Halloysite and Allophane Page: 135
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HALLOYSITE AND ALLOPHANE
By CLARENCE S. Ross and PAUL F. KRmBABSTRACT
This paper is a continuation of the study of the kaolin min-
erals, in the first part of which, published in 1931, 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 mineral
of the kaolin group, closely related to but distinct from
kaolinite. The chemical, optical, X-ray, and dehydration
properties of a representative group of halloysites are recorded,
all these being new data determined by the authors on sepa-
rate portions of single samples whose purity has been care-
fully tested.
Halloysite has been previously described as amorphous, be-
cause the microscope commonly reveals no evidence of crystal
structure. X-ray diffraction studies, however, show that it
has a crystal structure, being made up of crystal grains 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 commonly the
result of hydrothermal processes.
Allophane is an amorphoussmaterial 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 of normal allophane and evansite, an amorph-
ous 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 years.
In an earlier paper the minerals kaolinite, dickite,
and nacrite were described. These studies have been
continued, and the present paper sets forth the results.
Halloysite, like those earlier described, is a mineral of
the kaolin group. 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.HALLOYSITE
A white or light-colored, approximately isotropic
clay mineral known as "halloysite" locally forms
small nearly pure masses or is abundantly associated
with kaolinite in many kaolin deposits. The associa-
tion, 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
a distinct mineral. Not all nearly isotropic clay ma-
terials are halloysite, for some prove to be very fine
grained kaolinite, and others are clay material of a
quite unrelated group. On the other hand, most iso-
tropic clay materials with an index of refraction near
that of quartz are the definite clay mineral halloysite.
The original halloysite was found in the Carbonif-
erous limestone of Angleur, Liege, Belgium, in a dis-
trict of old 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 ma-
terial 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 been 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 com-
pared with halloysite from other localities. Halloysite
has also been compared with the related kaolin min-
erals-kaolinite, anauxite, nacrite, and dickite-and
VQ ith other clay minerals. The method of study em-
ployed in this work is described in the paper on the
kaolin group, already cited. All determinations-
optical properties, X-ray diffraction data, and chem-
ical analyses-have been made on different fractions
of the same sample. The chemical and optical studies
have been carried on in the laboratories of the United
2 Berthier, P., Analyse de l'halloysite : Annales chimie et phys., vol.
32, pp. 332-335, 1826.
135
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Ross, Clarence S. & Kerr, Paul F. Halloysite and Allophane, report, 1934; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc957813/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.