I . 

Please do not destroy or throw away this publication. If you have no further use 

for it write to the Geological Survey at Wa~hington and ask fot a frank to return it 

U~ITED STATES DEPARTMENT OF,' THE INTERIOR 

Harold L. Ickes, Secretary 

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director 

Professional Paper 185---,-G 

HALLOYSITE AND ALLOPHANE 

BY 

CLARENCE S. ROSS 

ANQ 

PAUL F. KERR 

Shorter contributions to general geology, 1934.,...35 

(Pages 135-148) 

UNITED STATES 

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1934 

For sale by the Superintendent of Documents, Washington, D. C. - - - - - Price 5 cents 

' ( 
CONTENTS 

Page 

Abstract _____________ ________ ~------------------------- ----------------------------------------------------- 135 

Introduction _____________________ ~---------------------------------------------~----------------------------- 135 

IIalloysite___________________________________________________________________________________________________ 135 

Nomenclature ____ ~------- ---~----------------------------------------- ----------------------------------- 136 

Types ______________ ·--------------------------~---------------------------------------~----------------~ 136 

Chemical composition _____________________________________________________________________________________ • 136 

Optical properties_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 138 

I>ehydration_____________________________________________________________________________________________ 139 

JC-ray examination_______________________________________________________________________________________ 141 

Mode of occurrence ___ · _________________________ . ________________ .:. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 142 

Associated minerals___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 142 

Origin___________________________________________________________________________________________________ 143 

Residual halloysite _________________________ ,_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 143 

Action of acid-bearing solutions ___________________ ..,____ ___________________________________ _____________ 143 

Allophane___________________________________________________________________________________________________ 144 

Previous studies---------------------------------------~--------~----------------------------------------- 144 Chemical composition _________________________________________________________________ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 145 

Optical properties ___________________________________________________________________________________ ._____ 147 

ILLUSTRATIONS 

PLATE 28. A, JC-ray diffraction patterns of halloysite; B, JC-ray diffraction patterns of dickite and nacrite_ _ _ _ _ _ _ _ _ _ _ _ _ _ 140 

29. A, Photomicrograph of halloysite and alunite; B, Photomicrograph of porcelainJike indianaite_______________ 140 

FIGURE 6. I>ehydration curves of halloysite and related minerals _____ ·______________________________________________ 140 

7. I>iagram of JC-ray diffraction patterns of halloysite_____________________________________________________ 141 

8. I>ehydration curves of allophane_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ _ _ _ __ __ _ _ __ ____ _ _ _ _ _ _ _ _ _ _ _ _ _ 148 

II 
I 

I 

I . HALLOY~ITE A~D ALLOPHANE 

. , ABSTRACT . 

~'his paper is a continuation· of the study of the kaolin minerals, in the :first part of which, published. in· i9·31, the kaolin 

minerals kaolinite, dickite, and nacrite ·were described. -In 

that paper the application of chemical, optical, X-ray, and 

dehydration methods to the .investigation of clay materials 

were discussed. 

The present study shows that halloysite is a fourth II'Lineral 

of the kaolin :group, closely related to but distinct from 

kaolinite. · T'he chelnical, ti~al, X-r~y, ·and d~hydration 

properties of a representative group of halloysites are recorded, 

all these being new data determined by the authors mi separate portions of single samples whose p:urity has been·· carefully tested. 

Halloysite has been previously described as amorphous, because the microscope commonly reveals no evidence of crystal 

structure. X-ray· diffraction studies, however, show that ).t 

has a crysta~ structure, beil!-g made up of ·crystal gra~ns of 

submicroscopic size. The X-ray diffraction patterns of kaoli-. 

nite and halloysite have a number of lines in common, but' 

others are distinct and indicate that these are distinct 

minerals. 

Halloysite appears to be always the result of weathering, 

or supergene processes, like kaolinite but unlike dickite and 

nacrite, the other kaolin minerals, which are cominonly the 

result of hydrothermal processes. 

Allophane is an ;::tmorphous material that is commonly 

associated with halloysite. It has no crystal structure and 

no definite chemical composition. The name allophane should 

be restricted to mutual solutions of' silica, alumina, water, 

and minor amounts of bases but should include all such 

materials, even though the .proportions of these constituents 

may vary. · It is shown that perfectly homogeneous solutions 

of allophane and other amorphous materials may exist. Thus 

several occurrences described as " allophane" are found to 

be such mixtures o~ norm~l allophane and evansite, an amorphous hydrous aluminum phosphate. 

INTRODUCTION 

A study of the clay minerals has been in progress 

in the laboratories ·of the United States Geological 

Survey and Columbia University for several yearB. 

In an earlier paper 1 the minerals kaolinite, dickite, 

und nacrite we-re described. These studies have been 

continued, and the present paper sets forth the results. 

IIalloysite, like those earlier described, is a mineral of 

the kaolin grop.p. Allophane is related in mode of 

occurrence, ·although, being amorphous, it is quite 

different mineralogically. 

1 Ross, C. S., and ·Kerr, P. F., The kaolin minerals: U.S. Geol. Survey 

Prof. Paper 165, pp. 151-176, 1931. 

I 

. HALLOYSITE 

A . white or light-colored, approximately isotropic. 

clay mineral ·known as "halloysite" locally forms 

sm.aJl nearly pure niasses or is abundantly. associated 

with kaolinite in many kaolin deposits. The association, the chemical composition, the optical data, and 

the X-ray properties indicate its close relation to the 

minerals kaolinite, dickite, and nacrite of the kaolin 

group, but the 'present study shows that halloysite is 

~, distinct mineral. Not all nearly isotropic clay materials .are halloysite, for some prove to he very fine 

grained kaolinite, and others are clay material of a 

quite unrelated group. On ~he other hand, most iso-

: tropic clay materials with an index of refraction near 

that of qua.rtz are the definite clay mineral halloysite. 

rhe original halloysite was found in the Carboni£-

. erous limestone of Angleur, Liege, Belgium, in a district of o_ld zinc and iron mines. It was first de-

; scribed in 1826 by Berthier,2 and was named" halloy-

. site,. in honor of Omalius d'Halloy, who had observed 

the mineral several years previously. The mineral 

occurred in pockets containing alteration products and 

in solution cavities in the limestone: All the deposits 

are now exhausted, and it is impossible to obtain material from the old mine openings. Several specimens 

of halloysite from these deposits are, however, still on 

reserve in the collections of the University of Liege. 

Through the kindness of Prof. H. Buttgenbach, of the 

University of Liege, we have ~een able to procure a 

suite of specimens of this, material, which are probably 

as nearly representative of type halloysite as it is 

possible to obtain at the present time. 

These specimens have been reexamined and compared with halloysite from other localities. Halloysite_ 

has also been compared with the related kaolin minerals-kaolinite, anauxite, nacrite, and dickite-and 

with other clay minerals. The method of study employed in this work is described in the paper on the · 

kaolin group, already cited. All determinationsoptical properties, X-ray diffraction data, and chemical analyses-have been made on different fractions 

of the same ~ample. The chemical and optical studies 

have been carried on in the laboratories of the United 

2 Berthier, P., Analyse de I'halloysite: Annales chimie et phys., voJ. 

32, pp. 332~335, 1826. 

135 
136 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

States Geological Survey, and the X-ray studies have 

been conducted in the mineralogical laboratory of 

Columbia University. Both these organizations have 

cooperated in the preparation of this report. 

NOMENCLATURE 

Dana lists under halloysite 3 16 mineral names that 

he considers to be synonymous with it. Most of these 

names were proposed before 1850, the original materials were poorly described, and analyses were made 

on material of doubtful purity. Obviously most of 

such materials are not available for restudy, and under 

such circumstances a detailed consideration of these 

names, most of which have fallen into complete disuse, 

would serve no useful purpose. However, a few of 

these may be briefly mentioned. 

The only name that has been consistently applied to 

the clay mineral here considered is "halloysite ", 

which was proposed 108 years ago. Fortunately, 

therefore, there is no question of the name that should 

be retained. 

. Smectite has been considered to be at least in part 

halloysite,4 but recent studies by Kerr 5 have shown 

that the clay material of representative samples is 

montmorillonite, the typical clay mineral of normal 

bentonites. 

The name " indianaite " was proposed by Cox 6 in 

187 4 for a white porcelainlike clay in the Carboniferous rocks of Lawrence County, Ind. The studies of 

indianaite given in the present paper (p. 143) show 

that it is a rock composed of impure halloysite. Cox 

seems to have recognized that "indianaite" was not 

· the name of a mineral but was to be used as a rock 

r.ame, for he says,7 "This large bed of white clay to 

·which I have given the name of 'indianaite' (Indiana 

stone)." 

Collyrite (collyrium) was discussed by Dioscorides 8 

and by Pliny,9 but the character of their material is 

doubtful. Analyses by the Gladstones 1'

0 indicated 

that material from Hove, near Brighton, was a 

hydrous aluminum oxide with accessory clay material 

giving a ·small but variable amount of silica. Optical 

and X-ray examinations of a sample of so-called 

" collyrite " from the Fichtelgebirge show that this 

8 Dana, E. S., Descriptive mineralogy, 6th ed., p. 68, 1909. 4 Kirwin, Richard, Elements of mineralogy, 2d ed., vol. 1, p. 184, 

1794. Hatiy, R. J ., Traite de mineralogie, vol. 4, p. 444, 1801. 

Breithaupt, August, Handbuch der Mineralogie, vol. 2, p. 544, 1844;. 

Thomson, Thomas, Outlines of mineralogy, geology, and mineral 

analysis, vol. 1, p. 246, 1836. 5 Kerr, P. F ., Montmorillonite or smectite as constituents of bentonite : Am. Mineraiogist, vol. 17; pp. 192-198, 1932. 6 .Cox, E. T., Indiana Geol. Survey 5th Ann. Rept., for 1873, p. 15, 

Indianapolis, 187 4. 7 Cox, E. T., Indiana Geol. Survey 7th Ann. Rept., for 1875, p. 154, 

Indianapolis, 1876. 8 Dioscorides, Pedacius, Materia medica, book 5, p. 151, 50 A.D. 9 Plinius, Caius, Historia naturalis, book 35, p. 16, 77 A.D. 10 Gladstone, J. H. and G., On collyrite and a native carbonate of 

alumina and lime : Philos. Mag., vol. 23, pp. 461-466, 1862. 

material is kaolinite. It therefore seem)S probable 

that the name "collyrite" represents no definite mineral and should be dropped by mineralogists, although 

it would be desirable to retain· a name that goes back 

to the time of Pliny if the material to which it was 

applied could be definitely identified. 

Lenzenite was first described by John 11 from Kall, 

in Eifel, and the examination of material from this 

locality (though not definitely type material) shows 

that it is dominantly kaolinite. 

Galapectite from Anglar, France, the type locality,u is montmorillonite, as shown by the optical 

properties. X-ray diffraction patterns of galapectite 

also agree with patterns of the type montmorillonite. 

"Bole" (bolus) was a term applied to clay materials which found an application in medicine and whose 

use goes back to times of antiquity. Obviously the 

name was used for materials of varying character, but 

more recently it has been applied to earthy, nearly 

amorphous clay materials colored brown, red, or yellow by iron oxides. Some of these have been identified 

as impure halloysite. 

TYPES 

In general there are two types of halloysite-one 

. that is usually white or light-colored, porous, friable, 

or almost cottony in texture; and another that is dense, 

nonporous, and porcelainlike. The reason for this 

difference has not been determined, for the optical, 

chemical, and X-ray properties appear to be identical. 

The colors of the porcelain-like material are white, 

light gray, buff, or faun for the purer types, and 

brownish or reddish for those containing iron oxides. 

The white or nearly white halloysite assoda.ted with 

kaolin deposits (commonly those of the residual type) 

. is difficult to distinguish from very fine grained kaolinite, and both types of material may be associated with 

the coarser-grained, obviously crystalline kaolinite. 

HaUoysite does not appear to be an abundant constituent of sedimentary beds, although it may result 

from the local alteration of such beds. Kaolinite appears to be much more abundant and in regions of 

profound weathering forms extensive deposits, but 

even kaolinite forms but a small fraction of the clay 

· material of sedimentary rocks. Some of the clays 

similar to montmorillonite or beidellite and a sedimentary alkali-bearing clay mineral are much more 

abundant. . . CHEMICAL COMPOSITION 

Analyses have been made on 12 samples of halloysite 

from widely separated localities. Standard analytical 

methods were used and need no discussion. · 

11 John, J. F., Chemische Untersuchungen: Chern. Schrift., vol. 5, 

p. 193, 1816. . 12 Breithaupt, J. F. A., Vollstandige Charakteristik des MineralSystems, 3d ed., p. 99, 1$32. 
HALLOYSITE AND ALLOPHANE 137 

With materials as fine grained as most halloysites 

it is not possible to apply any treatment to remove inlpurities. For . that reason nearly all the samples 

analyzed represent material that occurs naturally jn 

a perfectly homogeneous and apparently pure condition. Only one sample, that from Franklin, N.C., was 

washed and decanted to remove associated kaolinite 

and muscovite. 

The following table gives the results of the chemical 

analyses. This table and the table on page 138, which 

gives the optical properties, are so ar:r;anged that the 

numbers in the two tables apply to the same samples. 

For this reason no. 1 is omit~d in the subjoined table, 

as no chemical analysis is a.vailable. A detailed description of the specimen is given in connection with 

the table on page 138. 

Chemical anal~ses of halloysite 

2 3 4 . 5 6 7 8 9 10 11 12 13 

Si 02 _ - -- ____ - _ 44. 75 40. 26 43. 67 44. 34 44.08 44. 08 41. 62 44. 68 44. 50 39. 84 44. 18 43. 10 

Ab03---------- 36. 94 37.95 37:91 37.39 39. 20 38. 60 38. 66 38.59 38. 68 39. 70 39. 34 40. 10 

Fe203- ________ . 31 . 30 0 26 . 42 . 10 0 32 . 62 0 39 0 24 0 64 0 32 0 64 

FeO _____ ---- _ (a) (a) -------- -------- None -------- -------- -------- -------- ----.-14- -------- -------- MgO __________ (a) (a) (b) . 04 0 05 . 22 . 08 0 08 . 05 . 03 . 20 

CaO _____ - - _ - _ .11 0 22 -------- . 17 None 0 12 . 10 0 18 None 0 40 . 30 0 24 

N a20 __ - ----- -

} 0 60 . 74 -------- { 0 17 } 0 20 (c) { .11 1. 19 } (c) (c) K20- - - ------- . 04 -------- . 05 . 14 -------- P20s---------- -------- -------- . 12 -------- ------·-- -------- -------- -------- -------- -------- -------- -------- H20--------- 2. 53 4.45 3. 79 2. 00. 1. 44 2. 34 4. 26 1. 55 1. 17 1. 76 . 96 1. 08 

H20 +--.:.----- 14.89 15. 94 14.50 15.09 14. 7·1 14. 72 14.64 14.90 14.38 17.52 14. 96 14.82 

100. 13 99. 86 1_QO. 25 99. 66 99.81 100. 40 99. 98 100. 53 100. 35 100.00 100. 09 100. 18. Ratio of Si02: 

Al203-- __ --- 206:100 180:100 195:100 201:100 191:100 189:100 177:100 196:100 195:100 171:100 165:100 180:100 

a Doubtful. b Trace. • Not determined. 

2. Liege, Belgium. Analyst, L. T. Richardson. 

3, 4. Huron County, Ind. Analyst, L. T. Richardson. 

5. Peppers, N.C. Analyst, E. T. Erickson. 

6. Hickory, N.C. Analyst, J. G. Fairchild. 

7. Hickory, N.C. Analyst, F. A. Gonyer. 

8. Adams County, Ohio. Analyst, F. A. Gonyer. 

The silica-alumina ratios in the halloysites represented in the preceding table range from 206:100 to 

165: 100. Six samples have a ratio between 191: 100 

and 206: 1.00 and an average of 197: 100 or close to 

2 :1. The other six san1ples show a ratio between 

165: 100 and 189:100, and an average of 177:100. 

The average for the entire group of analyses is 

187: 100. The generally accepted ratio for halloysite 

is AlzOs: Si02 : H 20= 1: 2: 2.13 

The rather large and systematic deviation of the 

silica-alumina ratio from the ratio 2:1 in so large a 

number of apparently pure samples demands consid~ 

eration. The alumina is a little higher than the accepted ratio in n1ost of the samples, and this suggests 

at first that they may have contained a slight excess · 

of some aluminous mineral. However, optical and Xray studies prove that they contained practically no 

crystalline impurities, and the only possible explanation would be the presence of noncrystalline material. 

Such a material forming an amorphous matrix around 

crystalline grains would be expected to cause induration of the material. However, the compact, porcelainlike samples approach more nearly the ideal con1~ 

13 LeChatelier, H., De l'action de Ia chaleur sur Ies argiles : Soc. 

fran~aise mineralogie Bull., voi. 10, pp. 204- 211, 1887. 

9. Brandon, Rankin County, Miss. Analyst, Charles Milton. 

10. Leakey, Real County, Tex. Analyst, R. K. Bailey. 

11. Sneeds Creek, Newton County, Ark. Analyst, F. A. Gonyer. 

12. Franklin, N.C. Analyst, F. A. Conyer. 

13. Myeline, Saxony. Analyst, F. A. Gonyer. 

position than those with a friable chalky texture. The 

average ratio of 8 · poreelainlike samples is 191: 100; 

that of the chalky samples is 179: 100. 

A comparison of the analyses of halloysite with 

those of kaolinite 14 indicates that halloysite tends to 

be riyher in alumina than kaolinite~that is, kaolinite 

tends to be somewhat closer to the ideal formula 

2HzO.Al20s.2Si02 than halloysite, although anauxite, 

the high-silica end member of the anauxite-kaoli~ite 

group, has a silica ratio of 3: 1. Taking the anauxitekaolinite series and halloysite together, we have a 

variation in the silica-alumina ratio from 294: 100 to 

165:100. The sample from Franklin, N.C., with the 

ratio 165 : 100, corresponds closely with the ratio 3: 2, · 

·which has been assigned to pholerite,15 a crystallized 

clay mineral described by Guillemin 16 in 1825. This 

formed hexagonal plates and so probably · belongs to 

the kaolinite series. However, a member with this 

ratio seems probable and might belong to either the 

anauxite-kaolinite or the halloysite series, and the high 

alumina in many samples of halloysit€ makes it seem 

14 Ross, C. S., and Kerr, P. F., op. cit., p. 163. 15 Ries, Heinrich, Clays ; their occurrence, properties, and uses, 3d 

ed., p. 81, New York, John Wiley & Sons, 1927. 

1e Guillemin, J., Note sur Ia phol~rite: Annales des mines, vol. 11, 

p. 489, 1825. 
138 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

probable that such a molecule :forms part o£ a 

halloysite series. 

Consideration of the variable silica-alumina ratio 

in carefully selected and analyzed kaolinite and anauxite led to the conclusion that this was probably 

.not due to impurities but was the result of a truly 

variable ratio between the two end members/7 the 

valence requirements being satisfied by a variation in 

~he number of the hydrogen atoms. I:f this_ is so, the 

material with the lower silica would liave the higher 

water content. ·This inference is partly confirmed by 

the :fact that the wf,tter ratio is distinctly higher in the 

analyses with a silica-alumina ratio below 180: 100 

than in those Ill which the ratio is between 191: 100 

and 206: 100. 

OPTICAL PROPERTIES 

17 Ross, C. S., and Kerr, P. F., op. cit., p. 165. 

The optical properties of 20 samples of halloysite 

.are given in the :following table: 

Optical and physical properties of halloysite 

No. Locality Name ·· Texture Color 

1 Liege, Belgium ______ , __ Halloysite _____ Porcelainlike_ Pale blue ___ _ 

2 _____ do--------------~- ---do __ ----- _____ do ______ White ___ -- '- 3 Huron, Lawrence "Indianaite" _______ do ___________ do _____ _ 

County, Ind. 4 _____ do ___________ . __________ do _____________ dq------ Pale buff ___ _ 

5 Peppers, Mitchell 

County, N.C. 

Halloysite ________ .:._do ______ White ______ _ 

6 Hickory, Catawba _____ do ________ Chalky ___________ do _____ _ 

County, N.C. 7 _____ do _____________________ ao _____________ do ________ .:. do _____ _ 

8 Adams County, Ohio ________ do________ Porcelainlike_ Pale buff ___ _ 

9 Bradon, Rankin County, _____ d,a _____________ do ______ White __ • ___ ·_ 

Miss. 

10 Leakey, Real County; _____ do~--- ---- ChalkY--- -- _____ do _____ _ Tex. '· 

11 Sneeds Creek, Newton "Newtonite" ____ .;. __ do_.; _________ do _____ _ 

County, Ark. · 12 Franklin, N.C _________ "Kaolin"----- _____ do ___________ do _____ _ 

13 Myeline, Rochlitz, Sax:- "Lithomarge" _ .Porcelainlike_ ----do _____ _ ony. 

14 Bergnersruth, Bavaria __ "Glagerite" -~- _____ do ______ 'cream _____ _ 

15 Maid en, C a ta wb a Halloysite_____ Chalky ______ White ____ :. __ · 

County, N.C. 

16 Hillsboro, · Highland _____ do ________ Porcelainlike_ :Light gray __ _ 

County, Ohio. · 17 Hart County, Ky ___________ do ________ Chalky ______ -----do _____ _ 18 Cordillera of Peru ___________ do ________ Porcelainlike_ Light faun __ _ 

19 Alban, Tarn, France -- :.. _____ do ________ Compae,t ____ Dark red ___ _ 

20 Rolla, Phelps County, "Flint clay" ________ do ______ Nearly white_ 

Mo. 

21 Lookout, Ala __________ Halloysite _____ Porcelainlike_ Gray _______ _ 

22 Fichtelgebirge, Bavaria_ "Collyrite" ____ Compact ____ Palefaun ___ _ 

23 Saszka Bunat, Hun- "Lithomarge" ______ do ___________ do _____ _ 

gary. 

Index' or refract~on 1;3irefringence Remarks 

1. 552 None_ _ _ _ Type locality. . Associated 

with alunite, allophane, 

gibbsite. 1. 546 Slight_ __ :. D6. 

1. 546 ___ do_____ Type locality. Very clean 

material. 

1. 552 None ____ Associated with phosphate 

mineral. 

1. 551 Slight ____ Small flattened nodules 

coated with ferruginous clay . . 1. 552 ___ do _____ }Contains a little mica and 

quartz. Derived from 

1. 551 None :. _·__ pegmatite. 

1. 550 Slight_ ___ Variable in character, . but 

best lumps very pure. L 548. ___ do _____ . Very pure material. 

1. 559 ___ do _____ 'Some specimens ~ontain ~1- , • unite." . . . 

1. 552- ...: __ do_ "'..:__ Halloysite and 'alunite: Type 

locality. 

1. 556 None____ Admixed with kaolinite and 

1. 558 ·Slight ____ 

1. 552 _ __ do _____ 

1. 591 ___ do ___ . __ 

1. 543 ___ do _____ 

. 1. 561 ___ do _____ 

1. 552 None ____ 

f. 648 ___ do ___ "'/-. 

1. 567 ___ do _____ 

1. 555 ___ do _____ 

a little residual muscovite. 

Botryoidal masse~ coated 

with iron-stained halloy- site. . · Drusy cavities contain kaolinite. 

Contains a trace of mica 

and quartz. Derived from 

pegmatite. 

Associated with an impure ferruginous clay . Contains some alunite. : Very pure. 

Shows sedimentary bedding planes and contains iron 

oxide. 

Contains some kaolinite. 

Do. 

1. 558 __ .:.do _____ Botryoidal surfaces, com- pact core. 1. 554 ___ do'----- Botryoidal surfaces. 

1, 2. From Angleur, Liege, Belgium. No. 1 is light sky-blue, 

and no. 2 is nearly pure white. It forms small irregular ironstained .lumps, . but by hand picking pure clean material was 

selected. Porcelainlike in texture and shows conchoidal fracture. Occurs in limestone in the vicinity of iron and zinc 

mines. 

oxide, which were completely removed by hand picking. Occurs at the contact between Chester shales (Mississippian) 

and the Mansfield sandstone (Pennsylvanian) .

18 

3, 4. Pure white; with conchoidal fracture. The outer surfaces are iron-stained, and small cavities contain manganese 

5. Forms small irregular lenses 2 centimeters or more across 

in a region of altered igneous and metamorphic rocks. The 

18 Logan, W. N., Economic geology of Indiana: Indiana Dept. Conservation Pub. 21, p. 672, 1922. 
HALLOYSITE AND ALLOPHANE 139 

outer coating is iron-stained, but the material is pure white 

below the surface. It has conchoidal fracture. 

6, 7. Friable, with an almost talcose feel. 

8. Conchoidal fracture. Dr. Walter Bucher, who collected 

the material, has kindly supplied the following description of 

its occurrence : 19 

"White fragments of halloysite occur in nearly circular 

areas at three places near the borders of the cryptovoleanic 

area in Adams and Highland Counties, Ohio. In one locality 

a gully has cut into the mass, showing that the pure halloysite 

is only a few inches in thickness and grades downward into a 

mixture of halloysite and clay where it fills pores of fragments that are residual after dolomite. Traces of halloysite 

form rather widely distributed _ iron-stained gray masses of 

clayey material, which occur along the contact of the black 

Ohio shale with the underlying Silurian dolomites. Commonly only isolated fragments are seen, which appear waxy 

when taken fresh-ly from the ground. Upon drying these 

crack into the familiar white or light-colored an,gular fragments, which take _a high polish when rubbed." 

9. One mile east of Bradon, Miss. Irregular nodules, with 

an iron-stained coating. 

10. Six miles w_est of , Leak~y, Tex., in the_ Edwards 

Plateau region. The following description of the occurrence 

has been supplied by Dr. R. F. Ryan, of the Vacuum Oil Co., 

Houston, Te~. : 20 1 

"The material has been penetrated to a depth of 130 feet 

in one shaft and has been found to occur over an area of approximately 320 acres. The formations which outcrop arounp. 

this deposit are Edwards limestone, Comanchean age, Fredericksburg d~vision. The material iies below the limeston1~, 

but a siliceous mass associated with the kaolinitic material 

contains chei;t fragments." Most of the samples from thts 

locaUty are very fine-grained kaolmite, but a few are very 

pure halloysite. 

11. Halloy~ite (originally described as newtonite 21 ). The 

occurrence arid location given below are taken from a description by Wherty.22 : • 

" The locality is situated in the Harrison quadrangle, about 

4 miles west of Compton in the gorge of Sneed's Creek. The 

material was collected from a group of small prospect pits in 

decomposed ~hale which carried small lumps of -soft white 

chalky material, more or 'less stained' by iron oxides." 

After chemical and optical studies, Foshag 23 concluded that 

in the original study by Brackett and Williams the optical 

determinations had been made on alunite and the analysis on 

halloysite. ' 

12. Halloysite, about 4 miles north of Franklin, N.C., where 

it forms an isotropic matrix around tiny kaolinite crystals 

in a kaolin deposit resulting from the weathering of a peg·-

matite. Hallhysite separated from kaolinite by washing. 

13. Halloysite (" kaolinite"). Occurs in irregular ironstained lumps a few centimeters in diameter. 

14. Halloysite. Dense material, containing a few i:cregular 

cavities with chalky-white CDatings. · 

15. Creamy-white, soft mass. 

16. Light-gray porcelainlike masses. 

17. Light-gray chalky masses. 

10 Personal communication. 20 Personal communication. See also- Ries, Heinrich, The clays tOf 

Texas : Texas Univ. Bull. 102, Sci. ser., vol. 2, pp. 82-84, 1908. 21 Brackett, R. N., and Williams, J. F., Newtonite and recto-rite, 

two new minerals o-f the kaolinite group: Am. Jour. - Sci., 3d ser., 

vol. 42, pp. 11-21, 18!}1. 22 Wherry, E. T., A visit to the locality of newtonite : Am. Mineralogist, vol. 10, pp. 350-351, 1925. 23 Foshag, W. F., The identity of newtonite with alunite: Am. 

Mineralogist, vol. 11, pp. 33-35, 1926. 

18. Exact locality unknown. 

19. Soft material that contains m,uch iron oxide. The Xray diffraction pattern of this sample is weak, even for a 

pattern of halloysite, and suggests th~ presence of elements 

having higher absorption for X-rays. Mixed hydrous iron 

oxide could account for the unusually high inde;x: o;f refraction. 

20. Associated with diaspore. 

21. Conchoidal fracture. 

22, 23. Relations unknown. 

It is possible to determine, only one index of refraction of halloysite, because much of the material 

is completely isotropic, and the remainder has a birefringence of 0.001 or less. The ·cause of this faint 

birefringence is not entirely clear. Some of it may be 

due ~o very slight strain, but it seems probable that 

a very fine mottled gray effect just within the powers 

of resolution of the microscope is 'a real birefringence 

due to a partly oriented aggregate of birefracting 

mineral grains of submicroscopic size. The X-ray 

studies. described on ·page 141' show that halloysite 

is truly crystalline and closely related to other minerals of the kaolin gToup. As it is so closely related 

to these minerals it is probably not isotropic and so 

has a birefringence t4at is usually not observable bec~use the unoriented grains are smaller than the 

powers of resolution of the .microscope. However, all 

the other members of the kaolin group have a birefringence of about 0.006 to 0.007, and it seems probable 

that two minerals so closely related in chemical composition, mean index of refraction, and character of 

space lattice as kaolinite and halloysite would have 

approximately the same birefringence. 

The optical properties of halloysites given in the 

table show some variation. The index of refraction 

of no. 19, from Alban, France, is abnormally high, 

owing to the presence of iron oxide, but the 22 others 

show a variation between 1.543 and 1.567, and 11 of 

these have indices between 1.551 and 1.556. The mean 

of the entire series is 1.5527. The variation is due, in 

part at least, to the variation in water content, discussed on page 140. The average for the {3 index 

of refraction of 16 samples of kaolinite 24 is 1.5647, 

showing that kaolin averages 0.012 higher · than halloysite in index of refraction. This is due, at least in 

part, to the higher water content of halloysite but is 

probably due in part to inherent crystallographic 

differences. 

DEHYDRATION 

Dehydration tests have been made on three typical 

samples of halloysite. Two of these-one from Adams 

County, Ohio, and one from Liege, Belgium-were of 

the dense, porcelainlike type, and the other, from 

Hickory, N.C., was of the chalky type. The Hickory 

sample has a lower total water content than the other 

two, but the analyses given in the table on page 137 

24 Ross, C. S., and Kerr, P. F., op. cit., p. 162. 
140 SE:ORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

indicate that this difference is not a characteristic of 

the group as a whole. 

Curves plotted from this table and from data on 

kaolinite from lone, Calif.; dickite· from Cusihuiriachic, Chihuahua, Mexico; and nacrite from Brand, 

Saxony,25 are given in figure 6. 

Dehydration temperatures of halloysite · 

Ohio Belgium North Carolina The dehydration curves of halloysite show that 

there is a very gradual loss of water up to a temperature of about 400° to 430° C., where there is a break 

in the curves, and a rapid loss of water up to a temperature of about 500°, after which there is a rapid 

flattening of the curve. The dehydration curves tend 

to flatten at 200°, but if this has any real significance 

the reason is not apparent. It is quite evident that the 

water lost up to 110° ( 1.44 to 4.75 percent) is not 

significant but represents adsorbed water. In fact the 

water lost up to 200° (2.5. to 5.20 percent) is no doubt 

adsorbed. 

Temperature 

oc. 

105 

150 

240 

300 

350 

375 

410 

450 

485 

525 

560 

600 

650 

700 

Ignition 

Loss of water 

Percent 

4. 72 

5. 10 

5. 20 

5. 37 

6.00 

6.03 

6. 40 

14. 23 

15.82 

17. 42 

17.70 

17.86 

18. 16 

18. 53 

19. 13 

}-

z 

w 

22 

20 

18 

16 

u 14 

0:: 

w 

0. 

z 

12 !t 

w 

1-

~ 

510 

LL. 

0 

(f) 

(f) 

3 8 

6 

Tempera- ture 

oc. 

Room 

55 

135 

145 

240 

260 

340 

390 

435 

475 

515 

555 

620 

740 

850 

I 

4 

v; 

v 

Loss of water 

Percent 

0. 00 

2. 60 

3.83 

4.39 

4.67 

4.92 

5. 82 

5. 56 

7. 12 

14. 02 

18. 91 

19. 53 

20. 17 

20. 78 

21. 10 

• 

r. -"" 

~ 

Tempera- ture 

oc. 

110 

160 

200 

250 

300 

350 

400 

450 

500 

550 

600 

650 

700 

800 

--------

Loss of water 

Percent 

1. 44 

1. 47 

2. 10 

2. 54 

2.68 

2. 98 

3.86 

6. 72 

14. 32 

15. 32 

15. 52 

16. 01 

16. 18 

16. 22 

It is to be expected that material made up of submicroscopically crystalline ,particles would have a 

--------- 2s Ross, C. S., and Kerr, P. F., op. cit., p. 166. 

~ L---e--- Hallo~site 

Liege, elgium 

I~ ~ 

Halloysite 

:tldams County, 

~ Ohio 

i 

I~ Halloysi· e 

..... - Hickory,~ 

A v ~ 

~ Nacrite 

Brand, Saxony 

Dickite, Me-xico 

1/j ~ Kaolinite 

/1 7 lone, Calif. 

'j f( 1/ 

~ 

/ '/ 

I 

£ lJ ~ v 

/I 

~ L/ lp 2 

~ ~ 

/ ) ""'0" 

~ ~ 

100 0 

200 0 300 0 0 0 400 500 600 0 700 0 BOO" 

TEMPERATURE 

FIGURE 6.-Dehydration curves of halloysite and related kaolin mtnerals. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 28 

Halloys.lte (white) 

Liege, Belgium 

Halloysite 

Adams Co., Ohio 

Hal loy site 

Cor-dillera of Peru 

Halloysite 

Nevada 

Halloysite and alunite 

Edwards Plateau,Tex. 

Alunite 

Japan 

A. X-HAY DIFFRACTION PATTERNS OF HALLOYSITE F'HOM SEVERAL LOCALITIES. 

A pattern of halloysite mixed with alunite is also shown, and a pat'tern of alunite for comparison. 

Dickite 

Greenwood, Ark. 

Halloysite (white) 

Liege, Belgium 

Kaolinite 

Brooklyn, N.Y. 

B. X-RAY DIFFRACTION PATTERNS OF DICKITE AND KAOLINITE COMPARED WITH HALLOYSITE. 

The dotted line indicated near the zero beam for dickite and kaolinite was masked by the shield of the casette. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 29 

A. PHOTOMICROGRAPH OF HALLOYSITE AND ALUNITE FROM VICINITY OF HURON, IND. 

The nearly isotropic areas are halloysite, and the intermediate finely crystalline material is alunite. Crossed nicols, 'X a,bout 27. 

B. PHOTOMICROGRAPH OF PORCELAINLIKE INDIANAITE SHOWING HALLOYSITE WITH SHATTER CRACKS FILLED WITH ALUNITE. 

The halloysite mass contains small spherulitic areas, which, to judge from the X-ray lines, are gibbsite. Crossed riicols, X about 27. 
HALLOYS;J:TE AND ALLOPHANE 141 

rather large content of adsorbed water and that part 

of this should be held rather tenaciously. The very 

perfectly crystalline dickite, on the other hand, loses 

no water at 110° and only' 0.12 percent up to 450°. 

The essential, high-temperature water of halloysite is 

evidently that lost between 400° (or perhaps 250°) 

and complete dehydration. It is interesting to note 

that X-ray diffraction patterns of samples used for 

dehydration show a loss of lines between 450° and 

500° C. It appears, therefore, that the break in the 

curve is accompanied by a loss of crystallinity. 

The dehydration curves for the other minerals of 

the kaolin group--:-kaolinite, dickite, and nacrite-indicate a distinctly higher temperature stability than 

that of halloysite. The lower break in the curves of 

kaolinite and nacrite, where a distinct loss of water 

begins, is at about 490°, and for dickite at about 510°. 

That is, halloysite begins to break down at 60° to 80° 

lower temperature than the other minerals of the 

kaolin group. 

C\i::::; "' "'-""> ~ ~ It) 

~'< '1- 0)(0 ") ~ '<;f '? f'j <\i (\j -...: 

l I~ .. .:. 

;::: ~!; ~; 

~ ~ t 

{ ; 

· ~ i ~ :~! ~ ~ i ~~ 

4 /0 5 6 4 5 4 

l n !". 

~ I ~ ~ 

The region between 4 and 3.4 angstrom units is most 

critical with :molybdenum radiation, in distinguishing 

between halloysite and kaolinite. Three broad and 

diffused lines occur in this portion of the pattern of 

halloysite, whereas five sharper lines occur in the same 

region in the pattern ·of kaolinite. · The comparative 

interplanar spacings and estimated relative intensities 

of the _two patterns for this region are as follows: 

Comparative interplanar spacings of halloysite and kaolinite 

Halloysite Kaolinite i 

-

Estimated . Spacing (ang- Estimated Spacing (ang- relative relative 

intensity strom units) intensity strom units) 

10 4.42 10 4.464 

5 I ·3. 97 10 4. 194 

6 3. 63 5 3. 874 

6 3. 614 

5 3. 424 

/nterp!anbr spacing 

Halloysite, normal o/pe 

10 22 Estimated intensity 

~~ ·~ 

H.. Ha/loysite, Liege, Be!givm 

!;j 

FIGURE 7.-X-ray diffraction pattern of halloysite. Lines 4 and 5 have a t~mdency to be merged together in the more firmly crystalline 

halloysite. 

X-RAY EXAMINATION 

X-ray diffraction patterns of halloysite given in 

plate 28, A, typify a pattern due to finely divided 

crystalline material of colloidal dimensions. The diffraction lines are not sharp, like those of well-crystallized minerals, but have diffused borders, and many 

of the intervening spaces are darkened somewhat by 

general radiation. In general about 10 distinct lines 

appear that can be measured with fair accuracy. 

Other lines are usually too weak to be measured accurately. A diagram illustrating the arrangement of the 

diffraction lines and their corresponding interplanar 

spacing is shown in figure 7. 

The X-ray diffraction patterns of halloysite are 

related to those of kaolinite. Diffra.ction lines at 1.560, 

2.365, 1.685, 1.510, 1.295, and 1.250 angstrom units 

agree in intensity and spacing with lines in the X-ray 

diffraction pattern of kaolinite. A single isolated line 

at 7.42 angstrom units occurs in the X-ray diffraction 

patterns of both minerals and likewise in those of 

nacrite, dickite, and anauxite, and this line is apparently significant for the kaolin group. 

P~tterns of kaolinite and halloysite given in plate 

28, B, also show differences with both iron and copper 

radiation. Dr. Stirling B. Hendricks, of the Fixed 

Nitrogen Research Laboratory, United States Department of .Agri·c:ulture, has taken photographs illustrating this diffe: ence with a copper target and has furnished negatives for our comparison. Dr. E. R. Jette, 

of the department of 1nining and metallurgy, Columbia University, has furnished us with X-ray diffraction photographs using iron radiation. The iron and 

copper radiations, paticula.rly when the [3 lines of 

the K series as well as the a lines are photographed, 

show mb·re E)triking · differences than are normally 

observed when the K- a radiation of molybdenum 

is utilized. In view of these differences in X-ray 

diffraction, which imply a fundamental difference in 

crystallization, it appears that halloysite should be 

distinguished from the other members of, the kaolin 

group. · Thus, the X-ray patterns confirm the difference between kaolinite and halloysite noted in the 

optical examination and dehydration curves. 

A system oj[ diffused X-ray diffraction lines, such as 

is observed in ha1loysite, is to be expected in a mineral 
142 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

that is optically almost isotropic. On the other hand, 

as kaolinite is obviously crystalline and doubly refracting with the polarizing microscope, the X-ray 

diffraction lines should be the lines of a well-crystallized mineral. It is also to be noted that the mean 

index of refraction of kaolinite is appro-ximately 

1.565, while the index of refraction of halloysite is 

approximately 1.553. Thus the lack of agreement in 

refractive indices indicates a difference between the 

two minerals. The distinct. difference in temperature 

stability between halloysite and the other kaolin 

minerals is probably more significant than the observa.ble optical properties and tends to confirm the Xray diffraction data in indicating a distinct mineral. 

X-ray diffraction patterns of halloysite from Liege 

differ from patterns of glassy allophane, which occurs 

'in the same locality. The glassy allophane forms an 

indistinct X-ray diffraction pattern that consists of 

three are·as of broad diffused radiation. The areas of 

diffused radiation, however, do not correspond to 

groups of lines in the halloysite pattern. Thus it does 

not appear that allophane is simply a finer state of 

subdivision of the crystal particles of halloysite but 

is a distinct species. 

As pointed out in the foregoing discussion, differences in X-ray patterns also indicate that halloysite. 

is not merely a finely divided kaolinite. All the sam~ 

ples of halloysite examined, however, have been composed of very finely d~vided m,aterial, and it has not 

yet been determined ·whether a more coarsely crystalline compound would crystallize as halloysite or would 

form kaolinite~ Experience thus· far indicates that the 

more coarsely crystalline material is kaolinite, or 

anauxite. · 

As a result of optical studies, halloysite has been 

consiq.ered an amorphous mineral by Rogers,26 who 

calls it the amorphous equivalent of kaolinite. X-ray 

data would indicate, however, that. the mineral has 

definitely discontinuous vectorial properties, one of the 

considerations emphasized by RQgers in distinguishing 

amorph~us minerals; hence it should not properly be 

called amorphous. It should be pointed out, on the 

other hand, that halloysite occupies a state of crystallinity intermediate betw~en the microcrystalline particles of kaolinite and . the finely .. divided, almost 

completely dispersed allophane. Wherry 27 has proposed the grouping of minerals into crystals, meta-. 

colloids, and colloids. Halloysite probably . belongs to 

the colloidal group of W,herry 8 .. considered with 

reference to particle size. 

26 Rogers, A. F., A review of the amorphous minerals: Jour. Geology, 

vol 2~ ~ 555, 191~ · 

zr Wherry, E. T., Variations in the compositions 'Of minerals: Washington Acad. Sci. Jour., vol. 4, p. 112, 1914. 28 Wherry, E. T., A tabulation of the aluminum silicate minerals: 

Am. Mineralogist, vol. 10, no. 6, p. 143, 1925. 

Measurements of the X-ray diffraction pattern of halloysite from 

Liege, Belgium 

No. 

Arc (milli- Estimated Interplanar Line no. meters) relative spacing (ang- intensity strom units) 

. 1 ___ ---------·- 11. 0 4 7.42 

2-------- ---- 18. 5 10 4. 42 3 _____________ 20. 6 5 3. 97 4 _____________ 22. 5 6 3. 63 5 _______ , ______ 32. 0 4 2. 560 6 _____________ 34.7 5 2. 365 7 _____________ 48.8 . 4 1. 685 8 ___ :_ _________ 54.7 10 1. 510 9::.. ____________ 63. 8 2 1. 295 10 ____________ 66.4 2 1. 250 

Record of X-ray diffraction patterns 

Locality 

. 

Minerals present in clay as shown 

by X-ray patterns 

1, 2 . Liege, Belgium ________ -.- ____ Ha:lloysite plus allophane, 

3,4 

5 

6, 7 

8 

10 

11 

Huron, Lawrence Comity, 

Ind. 

gibbsite, alunite. 

Do. · 

Peppers, Mitchell County, Halloysite. 

N.C. 

Hickory, Catawba County, Halloysite plus kaolinite. 

N.C. 

Adams County, Ohio ________ Halloysite. 

Leakey, Real County, Tex.: a 

Isotropic_______________ Do. 

Partly isotropic ____ _. ____ Halloysite plus alunite. 

Sneeds Creek, Newton Coun- Do. 

ty, Ark, ("newtonite"). 13. Rochlitz, Saxony a ("litho- . Halloysite. 

14 

16 

17 

18 

19 . 20 

21 

marge"). 

Bergnersruth, Bavaria a(" glagerite"). Hillsboro, Ohio ____________ _ Hart County, Ky __________ _ Cordillera of Peru __________ _ Alb~n, Tarn~ France .b _ ., ____ _ 

Rolla, Mo. a (flint clay)' ______ _ Lookout, a Ala ______________ _ 

Do. 

Do. 

Halloysite plus alunite. 

Halloysite. 

Do. · Halloysite plus kaolinite. 

Do. 

a Halloysite from these localities contains impurities visible with a microscope but 

causing no apparent effect on the X-ray pattern. 1> Contains visible iron oxide. 

. MODE 0~ OCCURRENCE 

Halloysite is very commonly associated with kaolinite in some kaolin deposits, especially in residual deposits derived from pegmatite. Here the relations of 

the two minerals indicate that the first clay mineral 

to form , is ·commonly halloysite and that kaolinite is 

the result of its recrystallization. · Halloysite also occurs together with allophane in some deposits in such 

a way as to indicate that it has resulted from the 

crystallization of that mineral, although it is improb-

; able that all halloysite lias formed in this manner. 

: Other . specimens form _ lenslike masses in fract~res in 

: rock, suggesting that the halloysite has been precipi-

' tated; from solution. 

ASSOCIATED MINERALS 

Alunite has been found associated with halloysite, 

. studied in the preparation of this report, in specimens 
HALLOYSITE AND ALLOPHANE 143 

:from five · localities-'-Liege, Belgium; Lawrence 

-County, Ind.'; Newton County, Ark. (pl. 29, A); Hart : 

County, Ky.; and Leakey, Real County, Tex . . It probably also occurs along with halloysite elsewhere. In ; 

each . o:f the five localities mentioned specimens may . 

be obtained in which alunite is intimately mixed with i 

halloysite as a fine-grained mixture, but halloysite ; 

free from alunite also. occurs in each locality. The ; 

halloysite :free :from alunite is dense, usually resem- : 

-bling porcelain in appearance (pl. 29, B), and ap- : 

pears· almost isotropic in thin sections. 'White masses : 

from· Indiana ·or the vicinity of Liege contain con.- : 

traction cracks along which finely. crystalline alunite \ 

and kaolinite · have penetrated, filling the· cracks: ln · j 

·such occurrences it appears that ·the finely crystalline : 

mixture represents a slight~ later phase in the ; 

process of formation of the white clay, although prob-

-ably not separat'ed :by a cessation. D:f chemical· action. 

· Allophane, discussed on page 144, , is associated 

with halloysite near Liege, where l:t occurs as a clear 

hyaline mass with black streaks of carbonaceous stains, 

and material of similar chara.cte'r occurs with halloysite at Huron,Ind. . . . . 

Diaspore is !1 com.mon 'associate of halloysjte in tl}e 

flint clays of Missouri. Exc.ellent .. ~:..ray;· diffraction 

·pattern§': of thi~ mineral, P,ave been· obtained ~rom_ ma.-

terial ·associated, witli flint clay from the c9ffim~rc~a~ 

clepp~its ~f Gasc,onade County. '' ~- ~. - ~ .. ' 

- GibBsite has been fo).:nid'in association wjth· halloy= 

site in the speci~ens £r¢IT:t ~iege: . ·' An x--ray diffr~ction pattern-- of purified material agrees with X-ray 

patterns of gibbsite from ~everal localities. · Gibbsite 

has also been identified in association with indianaite 

by K-rays. , ~ ·· · · ·. · · 1 , • • 

·The association of diaspore and gibbsite · with halloy$ite nder ~ert~irr ~ircu~stan~es may acccH~_.~t :for 

some of the variations in chemical analyses. · ·It· 1s alsg 

further evid~nce in support of the origin of halloysite 

a~ a result af wea~hering. - . ' 

'·'·oRIGIN 

Halloysite appears to be the result o:f supergene 

processes; so far as known it. never forms as a resu_lt 

of hypogene hydrothermal processes, like dickite and 

nacrite, two of the other kaolin minerals. Like . kaoljnite, it :forms through weathering and by the· action 

of cool sulphate-bearing solutions on aluminous. materials. 29 Weathering is clearly the dominant source oi 

kaolinite and probably of halloysite, bu,t a conside:r;-

able· proportion of hallo;y.site has been formed in areas 

where oxidizing sulphides have supplied sulph~ric 

acid. . --

Residual · halloysite.-The specimens o:f halloysite 

from ·Franklin and Hickory, N.C., are probably typical ?f halloysite in the residual white clays ·in the 

211 Ross, C. S., and Kerr, P. F., op. cit., pp. 172-174. 

southeastern United · States. Bayley 30 has described 

the occurrence of the residual white clays in the 

vicinity of Franklin. He states : 31 · 

The kaolins of North Ca~olina have without doubt peen 

formed directly or indirectly by the weathering of feldspathic 

rocks. Those in, the mountain regions, where the surface 

waters have had almost direct access to the material o~ ~he 

pegmatite dikes, have been formed directly by weathering. 

The kaolins around Bessemer City, Bostick's 'Mills, and 

Statesville ·may have been form~d somewhat differently. 

There the areas underiain by the · clay are wide rather tban 

long and narrow, as in the mountain district~ · an,d possibly 

the feldspathic rocks,from which the kaolin has been derive(! 

were formerly covered. by swampy tracts, sq that the · surface 

water p2rcolating through them _to the. bedrock be~ame ~liarged 

with carbonic and ·Organic acids, Which not Oiily accelerated 

the process of weathering 'but may" have caused the remov~~ 

of s'ome iron that was in the parent rock. · .~ . ,· ·_. , · 

Ries 32 . h~s. giyen a revi~w .of. the_ ~v]A~nce·"_for prqfound leach~ng aJ,Id weatheri.ng of the,· :vhit~ ~aoli!ls 0~ 

the soutl;:teasterTI,· Unitecl States. , As halloysite occurs 

mixed ' with kaolinite, in>~uch deposit~, the two. m.in~ 

eral~ 'arE?' ,probably dhe . to .·the same caus.e. 'It is s~~­

gested, •however,· tha~ halloysite oc?u·rring u?-der $Uch 

eonditions may, r,epresent a sta:ge ~;h the eventua1 .. crys~ 

tallization oi kaolinite. A simila·r origin observed ·in 

a white kl;t.olinite ,clay from Brookiyn·

33 point~ t() 'the 

:formatio'n of ccdloidaJ m.aterial in some loc~lities ptiqr 

to the cry~tallizat oti o:f kaolinite. . . , ) 

At · R~lla, Mo., profound le~chip.g has prod_hced 

diaspore sutrou;qded by zop,es ·o:f .flint · clay. · Sor.rLe , o:f 

the material• from these deposits . is .called '~burley 

~lay" a1,1d is 'co:rhposed ?f krtotlike masses o:f djasp?r~ 

in flint clay that is inade. up dom:in~ntly .of hall<):fSlte; 

Th~ . typical flint cl.ays lying outside the zone" of ~ur ley 

cl:;ty contain a 1arg~r: proportiou of halloysite bu~ 

appear to be not entirely pur:e, and their mineralogy 

an,d paragenesis d~serve detailed stu<Iy:.. . . _ .· 

Action-of acfd-beaiinq soZutions.~Ries ];).as pointe~ 

out that the so-called " iudian:aite " near Huron, in 

the so~thw .. est corner o:f Lawrence County, Ind,., is not 

a distinct mineral species but a mixture o:f fine-grained 

minerals including halloysite. 34 The studies· here_ recorded show that the white porcelainlike material is 

commonly some'}Vhat. impure halioysite, but selected 

samples of w~ry pure halloysite were obtained through 

the courtesy o:f Mr. George Whitlach, of India,na University. . . _ 

The origin of the white clay in Indiana has been 

studied by Ries,35 who conc}udes "that _the wh_ite clay 

3o Bayley, w. s., High-grade clays of the eastern .United States-: U.S. 

Geol. Survey Bull. 708, p. 41, 1921. · ' · 

31 Idem; p. 20. 

. 32 Ries, Heinrich, Origin of ·white residual kaolins: Am. Cera~ic 

Soc. Trans., vol. 13, pp. 51-74, 1911. · ' , · . . . 

aa Kerr, P. F., Kaolinite from il Brooklyn subway tunnel : Am. Mmeralogist, vol. 15, pp. 144-158, 1930. 

34 Ries, Heinrich, High-grade clays of the eastern United States: 

U.S. Geol. Survey Bull. 708, p~ 156, 1921. 

as Idem, pp. 159~162 . 
144 . SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

was formed by the replacement of the quartz pebbles 

of Pottsville sandstone, at least where the clay occurs 

in that formation." . Ries expresses the opinion that 

~• the pyrite of the Chester shales would by contact 

with underground water be decomposed and yield sulphuric acid, which would attack the alumina of the 

shales and form aluminum sulphate." A good path 

is present for circulating waters to follow, and it is 

thought by Ries that the aluminum sulphate solution 

replaces the quartz, forming halloysite and related 

1ninerals. This theory follows rather closely one previously advanced by Logan,36 who proposed a biochemical origin for indianaite. He postulated thereplacement of the sandstone by halloysite and presented 

n series of illustrations pointing out that origin. 

Logan, however, attributed the formation of halloysite to both the action of sulphuric acid solutions 

forming aluminum sulphate and to bacterial action, 

which precipitated the clay from the sulphate solutions when in contact with quartz. Bucher 37 pointed 

out certain weaknesses in Logan's theory, and Ries in· 

his studies of indianaite did not accept it. The three 

writers agree in assigning an important role to sulrhuriy acid caused by the decomposition of iron sulphide and point to the action of meteoric waters as 

causing the solution, circulation, and deposition of the 

clay .from the shale, but on the whole it seems quite 

unnecessary to postulate the action of bacteria in the 

formation of halloysite. 

The association of alunite with halloysite as previously described is another evidence of the action of 

sulphate-bearing solutions in the formation of kaolinitic clays. Alunite was first detected in accounting 

for extra lines in an X-ray diffraction pattern of indianaite. Alunite is generally believed to form by 

precipitation from solutions carrying H 2S04 ,

38 and the 

presence of this mineral in association with halloysite 

would tend to support the theory of replacement by 

sulphate-bearing solutions in the Indiana occurrence. 

The halloysite (" newtonite ") locality in Newton 

County, Ark., is marked by prospect pits in a lead and 

zinc mining region. In this region oxidized zinc ores 

have resulted from the oxidation of sulphides, and it 

seems evident that the alunite and probably the halloysite have formed by the action on shales of waters 

containing sulphuric acid. 

The halloysite from Liege, Belgium, is known to 

come from a region of old zinc mines, and its association with alunite makes ·it seem probable that sul36 Logan, W. N., A biochemical theory of the origin of indianaite : 

Science, new ser., vol. 49, p, 197, 1919; Kaolin of Indiana: Indiana 

Dept. Conservation, Div. Geology, Pub. 6, pp. 35-76, 1919. 37 Bucher, W. H., Logan's explanation of the origin of Indiana's 

"kaolin": . Econ .. Geology, vol. 16, no. 7, pp. 481-492, 1921. 88 Cross, Whitman, Alunite deposits of Rosita Hills, ColoO.: U.S. Geol. 

Survey Bull. 511, pp. 3&:-43, 1912. Ransome, F. L., The geology and 

ore deposits of Goldfield, Nev.: U.S. Geol. Survey Prof. Paper 66, 

pp. 189-195, 1909. 

phuric acid solutions have played a part in producing 

the halloysite of that region. The description of hal- · 

loysite furnished by Bucher (see p. 139) shows that 

oxidizing pyrite has been effective in producing t~at . 

material in the Ohio region, and the same origin may 

probably be . ascribed to the material from Hart 

·county, Ky. · 

The deposits near Leakey, Tex., have not been 

studied in the field, but the association of halloysite 

with alunite and the presence of abundant diss~mi:­

nated flakes of hematite show that sulphur and iron 

bearing materials were present and oxidizing processes 

have been active. There is every reason to believe that 

the Leakey deposits were formed during the oxidation 

of pyrite and the action of the resulting acid-bearing 

solutions on the shales. 

It therefore seems probable that the halloysite in 

at least six of the localities from which material considered in this paper was obtained was the result of 

the action of waters containing sulphuric acid. 

ALLOPHANE 

A clay mineral commonly associated with halloysite 

that may be considered in this paper is allophane. 

This material is of amorphous, commonly glassy character and variable composition. It forms incrustations; thin seams alternating with halloysite, as at 

Liege, Belgium; or rarely stalactitic masses. The 

purest material is clear and colorless, with a hyalitelike appearance, but may be blue, pale green, brown, 

or yellow. 

PREVIOUS STUDIES 

A.llophane and related materials have been described 

under various names. It was observed by Riemann in 

1809, at Griifenthal, near Saalfield, ·in Thuringia, 

where it lines cavities in marl, and was named "allophane" by Stromeyer and Hausmann, in 1816.39 The 

name" riemannite" was applied to material from the 

same locality by Breithaupt 40 the following year. 

Sack described " elhuyarit " 41 from the brown coal of 

E'riesdorf, near Bonn. Carolathine, a material similar 

to allophane but lower in water, was described by 

Sonnenschein,42 from Zabrze, near Gleiwitz, in upper 

Silesia. 

In 1850 Dana 43 described samoit, which has since 

been listed under allophane. Optical examination of 

material from the same locality in the Roebling col39 Stromeyer, F., and Hausmann, J. F. L., Gottinglsche Gelehrte 

Anzeigen, vol. 2, p. 125, 1816. 40 Breithaupt, A., in Hoffmann, C. A. S., Handbuch der Mineralogie, 

vol. 4, p. 182, 1817. 41 Sack, A. L., Scohweigger's Jour. Chemie u. Phys., vol. 65, p. 116, 

1832. 

42 Sonnenschein, F. L., Ueber das Carolathin: Deutsch. geol. Gesell. 

Zeitschr., vol. . 5, pp 223-226, 1853. 

43 Dana, J. D., System of mineralogy, 3d ed., p. 288, 1850. Dana, E. 

S., idem, 6th ed., p. 693. 
HALLOYSITE AND ALLOPHANE 145 

lection of the United States National Museum shows 

that it is not amorphous but crystalline and is probably montmorillonite rather than allophane. 

Material described by Schr.otter 44 as opaline allophane from the vicinity of Freienstein, Styria, in 

1837, was named" schrotterite" by Glocker 45 in 1839. 

These materials all agree in being amorphous and 

in containing essential silica and alumina with a large 

but variable proportion of water. Many specimens 

containing various proportions of bases have been reported, and plumballophane 46 has been identified 

from Monte ·· Vecchio, Sardinia. Allophane from . 

Styria has a blue color due to the presence of chrysocolla.41 · Small amounts of 803 have been reported in 

the material from Styria and from Sand Mountain, 

Cherokee County, Ala.48 Some of the allophane 

&tudied in the preparation of this report was found 

to contain a notable proportion of P 20 5. 

The descriptions of allophane and related min~rals 

given in the literature indicate the great variability of 

the materials. All are described as amorphous, but 

this term has been applied to very finely crystalline 

as well as truly amorphous material. An examination 

of samples labeled " allophane " in the collections of 

the United States National Museum shows that many 

of these are finely crystalline, being most .commonly 

impure halloysite. It seems evident that only truly 

amorphous material should be termed "allophane" and 

that all crystalline or submicroscopically crystalline 

materials should be assigned to some other mineral. 

The X-ray methods of study have made it possible to 

distinguish amorphous from submicroscopically crystalline materials, as was not possible when these materials were first studied. The character of most of 

the previously described materials cannot be determined, as only a few are available for restudy, and old 

descriptions and analyses are for the most part useless. 

However, the published analyses serve to indicate the 

variability of the material that has been described as 

allophane and schrotterite. In 12 analyses of allophane given in the literature the Si02 ranged from 

21.39 to 39.13 percent, the AlzOa from 23.52. to 41.66 

percent, and the HzO from 33.06 to 43.96 percent. 

44 Scbrotter, Anton, Uber den untheilbaren Opaline-Allophan, ein 

neue Mineral-Species: Zeitscbr. Phys. u. Math., vol. 4, pp. 145-150, 

1837. 

u; Glocter, E. F., Handbuch fiir Mineralogie, 2d ed., p. 536, 1839. 

. 46 Bombicci, Luigi, Plumballofane di Sardegna: Soc. ital. sci. nat. 

Atti, vol. 11, pp. 114-118, 1868. 

' 7 Schrotter, Anton, Jour. prakt. Chemie, vol. 11, p. 380, 1837. 

' 8 Mallett, J. W., On scbrotterite from Cherokee County, Ala.: Am. 

Jour. Sci., vol. 26, p. 79, 1858. 

That is, the silica-alumina ratio ranged from 0.74:1 

to 1.98: 1, about one-half being not far from 1: 1. 

The ratio reported in schrotterite ranged from 2.15: 1 

to 2.73: 1. · . 

CHEMICAL COMPOSITION 

Chemical analyses of five specimens of allophane 

from widely separated localities are given in the first 

table below, and analyses of related minerals in the 

next table. . 

·Chemical analyses of allophane 

1. Liege, 2. More- 3. Laurium, 4. Dutchess 5. Monte 

Belgium bead, Ky. Greece County, Vecchio, N.Y. Sardinia 

Si02---------- . 33. 96 27. 61 28. 60 25. 19 32. 30 AbOa ____ _____ 31. 12 32. 29 31. 66 36. 53 30. 41 

Fe20aa _______ .. Trace . 23 . 16 . 78 . 23 MgO ____ _____ -------- . 10 . 12 . 02 . 29 CaO _________ _ 2. 26 . 02 . 20 . 04 . 02 

K20+Na20 ___ -------- . 10 . 28 . 10 . 10 

H20- _______ _ 12. 84 19. 36 19.26 21. 20 16.38 

H20+ _; ______ _ 20. 28 18.05 14. 64 15. 76 14. 43 

Ti02--- ____ ___ -------- None None None None CuO _________ _ -------- -------- . 96 -------- 1. 60 ZnO _________ _ -------- -------- 2. 62 -------- 4. 06 C02 _________ _ -------- . 72 1. 20 1. 04 . 65 

P20s- ________ _ -------- 1. 31 None . 02 . 02 

SOa----- _; __ ___ -------- . 12 . 04 None . 21 

100. 46 99.91 99.74 100. 68 100. 70 

"The iron is all assumed to be present as Fe20a, as the ferrous iron in clay minerals is commonly within the limits of analytical error. 

Analysis ·1 by L. 'r. Richardson; 2-5 bY. J. J. Fahey. 

The materials whose analyses are given in the fore-

. going table are all essentially hydrous aluminum 

silicates with minor propo:rtions of various bases. 

The water is high in all of them, varying from 

30.81 to 38.00. The ratio of aluminum to silica is 

as follows: Liege, 100 : 176; Morehead, 100: 123; Laurium, 100: 152; Dutchess County, 100: 112; and Monte 

Vecchio, 100.: 180. All the samples of allophane contain bases, but they are negligible in the material from 

Morehead and are highest in the material from Monte 

Vecchio, where the ratio between total RO bases and 

silica is only about 1:7. The most abundant bases are 

copper and zinc in the specimens from Laurium and 

Monte Vecchio, where these minerals are associated 

with ore deposits. 

Some of the specimens of allophane and schrotterite 

were found to have chemical compositions which indicated that they were intermediate between normal 

allophane and evansite. The chemical analyses of 
146 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

phosphate-bearing allophane and related evansite are 

given in the following table: 

Ohemica.Z ooaZyses of phosphate minerals .· 

•. 11 2 

Si02------------------ -- ~ 21. 26 4. 34 Alz03- _____ _____ - _- _ _ _ _ 34. 95 41. 41 

Fe203--'------- ------------ · a. 10 a. 86 

FeO MgO ______ -------------- - ------------------- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . 05 . 22 

CaO _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ None . 20 

K20+Na20 _______ _______ - ----- ---- . 10 

H2o-___________________ 14. 85 20. 92 

H_20+-------- ----------- . 21. 3_8 14. 43. T1 02 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ None 

Cu 0 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1. 80 

ZnO _____ -------------~-- __________ 4. 30 

002------- ------------- ---------- 2. 07 

P20s----------·---------- 7.15 9. 23 

803- - ------------------- ---------- . 08 

99. 74 99. 96 

" '!'he iron is all ~sumed to b.e present as .Fe20a. 

34. 48 

5. 49 

None 

Trace 

4. 32 

36.96 

19. 14 

.. 100. 39 

Analyses 1 and 2 by J. J. Fahey; 3 by Waldemar T. Schaller (Evansite from two American localities: U.S. Geol. Survey Bull. 490, p. 94, 1911). 1. Al.}.ophane-evansite from Huron, Lawrence County, Ind., where it is associated with halloysite. 2. Allophane-evansite from Freienstein, Styria. 3. Evansite from Gold burg, Idaho. 

The analysis of a specimen of beautiful water-clear 

allophane associated with hailoysite ( indianaite) !rom 

Huron, Ind., shows 7.15 percent of P 20 5 • A. slightly 

blue "schvotterite" from Dollanger Mountain, Frei-· 

enstein, Styria (Roebling collection of the National 

Museum), contains only 4;g4 percent of silica but 9.23 

percent of P 20 5 • Another specimen from Brandberg, 

Styria, showed abundant P 20 5 by a qualitative chemical test. It has been previously recognized -that schrotterite was probably not a definite mineral, for Helmhacker 49 states that the schrotterite from the type. 

locality (Freienstein, Styria) is a mixture of an earthy 

and. a glassy clear n1aterial. The glassy material is 

halloysite and tlie earthy.material variscite. Brend--

ier 50 reports that both the materials fro'm Freienstein and Cherokee County, A.la., are mixtures of 

variscite and halloysite. "Schrotterite" from Saalfeld, Thuringia, has been analyzed by Zambonini 51 

but without testing for P20 5. 'This material has not 

been available for reexamination, but as P20 5 would 

not be recognized unless expressly looked for ;it may 

be present in the Thuringian material. 

4Al Helmhackei', R., Einige Mineralien aus der Gruppe der Thone : 

Min. pet. Mitt., Band 2, pp. 238-239, 1879. · 60 B,rendler, Wolfgang, Mineralien-Sammlungen, Teil 2, p. 215, 1912. 61 Zambonini, F., Melit, ein neues Aluminium-Eisen Hydrosilicat aus 

Thiiringen, non .. Schrotterit beglietet: Zeitscbr. Kryst. Min., vol. 32, 

p. 161, 1900; Uber Millerit, Melit und SchrOtterit: Idem, vol. 34, 

pp. 225-227, 1901. 

A. material to which the ·name viterbite has been 

applied, from. Santa Rosa de Viterbo, Boyaca, Colom1 bia, has the following chemical composition: 52 Si02; 

' 21.0; A.l20 3 , 40.0:; Fe20s, 3; P 205, :6.0; H20; 30.7. 

, The index or ·refraction determined on. type material 

I is n:== 1.476~ 'Thus ·.the· chemical and · optical proper:: 

ties are similar to those of the aJlopluine-eyansite from 

H~ron, Ind . .. A. study o£ ·the .foregoing·. analyses indicates that then~ may be all variations _between typi~. 

ral phosphate-free 'allophane and evansite. 

Optical studies, X-ray diffraction patterns, and de-

:. hydration curves __ all show th~t allophane and .related 

: materials have no · definite atomic _ structure but ar.e 

. amorphous-that is, they are structureless mutual so:; 

lutions of. various oxides. and· water. Such :materials 

can have .no definite chemical composition, and wide 

I variations.in composition are to be. e~pected. In dis-, 

; cussing chrysocolla Foote and. Bradley 53: !:lay: I ' 

.The mine~al~ which appear to pres~nt the gre~test difficulty 

in the relations between actual coniposition and formula ·. are ; 

those which commonly ~ccur in the amorp~OU!? condition, but· 

in these cases, as with well-crystallized minerals, definite 

formulae are commonly given in all reference . works on the 

subject. . An, examination of the facts will show, however, th:;..t 

· in many amorphous minerals the actual composition found 

may differ very widely indeed from ' the theoretical value re-' 

quired by th¢ formula: * . ··* · * The mineral [chr;ysocolla] ' 

is not a chemical compound, and no ~ formula should be as-· 

· signed, out a solid solution of copp.er oxide, silica, and water 

as essential compon~nts, whose composition depends upon the ~ 

conditions of formation. * * * This tentative view of the· 

composition of chrysocolla, if generally adopted, should logh · 

cally be extended to a larg~ numper of m_inera,ls which:. com-

. monly. occur in the amorphous condition. 

, As allophane is essentially an amorphous solid solu-. 

tion of silica, alumina, and water, and evansite is ·an.' 

amorphous solid solution of phosphorus, alumina, and. 

water, it is to be expected that the· two types :of mate-: 

rial may occur together as. a homogeneous mixture. 

It is also evident that other amorphous :materials may ~ 

enter into such a solution. Thus the .allophanes fr.om 

Greece and ~tyria .. contain copper, which. no doubt . 

represents. chrysocolla that is in :solution in the allophane. 

The analyses -reported in . this . paper and earlier 

I studies by others have discredited ~ll the known re-

. ported occurrences of schrotterite, including the type , 

n1ateriaf, except only that from Thuringia, and even 

this may .. be ph_osphate-bearing. Even if an am or-

: phous hydrous aluminum. silicate with a higher pro62 Codazzi, R. L., Notas mineralogicas y petrograficas, p. 26, Bogota. 

Biblioteca del Museo nacional, 1925. · 53 Foote, H. W., and Bradley, W. M., On the solid solution in minerals; IV, The compo-sition of amorphous minerals as illustrated by 

cbrysocolla: Am. Jour. Sci., 4th s:er., vol. 33, pp. 180--184, 191

13. 
HALLOYSITE AND ALLOPHANE 147 

portion of aluminum than normal allophane does exist, 

it. is best grouped with allophane. It is therefore 

evident that schrotterite should be entirely discarded 

as a mineral name. , 

Materials of this type introduce a problem in mineral nomenclature. Crystalline minerals ha'1'e definite 

compositions, or vary only within definite limits, and 

so differ fundamentally from the amorphous materials. For this reason such amorphous materials have 

been called " miner a] oids " to distinguish them from 

true minerals, although they are commonly listed· · 

as minerals in nearly all mineralogies and no doubt 

·will continue to be so classified. However, the assignment of distinct names to members of a group of 

amorphous materials differing only in the proportions 

of their essential constituents, as has been attempted 

for allophane and schrotterite, is not justified, but a 

single name should be applied to an entire group. On 

the other hand, it is · evident that a different name 

. should be applied where· the essential constituents are 

ctifferent . . Thus we .would have allophane, evansite, 1 

and chrysocolla as distinct minerals or mineraloids. 

From their nature these· minerals may show mixtures 

with on1

e another, and when these mixtures 'reach 

noticeable proportions they :rp.ay best be described by 

using the two names connected by a hyphen. Thus 

the mixtures ·considered · in this paper may best be 

described as allophane-evansite and allophane-chrysocolla. It is to be distinctly understood, however, that 

these rare not to be considered mineral species but 

nlei'elr mixtures of minerals. 

· OPTICAL PROPERTIES . 

The optical properties of a representative group of 

allopHanes are given in the following table: 

Optical properties of allophane and related phosphatic materials 

Locality Name 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Liege, Belgium ____ ·_________________________ Allophane _______ _ 

Clove ~~~~~~a~ere~;~~~==========~============= mine, Dutchess County, N.Y ________________ =====g~=========== do _____ __ ___ _ Monte Vecchio, Sardinia _________________________ do __________ _ Bedford, Ind ___ _ :. __ ,.. ___ -.- _______________________ d<?- _________ _ 

Huron, Lawrence County, Indiana ___ __ ____________ do __________ _ 

Dollanger Mountain, Freienstein, Styria___ _ _ _ _ Schrotterite _____ _ _ Brandberg, Styria _______________________________ do __________ _ 

10. 

11. 

Viterbo, Colombia __ __ ______________ __ ------ Viterbite_-- -.---- _

1 

Gold burg, Idaho____________________________ Evansite _________ _ 

a Slightly variable. 

No. 11 determined by F. E. Wright (Schaller, W. T., op. cit., p. 95); others by C. S. Ross. 

This table shows that there is only a small variation 

in the indices of refraction, even where there IS a 

large difference In the chemical composition; the 

greatest variation IS from n= 1.468 to n= 1.512, and 

most of the specimens are not far from 1.485. It IS 

therefore evident that these minerals carinot be ·distinguished either by the optical or the X-ray properties, and chemical analyses are necessary. X-ray diffraction patterns are characterized by absence of all 

but traces of lines. One diffused band and traces of 

others are all that appear. Such traces as can be 

vbserved, however, are the same in different patterns. 

DEHYDRATION 

Two typical allophanes have been subjected to dehydration tests, and the results are given in the following 

table and the curves in figure 8. 

' 

Color 

Index of refraction /-----------;-------

I 

1. 472 

1. 485 

1. 485 a 1. 480 

1. 496 

1. 468 

1. 475-1. 485 

1. 512 

1. 475 

1. 476 

1. 485 

Hand specimens 

Colorless ______ :... ___ _ 

Pale brown ________ _ Sky blue ___________ _ 

Sulphur yellow _____ _ Light blue _________ _ Color less __________ _ _ ::: ____ do __________ · __ _ 

Pale blue __________ _ _____ do ____________ _ 

White _____________ _ 

White to brown ____ _ 

Thin sections 

Colorless. 

Do. 

Do. 

Do. 

Very light blue. 

Colorless. 

Do. 

Do. 

Do. 

Do. 

Nearly colorless; 

Dehydration data of allophane 

Liege,· Belgium Morehead, Ky. 

Temperature Loss of water Temperature Loss of water 

(° C.) Percent (° C.) Percent 

26 0 26 0 

120 15.00 40 4. g9 

1()0 18. 60 100 12. 98 

185 19. 67 160 15. 88 

201 20. 18 240 18. 47 

225 20. 67 300 19. 78 

250 21. 79 410 22. 06 

285 23. 52 562 25. 58 

330 25. 04 615 25. 71 

360 25. 95 795 27. 34 

450 28. 93 

502 29.71 

570 30. 38 

6:30 30. 92 

710 31. 27 

850 31. 67 

' 
148 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 3 4-3 5 

The dehydration data given in the preceding table 

and the dehydration curves plotted therefrom show a 

gradually decreasing loss of water, with no break or 

35 

30 

1-25 

z 

w 

0 

0:: 

w 

Q 

z20 

0:: 

w 

~ 

~ _15 

LL 

0 

(/) 

(/) 

0 

_j 10 

5 

. 

/ 

v 

/ ~ 

t: v 

J 

v 

f 

f 

in the high-temperature water of combination in 

the kaolin minerals kaolinite, dickite, nacrite, and 

halloysite. 

- l.--e---"Li 

"<7 

~ ~ge, Belgium 

v- -b 

~ 1.---

___.o-- ld, Kentucky 

v v 

300° 400° 500° 

TEMPERATURE 

FIGURE B.-Dehydration curves of allophane. 

prominent flexures. This shows that in allophane 

there is no difference in the manner in which the water 

is combined at high and low temperatures. The curves 

are characteristic of a material in which the water is 

held in solution and not in chemical combination, as 

0 

This confirms the chemical and X-ray data, which 

show that allophane has no definite atomic structure 

or chemical composition and is a mutual solution of 

silica, alumina, _water, and minor bases and accessory 

acid radicles~