formed from phane in the less than 0.2 micron fraction of volcanic ash. These soils are characterized by a Amorphous Mineral Colloids-KANEHIRO and WHITIIG low bulk density, a high organic carbon con­ ( 1951 ) offered confirmatory evidence by ab­ tent, and low base saturation. These properties sorption spectra that allophane is not a mixture are attributed to the preponderance of allo­ of alumina and silica. phane. The Ando soils and related types are Tamura et at. ( 1953) assigned allophane to found associated with the Pacific ring of vol­ weathering stage 11 or the gibbsite stage in the canic activity. These Japanese workers have weathering sequence of clay-size minerals as found that the fine clay fraction of the Ando presented by Jackson et at. (1948 ). They noted soils is characterized by being amorphous to that the trend for increased gibbsite with in­ X-rays and possesses medium-to-high cation ex­ creased rainfall is very marked in passing from change capacities and high phosphate- and the low humic latosols to the hydrol humic ethylene glycol-retention values. latosols. With this increase in gibbsite is an The New Zealanders have also worked ex­ associated increase in allophane. tensively on the identification of amorphous con­ A mechanism for the transition of alumina stituents. In 1952 Birrell and Fieldes (1952) and silica through allophane to kaolin was pro­ and Birrell (1952) identified the presence of posed by Tamura and Jackson (1953). The amorphous material, principally allophane, in steps are as follows: (1) amorphous hydrous soils derived from rhyolitic and andesitic ash. alumina crystallizes to a gibbsite structure; (2) The allophane was found to be present mainly with partial dehydration, hydroxyls in the gibb­ in the clay fraction although it was inferred site octahedra are replaced by oxygens of the that it was present to some extent in the silt silica tetrahedra; (3 ) this process occurs in the fraction. These soils . were characterized by a presence of silica solutions and continues high water-holding capacity, high shrinkage, and through entrance of silica between gibbsite irreversible drying, characteristics that are strik­ sheets, resulting in a cross-linking of silicated ingly common to many other Pacific region soils octahedral sheets of alumina which corresponds dominated by allophane. Birrell ( 1952) also to allophane;(4) is formed from pointed our that these soils had a waxy appear­ allophane on completion of unidirectional bond ­ ance and were greasy to the feel, yet they were ing through alternate wetting and drying in an not unusually sticky. He further noted that as­ acid medium where enough silica is available. sociated with nonreversible drying, liquid and The stable, nonreactive form of allophane re­ plastic limit values were much greater for un­ ported by Whittig (1954 ) as a constituent of dried soils than for dried soils. some humic ferruginous larosols of Hawaii was Later reports, especially by Fieldes and his considered to be a weathering product of hal­ co-workers (1955, 1956, 1957, 1955), have con­ loysite. Electron micrographs of clay fractions firmed that allophane and other amorphous con­ of these soils revealed a transition from well­ stituents dominate many New Zealand soils de­ developed rod structures to spherical, rived from volcanic ash and, in some cases, X-amorphous allophane particles. It was sug­ basaltic parent materials. These workers urilized gested that partial removal of silica from the electron microscopy, differential thermal analy­ rigid halloysite rods by leaching allowed the sis, and infrared absorption extensively in iden­ rods to curl up in a direction perpendicular to tifying the presence of amorphous constituents. their original curvation. Allophane formed in this way possessed properties quite different from PEDOGENIC SIGNIFICANCE OF those of the more labile allophane described by AMORPHOUS COLLOIDS Tamura and Jackson (1953) and would occupy a lower position in the weathering sequence of Ross and Kerr (1934) described allophane Jackson et at. (1948 ). as an amorphous hydrous aluminosilicate having More recently Bates ( 1960 ) suggested that no definite chemical composition and that it is the development of allophane is a logical stage commonly associated with halloysite. They were in the weathering of certain Hawaiian volcanic careful to point our that it is not a microscopic ash and also in the matrix of rock. In other mixture of amorphous silica and alumina. Kerr cases, he indicated that allophane is an inter- 480 ' PACIFIC SCIENCE, Vol. XV, July 1961

mediate stage in the weathering sequence of In later papers Fieldes (1955, 1956, 1957) halloysite to gibbsite. Bates also reported the reported enough fundamental differences in allo­ formation of gibbsite crystals upon dehydration phane to warrant recognizing three types: allo­ of amorphous Fe-AI gels. This observation sup­ phane A, allophane B, and the intermediate POrtS Sherman (1957 ), who reported that crys­ type, allophane AB. Based mainly on infrared talline gibbsite aggregates formed when the absorption data, it was found that silica is linked soils of the Hydrol Humic Latosol group were with alumina to form allophane A while some air dried . These soils have a high content of silica is discrete as amorphous hydrous silica in amorphous mineral colloids which contain a sub­ allophane B. Fieldes could offer no satisfactory stantial amount of gel material. explanation as to why co-precipitation and link­ Some of the Japanese workers (Sudo, 1954; ing of alumina and silica occur to only a limited Sudo and Ossaka, 1952) conclude that allo­ extent in allophane B. He did not want to state phane precedes halloysite in the weathering that allophane B is simply a mixture of amor ­ sequence from ash to allophane to halloysite, phous alumina and silica. Differential thermal Aomine and Yoshinaga (1955) have also em­ analysis shows that a high temperature exo­ 0 0 phasized that the clay fraction of the volcanic therm between 850 and 1000 C. is strong in ash soils of Kyushu and Hokkaido formed un­ allophane A, not present in allophane B, and weakly developed in the intermediate form der similar well-drained cond i t ions is pre­ ~ dominantly allophane, regardless of differences allophane AB. Fieldes ( 1955) has presented in temperature, weathering time, vegetation, weathering sequence of clays derived from rhy­ and ash origin. olitic and andesitic ash: allophane B-allophane AB-allophane A-meta-halloysite-kaolinite. The New Zealanders have also tried to pro­ He has stated that in this sequence the stable perly position the amorphous materials in the form is rneta-halloysite and progress toward's · weathering sequence. Fieldes and Swindale this stable form through allophane A is consist­ ( 1954) have prepared it flow sheet tracing the mechanism of silicate minerals weathering. ent with the mechanism proposed by Tamura Th ey have proposed that the nature of the clay and Jackson ( 1953) . The structure consisting constituents of any soil can be predicted if its of hydrous alumina octahedra randomly cross­ parent material and weathering stage are known . linked by silica tetrahedra and called allophane The amorphous materials occupy a 'greac role by Tamura and Jackson would hence correspond in this flow sheet in that it is thought that the to allophane A as proposed by Fieldes. primary silicates (aside from the ) can­ There is a growing consensus among investi­ not form layer silicates without first passing gators in this field that amorphous colloids may through an amorphous stage. Clays derived from playa very important role in soil formation and rhyoliti c and andesitic ash pass through the in establishing properties of many soils of the weathering sequence from amorphous hydrous continental United States as well as in the Pacific oxides through allophane to meta-halloysite and islands. Because of their noncrystalline nature, kaolin. It is believed that many of the Hawaiian identification of allophane and other amorphous soils derived from andesitic ash follow this same constituents is at present very difficult, and at s eq~ence. best very unreliable, by standard meth ods of In an earlier paper Fieldes et at. ( 1952) em­ analysis unless they be present as pr edominant phasized that the amorphous hydrous oxides components of their system. In view of the fact played more than a brief transitory role. They that transition from primary silicates ( with the reported some soils of the lower Cook Islands exception of micas ) to the secondary layer sil­ which showed high cation exchange capacity icates must include some solution and reprecip­ values. These soils were all low in silica, and itation, it is reasonable to suspect that amor­ also allophane was not found to be a constitu­ phous colloids exist, at least as a transition stage, ent in them. They attributed the cation ex­ in most of our soils. The extent of their pres­ change capacity mainly to the amorphous hy­ ence is masked in most of our mineralogical drous oxides. studies by the crystalline components present. Amorphous Mineral Colloids-KANEHIRO and WHITIIG 481

The fact that amorphous colloids greatly affect properties of soils where they are dominant con­ REFERENCES stituents emphasizes the need for more critical examination of our soils for evidence of their AOMINE, S., and N. YOSHINAGA. 1955. Clay presence. According to Kanehiro and Sherman mine rals of some well-drained volcanic ash ( 1956), it is well established that allophane soils in Japan. Soil Sci. 79: 349-358. has low bulk density, high water-holding capac­ ity, and, in some cases at least, a high cation ex­ AYRES, A. S. 1943. Soils of the high rainfall change capacity. In addition it has been observed areas of the Hawaiian Islands. Haw aii Agr. that allophane has a strong aggregati on effect Expt. Sra, Tech. Bul. 1. on soils, a very high phosphate fixing capacity, BATES, T. F. 1960. Rock weathering and clay and the ability in some cases to fix organic com­ formation in Hawaii. Mineral Industries 29: pounds so as to render nitrogen available with 1, 4-6. difficulty to microorganisms and higher plants BIRRELL, K. S. 1952. Some physical properties (T. Sudo, private communication ) . of New Zealand volcanic ash soils. Proc. of Early researches of Burgess and McGeorge the First Australia-New Zealand Conf. on (1926) and Burgess (1929) in Arizona sug­ Soil Mech. and Foundation Eng. gested that amorphous alumina, silica, or alumi­ nosilicate may be formed quite readily in soils BIRRELL, K. S., and M. FIELDES. 1952. Allo­ by application of alkaline solutions. Kerr (1928) phan e in volcanic ash soils. Jour. of Soil Sci. furth er postulated that amorphous aluminosili­ 3: 156-166. cates may form even in slightly acid soils as a BIRRELL, K. S., and M. GRADWELL. 1956. Ion­ result of local hydrolysis of , solution of exchange phenomena in some soils containing alkaline silicates and aluminaresj-: and subse­ amorphous mineral constituents. Jour. of Soil quent co-precipitation. Sci. 7: 130- 147. Th e Pacific region and its adjacent areas, BROWN, G. 1955. Report of the clay minerals with their recent volcanic materials offer a group subcommittee on nomenclature of clay splendid opportunity for investigation of the minerals. O ay Min . Bu!. 2: 294-300. presence of, the properties imparted by, and the mechanisms of formation of, such amor­ BURGESS, P. S. 1929. The so-called "build-up" i n fl u~n c ed phous constituents in soils. and "break-down" of soil zeolites as by reaction. Arizona Agr. Exp. Sta, Tech. Bul. 28: 101-135. SUMMARY BURGESS, P. S., and W . T. MCGEORGE. 1926. The work on the amorphous mineral colloids Zeolite formation in soils. Science 64: 652­ of soils of the Pacific region and its nearby areas ()53. is described. DEAN, 1. A. 1947. Differential thermal analysis The amorphous colloids, especially allophane, of Hawaiian soils. Soil Sci. 63: 95-105. dominate the clay fracti on of many soils de­ FIELDES, M. 1955. Oay mineralogy of N ew Zea­ rived from volcanic ash, as well as some rocks, land soils, Part 2. Allophane and related min­ in the Pacific area. Soils dominated by these eral colloids. N. Z. Jour. of Sci. and Tech. 37: amorphous colloids have many distinct and 336-350. uniqu e properties. The position of the amor­ phous colloids, especially of allophane, in the --- 1956. Clay mineralogy of N ew Zealand weathering sequence remains to be fully clari­ soils, Part 3. Infrared absorption spectra of fied. soil clays.. N. Z. Jour. of Sci. and Tech. 38: For many reasons, the identification of amor­ 31- 43. phous colloids is often difficult; however, re­ --- 1957. Clay mineralogy of N ew Zealand cent improvements in instrumental techniques soils, Part 4. Differential thermal analysis. have greatly facilitated this ident ification. N. Z. Jour. of Sci. and Tech. 38: 533-5 70. 482 PACIFIC SCIENCE, Vol. XV , July 1961

FIELDES, M., and L. D . SWINDALE. 1954. Chem­ Ross, C. S., and P. F. KERR. 1934. Halloysite ical weathering of silicates in soil formation. and allophane. U.S. Geol. Surv. Prof. Paper N . Z. Jour. of Sci. and Tech. 36: 140-154. 185-G : 135-148. FIELDES, M., L. D. SWINDALE, and J. P. RICH­ SHERMAN, G. D . 1957. Formation of gibbsite ARDSON. 1952. Relation of colloidal hydrous aggregates in Iarosols developed on volcanic oxides ro the high cation- exchange capacity ash. Science 125 : 1243-1244. of some tropical soils of the Cook Islands. Soil STROMEYER, F., and J. F. L. HAUSMANN. 1816. Sci. 74: 197-205. Gorringische Gelehrte Anzeigen. 2: 125. FIELDES, M., and K. 1. WILLIAMSON. 1955. SUDO, T. 1954. Clay mineralogical aspects of Clay mineralogy of New Zealand soils, Part the alteration of volcanic glass in Japan. Clay 1. Electron micrography. N. Z. Jour. of Sci. Min . Bul. 2: 96-106. and Tech . 37: 314-335. SUDO, T., and J. OSSAKA. 1952. Hydrated hal­ GRIM, R. E. 1953. Clay mineralogy. McGraw­ loysite from Japan. Jap. Jour. of Geol. and Hill Book Co., Inc., New York. 384 pp . Geog. 22: 215-229. JACKSON, M. L., S. A. TYLER, A. L. WILLIS, G. TAMURA, T., and M. L. JACKSON. 1953. Struc­ A. BOURBEAU, and R. P. PENNINGTON. 1948. tural and energy relationships in the form a­ Weathering sequence of clay-size minerals in tion of iron and aluminum oxides, hydrox­ soils and sediments, 1. Fundamental general­ ides, and silicates. Science 117 : 381-383. izations. Jour. of Phys. and Colloid Chern. TAMURA, T.,l\t;:L JACKSON, and G. D. SHER­ 52: 1237-1260. MAN. 1953. Mineral content of low humic, KANEHIRO, Y., and G. D. SHERMAN. 1956. humic and hydrol humic latosols of Hawaii. Effect of dehydration-rehydration on cation Soil Sci. Soc. Amer. Proc. 17: 343-346. exchange capacity of Hawaiian soils. Soil --- 1955. Mineral content of a latosolic Sci. Soc. Amer. Proc. 20 : 341-344. brown forest soil and a humic ferruginous Iarosol of Hawaii. Soil Sci. Soc. Amer. Proc. : KELLEY, W. P., and J. B. PAGE. 1943. Criteria 19: 435-439. for the identification of the constituents of soil colloids. ' Soil Sci. Soc. Amer. Proc. 7: TANADA, T. 1950. Certain properties of the 175-181. inorganic colloidal fraction of Ha waiian soils. Jour. of Soil Sci. 2: 83-96. KERR, H. W. 1928. The nature of base exchange and soil acidity. Jour. Amer. Soc. Agron. 20 : WHITTIG, L. D. 1954. Crystalline and amor­ 309-335. phous weathering products in some soils of temperate and tropical origin. Thesis, Univ. KERR, P. F. 1951. Reference Clay Minerals. of Wisconsin Library. Amer. Pet. Inst, Proj . 49. Columbia Univer­ WHITTIG, L. D., V. J. KILMER, R. C. ROBERTS, sity, New York. and J. G. CADY. 1957. Characteristics and MATS USAKA, Y., and G. D. SHERMAN. 1961. genesis of Cascade and Powell soils of north­ Magnetism of iron oxide in Hawaiian soils. western Oregon. Soil Sci. Soc. Amer. Proc. 21: Soil Sci.: in press. 226-232.