AmericanMineralogist,Volume61, pages 3/,1-317,1976
Alunogen,Alr(HrO)r2(SOn)s.5HrO:Its atomic arrangementand watel content
JBNHo FeNc e.NoPnul D. RoslNsoN
Departmentof Geology,Southernlllinois Uniuersityat Carbondale
Carbondale.Illinois 62901
Abstract
Alunogenis triclinic,spacegroup PT with a = 7.a20$)A; b : 26-97(2)A;c : 6.062(5)A;a
: 89'57(5)0
l eude r g e r - S u p p e r
' ; : 9 7 " 3 4 ( 5 \ ' ;f : 9 1 ' 5 3 ( 5 ) ' ; a n d Z : 2 . A c o m p u t e r - c o n t r o lB
geometry)was utilized for collectionof X-ray intensity
two-circlegoniometer(Weissenberg
data.The structurewas partially solvedby the symbolicadditionmethodand completedby
refinement,with
Full-matrix least-squares
use of Fourier and differenceFourier syntheses.
0.077.
index
of
led
to
a
final
R
1675reflections,
by a networkof
The structureis built of discreteSOnand Al(Ow). polyhedrainterconnected
hydrogenbonds.Four of the five independentpolyhedraare spatiallyarrangedin a manner
sheetsparallel to (010),therebyaccountingfor the (010)
which givesrise to pseudo-double
and twinning.The fifth polyhedron(an SOrgroup) is situatedbetweenpseudo-sheets
cleavage
and is completelysurroundedby the five zeolitic water molecules.Mean AI-Ow and S-O
distances
are 1.887and 1.467A, respectively.
Maximum HzO contentin the alunogenformula was found to be 17moleculesas opposed
to the heretoforeacceptedvalue of 18. Partial dehydration is accompaniedby partial
of zeoliticwatersites.That thereexistsno known aluminumsullatehydrateother
occupancies
than alunogenis interpretedto be a result of the strongtendencyfor the Al3+ ion to form
A(HrO)3+in aqueoussolutions.
Data collectionand reduction
Small,transparentlathsof alunogenfrom KbnigsRecentinterestin crystallinehydrateshas, as one
general
Schemnitzdistrict,Hungary(now Nova Bana,
berg,
the
of
the
revelation
of its major objectives,
were kindly suppliedby Professor
via
Czechoslovakia)
crystal-strucattempt
an
rulesof solvation,i.e.,
Laboratoirede Mineralogieet de
the
of
F.
Cesbron
the
unravelling
toward
made
ture analysisis being
la Sorbonne,Paris,France'The
de
Cristallographie
in
crystalpolyhedral
clustering
relationshipbetween
line hydratesand the polyhedrawhich existedin the crystalsare stablewhile in the samplevial. However,
solution from which the mineralsgrew. Despite a if the crystalsare exposedto the atmosphereduring
considerableamount of existingdata, there is little periodsof low humidity,dehydrationbeginsalmost
of the behaviorof polyhedrain immediately,beginningas small cracksvisibleonly
real understanding
to tingesof
solutionor the multiplicityof their phaseformation. underthe opticalmicroscope,progressing
In thispaper,we reportthecrystalstructureofaluno- white on the grain edges,and terminatingwith the
gen,a sulfatehydratewith a very high water content. entire grain becomingwhite, translucent,and crumBy virtue of its large number of water molecules, bly. This occurswithin a few hours during unusually
alunogencan be thought ofas beingcloselyrelatedto cold winter dayswhen indoor humidity is very low'
solutions.Thus, its crystalstructureis of greatinter- However,crystalsexposedto the atmospherefor peestsinceit may providea key to thesequestions.This riods of severalweeks during the humid summer
studywill alsosettlethe questionof the exactnumber monthsshowedno deterioration.ln additionto the
of water moleculesin the alunogenformula and dehydration problem, alunogen is commonly
time was
should also yield considerableinformation con- twinnedparallelto (010),so considerable
crystal.
a
suitable
finding
cerningthe hydration range in which the alunogen spentin
The unit cell parameters,obtainedfrom precession
structurecan exist.In this paper we extendthe conphotographs,
area : 7'4206)A;b : 26.97(2)A; :
clusionsreachedby us in connectionwith the struc"
6.062(5)A;a : 89"57(5)';0 : 97"34(5)';1
ture of kornelite(Robinsonand Fang, 1973).
Introduction
3 ll
3t2
J. H. FANG AND P. D. ROBINSON
9 l ' 5 3 ( 5 ) ' ; Z : 2 a n d s p a c eg r o u p P l o r P I . T h i s u n i t
cell was chosen so as to conform to the morphological cell of Gordon (Palache, Berman, and
Frondel, l95l).
The crystal selectedfor data collection was a thin,
transparentlath with the dimensions0.016 X 0.010 X
0.0026 cm. The shortest dimension very nearly parallels the b axis about which the crystal was rotated
during the intensity gathering process.A total of 2822
raw intensities were collected with a computer-controlled, Buerger-Supperequi-inclination goniometer
and Ni-filtered CuKa radiation. Scan speed was varied directly with peak intensity in order to minimize
variations in counting statistics.Pre-selectedstandard reflections were manually remeasured between
reciprocal lattice levels as a check on system and
crystal stability. The system performed normally during the course of the data collection and the crystal
remained stable.
All data were corrected for Lp and absorption (p :
46.06 cm-r) using the Acec program of prewitt
(Wuensch and Prewitt, 1965).
Structure determination
Normalized structure factors (E s) were calculated
using the Wrlxonu program of Fang and Robinson
(1969). The strong indication of centrosymmetryindicated by the E statistics led to adoption of the space
group PT.
A modified version of the reiterativeSayre'sequation program written by Long (1965) failed to reveal
the structure. We then proceeded to perform semimanual sign prediction with the aid of a symbolic
addition program known as SyMBAD,written by Robinson (1974) for our Pop-8/e computer. ln this manner we were able to deducethe signs or symbols of
125 hkl's. This information was then given to the
Sonrs symbolic addition program of Bednowitz
(1970), for extension to hkl's with lower E values.
After signsor symbols for 530 hkl'swere determined,
.E maps were calculated on the three possible sign
combinationsthat resulted.One set revealedall of the
polyhedral atomic sites as well as tentative zeolitic
water positions.
All polyhedral atoms were then input to the RrrNs
least-squaresprogram of Finger (1969) for calculation of structure factors, and the results were
passedto a Fourier program known as Fonoy (Ohya,
1970)for calculationof an Fo6"Fourier map. The Fo6"
map clearly revealed four zeolitic water (Zw) positions. However, the resultswere inconclusiveregarding the remaining two possible zeolitic sites which
would be presentif our sampleof alunogencontained
the full complementof l8 water moleculespreviously
attributed by Palacheet al (1951) and by Larsen and
Steiger(1928) to the fully hydrated mineral.
Completion and refinement of the structure
The R index became 0.083 after four cycles of fullmatrix least-squaresrefinement, using atomic scattering factors for Al3+, So,and O1-, from Cromer and
Mann (1968) and the 168l reflections which were
considered "observed" after passing the lI-B>
.v/T+tsI test (where 1 : total counts accumulated
during the scan and B : total background). During
the final cycle, A values (4-4) were passedto the
Fonny program previously mentioned for
calculation of a differenceFourier map. The largest
peak appearedat a very logical location; however, the
low electron density of the peak could only be explained by assuming partial occupancy. Two leastsquarescalculationswere performed in an attempt to
fix the occupancyvalue of this site,herein designated
Zw(5). First, a five-cyclerun was prepared in which
the occupancy factor was given a fixed value for each
cycle, beginning with l0 percent occupancy and
changing by l0 percent increments for each additional cycle until a 50 percent occupancy value was
reached. During each cycle the occupancy value of
Zw(5) was locked, but all xy,z's and B's were allowed to vary. During the l0%o-occupancycycle the
temperature factor became -17.04'. As the occupancy was increased, the R factor decreasedand the
temperature factor increased until, at 50 percent occupancy, the R factor again began to increaseand the
temperaturefactor becameunreasonablyhigh. At 30
percent occupancythe B for Zw(5) was t6.1A' while
at 40 percent occupancy ^Bwas 9.lA'. The R index
was at its minimum of 0.078 during the 30 and 40
percent occupancy cycles. Thus, it seemed
reasonable,in light of the temperaturefactors of the
other zeolitic waters, that the occupancy for Zw(5)
was between30 and 40 percent.Second,attackingthe
problem from the opposite direction, the temperature
factor of Zw(5) was locked at the averageB value of
the other four zeolitic water molecules(6.2 A,; and
the occupancyvalue of Zw(5) was varied, along with
all atomic coordinates and .B's of the other atoms.
The occupancyvalue of Zw(5) refinedto a value of 37
percent. It is possiblethat the Zw(5) occupancymay
be sfightly higher since the B of Zw(5) could well bd
somewhat higher than the average of the full occupancy zeolitic waters. However, we believe our reported value is very close to the true occupancy.
ALUNOGEN: ATOMIC ARRANGEMENT AND WATER CONTENT
We next began a search for evidence of a sixth
zeolitic site. We added the partial occupancy Zw(5)
position to the list of atoms, refined the structure to
an R index of 0.077,and then calculateda difference
Fourier map. The map showed no feasible atomic
positions and thus it was concluded that the sixth
zeolitic site was non-existent,at least in the crystal
under study.
At this point, six ftkl's, obviously affectedby extinction, were removed from the data and two additional least-squarescycles,with 1675 reflections,led
to the final R index of 0.077. Observedand calculated
structure factors are given in Table l1 while atomic
'To obtain a copy of Table 1,order Document AM-75-005 from
the Business Office, Mineralogical Society o[ America, 1909 K
Street, N.W , Washington, D.C. 20006. Pleaseremit in advance
$1.00for the microfiche.
Ttsre 2. Atomic Coord'lij:XXl
Factorsfor
Temperature
313
coordinatesand temperaturefactors are presentedin
Table 2.
Description of the structure
The structure is composedof isolatedAl(Ow)' octahedra and SOr tetrahedra (Fig. 1). However, the
polyhedra are not evenly distributed throughout the
unit cell as they are, for example, in the alum structure (Cromer, Kay, and Larson, 1967); rather, they
form pseudo-doublesheetsparallel to (010). Between
the pseudo-sheetslie the S(3) tetrahedra which are
completely surrounded by zeolitic water molecules.
In addition, it is interestingto note that the octahedra
and tetrahedralie in separatebut parallel sheetsnormal to (001). This is best visualized in the (100)
projection (Fig. l).
All polyhedra are quite regular (Table 3), as would
be expectedin an isolated polyhedral arrangement.
The mean Al-Ow and S-O distancesare 1.887 and
1.467A, respectively.
Discussion
B(fr2)
Atom
s ( r)
s(2)
s( 3 )
A r( 1)
A l( 2 )
.2327(4)
.2424(4)
. 6 3 3(45 )
.2803(5)
.7367(5)
. 9 3 e 0l(
.5607(t
.7470(l
.0985( l
. 5 9 9 5( r
. 4 8 r3( 6)
. 4859(5)
. 4 74 o ( .)7
0(l
0(2
0(3
0(4
.374(r)
.6e7('r)
. e 2 8 )( r
.e043(3)
. 0 2 5 83( )
.0886( 3)
.e656(3)
.448(2
.340(2
. 4 5 7( 2
. 2 7 1( 2
t.5\z )
, al2\
o(s)
0(6)
o(7)
o(8)
. 6 e 3 )( r
.3er('r)
. e o 8 )( r
.r74(r)
.4738(3)
. 3 3 6( 2 )
(2)
.447
. 4 4 6 ()r
2.3(2)
2.1(2)
2.0(2)
. L r r \ ! t
L . L \ L /
0(e)
o(10)
o(r'r)
o(12)
.232(2)
. 6 0 4r()
. 7 0 3 ()r
( 2)
.543
.28r4(4)
.7268(4)
. 7 e 8(r4 )
.2s28(s)
.387(2)
.24s(2)
.466(2\
.437(2)
4.8(3)
3 . 7( 2 )
4.2(2)
6.6(3)
0w(l)
0w(2)
0w(3)
0w(4)
0 w ( 5)
0w(6)
.Br2(r)
.334(1)
.374(r)
. 7 7 (r r )
. 4 8 2r()
. 0 4 6 ()r
.84r5(3)
.r254(3)
.037e(3)
.e304(3)
(3)
.882e
.0774(3)
.1r3(2)
.28e(r)
.il2(r)
. 2 8 5 () r
. o s 3 () 1
. 0 6 2 () r
2.3(2)
r.e(2)
r.8(2)
r.6(2)
r.e(2)
2.0(2)
0w(7)
0w(8)
0w(9)
0 w( 1 0)
0 w ( lI )
0 w ( l2 )
. 8 2 8 ()r
. 3 0 3 ()r
. 0 2 (7t )
. 7 7 (71 )
. 4 e 7 ()r
.36r(r)
. 6 6 0(33)
.3725(3)
. 4 r7 e( 3 )
.56e6(3)
. 6 r4 s( 3 )
.4622(3)
. r 2 8 ()r
2.0(2)
1 . 7( 2 )
2.0(2)
i.5(2)
1. 7( 2 )
zw(l)
zw(2)
zw(J/
7w(4).
Zw(5 )D
. 7 0 e ()l
.6il(2)
.oo2(2)
.1s2(2)
.r48(s)
.324s(4)
. 2 r o (r 5 )
.2164(5)
.6e6s(5)
(11
.7s7
.201(2)
.043(2)
. r 0 r( 2 )
.?2e(3)
.434(6)
t7Ell\
Eo6E/?\
.4r 4(3)
.5336(3)
r.45(6)
1.23(6)
2.54(8)
1.27(7)
.oor2(7)
(6)
.002e
i.re(7)
t-rolr\
.282(1)
. 0 4 7 ()r
.287(r)
4.6\L
)
2.5(2)
t
t(r\
.os2(r) 'r.5(2)
.r2r(r)
4.4(3)
s.e(3)
7 . r( 4 )
7 . 6( 4)
6.2c
Hydrogen bonds
A hydrogen bonding scheme, derived from geometrical considerations,is shown in Table 4 (the arrows point toward the acceptor atoms of the Hbonds). It is interestingto note that the only zeolitic
water not bonded to a ligand water is Zw(5), the site
of partial occupancy.Thus, alunogen owes its existence as a crystalline solid to the extensivethree-dimensional network of hydrogen bonds. Table 5 is a
summation of donor and acceptor bonds, in support
of the proposed hydrogen-bondingscheme.The electrostatic bond strengths and their sums about the
anions are shown in Table 6. Anions which have
nearly identical environmentshave been grouped together. We note from the table that, with one exception, the oxygen atoms are undersaturated,and that
this imbalanceis reflectedin the shorter-than-normal
Ow-O distancesshown in Table 4.
Chemical formula of alunogen:
Reuision of the water content
In the Refinementsection,we pointed out that we
were unable to locate a sixth zeolitic water from the
final difference Fourier map, despite the fact that a
sixth site should exist if alunogencontains a total of
l8 HrO moleculesas reported in the literature. This
information was in contradiction with our working
hypothesis concerning zeolitic water sites which
states that the loss of water in sulfate hydrates does
J. H. FANG AND P. D, ROBINSON
F''.-"-F"t.Fl
I
Owl0
otl
.*u
zw2
F I c . l . P o l y h e d r a l r e p r e s e n t a t i o no f t h e a l u n o g e n s t r u c t u r e .
not causethe disappearanceof an entire zeolitic water site, but rather is the result of a decreasein occupancy of one or more sites.In an attempt to discover
the source of the difficulty, we recalculated the chemical analysesreported by Dana (Palacheet al., 1951,
p. 537). None of the four chemical analyseslisted
corresponded to 18 HrO-they vary from 12.5 to
15.5-and the origin of the l8 HrO hydration state
was attributed to the work of Larsen and Steiger
(1928). Howevsl, what Larsen and Steigerstatedwas
that ". . . former contention as to whether alunogen
contained I 6 or I 8 molecules of water has been raised
on the incorrect assumptionthat the water is present
in a definite, fixed molecular proportion."
Furthermore, they concluded that their study "indicatesa water content of from l5 to 15.5molecules."
Rather it was Lausen(1928)who actually inferred the
water content to be 18,basedon his chemicalanalysis
of impurity-containing alunogen from Jerome, Arizona. His calculationsshowed the molecular ratio of
A l r O ' : S O ' : H r O t o b e 1 . 0 : 3 . 5 : 1 8 . 6H. o w e v e r , i t i s o b vious the ratio must be normalized to 0.9:3.0:15.9,
thus indicating a water content of 16. In short, the
number 18 was not supported by any published account. Notwithstanding, a survey of the literature on
synthetic alunogen proved very enlightening.In his
effort to clear up the confusion in the chemical literature regarding aluminum sulfate, Smith (1942) repeated chemical investigations of parts of the system
AlrO3-SOs-HzO.His summary states"Previous data
in the literature have been reviewed and shown to
lend little support to the reported formula of
Alr(SO4)s.l8HrO for hydrated aluminum sulfate."
He further wrote that the compound is either a hexadeca-hydrate or heptadeca-hydrate, the latter favored by him as well as by two other investigators. In
a later paper, Henry and King (1949) reported that
alunogen is a l6-hydrate. Thus it seemsalunogen is
either a l6- or l7-hydrate; but which is correct?
As is often the case, the exact chemical composition can only be established via three-dimensional structural analysis.We have demonstratedthis
in our previous papers, and again emphasizethis fact
by showing that alunogen is a heptadeca-hydrate
when fully hydrated. Further loss of water can be
expected to induce further partial occupancies in
other zeolitic sites, in order to sustain the alunogen
structure.
Crystallization in the Fer(SOn)s.nH"O and
Al2( SOn)r.nHrO systems: An interpretation
One salientobjectivein crystal-structureanalysisis
to find or attempt to find a relationship between the
crystal structureand the ionic speciesexistingin solutions from which crystallinesolids grew. Toward this
end, a hydrate of high water content is a good candidate, since it can be thought of as being very similar
ALUNOGEN: ATOMIC ARRANGEMENT AND WATER CONTENT
Tenlr 3. SelectedInteratomicDistancesand Anglesfor Alunogen*
T e t r a h e d r a l c o o r d i n a t i o n a r o u n dS
0 ( t) - 0( 2)
MEAN
'I
.4734
s ( 2 ) - o ( 5 )r . 4 5 s ( e ) A
s ( 2 ) - 0 ( 6 )1 . 4 6 7 ( e )
s ( 2 ) -(o7 ) 1 . 4r7( e )
s ( 2 ) - 0 ( 8 )r . 4 7 4 ( e )
I .46efr
s( 3) - 0 ( s) I . 4 6 ( t) [
s ( 3 ) - or o( ) 1' r. 4 6 ( )r
s ( 3 ) - or()r . 4 6 ( r )
s ( 3 ) - o ( r 2r). 4 8 ()r
I .464
0 ( l) - 0 ( 4 )
0 ( 2) - 0 ( 3 )
0 ( 2) - 0( 4 )
0 ( 3) - 0( 4 )
2 . 3 e ()li
2 . 4 0 ()t
2.41(r)
2.41(1)
2 . 4 3 ()r
2 . 3 e ()t
0 ( 1) - s ( l) - 0 ( 2 )
o ( r) - s ( r) - o ( 3 )
0(r)-s(r)-0(4)
0(2)-s(r)-o(3)
0 ( 2 ) - s ()l- 0 ( 4 )
0 ( 3 ) - s ()r- 0 ( 4 )
10e.3(5)"
10e.5(s)
10e.7(6)
roe.6(5)
Il0.e(5)
r07.8(5)
MEAN
2.404
MEAN
I 0 9 .5 "
0(5)-o(6)
o(5)-o(7)
o(s)-o(8)
0(6)-0(7)
o ( 6) - o ( 8 )
o( 7) - 0 ( 8 )
2.3e(r)[
2.3s(1)
2.42(1\
2.40(r)
2.4r(1)
2 .3 q l)
o(5)-s(2)-o(6)
o(s)-s(2)-0(7)
0(s)-s(2)-o(8)
o(6)-s(2)-o(7)
o(6)-s(2)-o(8)
0(7)-s(2)-0(8)
r' r00e9..50( s ) "
( 5)
'r
10.9(5)
( 5)
ro e . 2
110.2(s)
l08.o(s)
MEAN
2.401
MEAN
0 ( r) - 0 (3)
s (r ) - o ( )i r . 4 6 2 ( t o ) A
s (1) - o( 2 ) 1 . 4 7 2 ( s )
s ( 1 ) - o ( 3 )r . 4 7 4 ( e )
s ( r) - 0 ( 4 ) r . 4 8 4 ( 1 0 )
1 0 9s. "
' | r or.( 7 ) '
o(e)-o(ro) 2.3sQ)R
o ( e ) - 0 )( r ' r 2 . 3 6 ( 2 )
o(e)-o(r2)
2.43(2)
o ( 1 0 ) - o ()i l 2 . 3 7 ( 2 )
0 ( r o ) - o ( r 2 )2 . 3 s ( 2 )
0(il)-0(r2) 2.38(2)
0(e)-s(3)-o(lo) 'r08.
2( 7)
0(e)-s(3)-o(rr)
0(e)-s(3)-o(r2) 112.2(81
o(ro)-s(3)-o(lt) 1
' r 0o 8
e .. 8 ( 6 )
o ( l o ) - s ( 3 ) - o ( 1 2 )' r 0 8o.(47)
(7)
o(ll)-s(3)-o(12)
MEAN
MEAN
23gA
I 09.5"
0ctahedral c o o r d i n a t i o n a r o u n dA l 3 +
o w ( )r - o w ( 2 )
0 w ( )1- 0 w ( a )
0 w ( )r - 0 w ( 5 )
'I
MEAN
.8904
o w l( ) - A l( l ) - 0 w ( 2 ) e 1 . e ( 4 ) "
0 w ( )l - A l( 1) - 0 w ( 4 ) 8 e . 9 ( 4 )
0 w ( )l - A l( l ) - 0 w ( 5 ) s 2 . l( a )
90.0
2 . 6 7A
.885A
'I
2 . 7 0 ()ri
2 . 6 6 ( )1
2.71(1)
I'IEAN
to a solution. Now that we have elucidatedthe struchavewe shedany light in
ture of a heptadeca-hydrate,
this regard? The answer is a qualified yes. The nucleation of alunogen crystalliteswas probably initiated
when the solution becameoversaturatedwith respect
to the composition-AL(So.)s(HrO)'r. l.5H,O-because l.sHro is the minimum amount of zeolitic
water required to build up the alunogen structure (if
2,674
MEAN
90' o
0.3 occupancy in each zeolitic site is taken to be the
minimum). As crystallizationprogressed,the up-take
of zeolitic water was increased,varying from the initial l.5HzO to 5HzO, when all zeolitic-watersiteswere
filled. The most outstanding feature of the
Alz(SOo)r.nH2O system, when compared with the
system,is the fact that a
analogous Fez(SOr)s.r?H2O
multiplicity of phases occurs in the latter (at least
316
J. H. FANG AND P, D. ROBINSON
Tnsrr 4.
Donor
P r o b a b l eH y d r o g e n B o n d s i n A l u n o g e n
Acceptor
Distance(A)
Angle(ADA)
0 ( 1 1)
Zw(3
)
?.644
2.57
4
I 12 . 3 "
+
+
0 ( r)
o(1r)
2.660
2 .5 8 6
93.3
+
0(2)
0(4)
2.637
2.662
1 0 2. 0
ow(a);
0(2)
0(3)
2.679
2.621
120.4
ow(s)]
0 ( i)
zw(2)
2.689
2.625
.|08.
2
ow(6)l
0(3)
0( 4 )
2.637
2.666
119.2
0(10)
zw(4)
2.651
2.562
1 0 7. 0
0w(8)
I 3[3]
2.732
2.592
118.2
ow(e)
I 3tl]
0w(r0)
I 3t;l
ow(r)
I 9i?lr
2.688
2.679
'106.7
2.665
2.694
'l't5.0
2.663
2.630
104.7
ow0z)
I 3i3]
zwo)
r 9iiii
2.639
2.665
104.7
2.771
2.987
122.5
zw(2)
I 3fi!]
zw(3)
r 9i?)r
2. 8 3 1
2.765
97.3
2.832
2.880
1 2 7. 3
zw(4)
r tiltl]
2.987
2.983
't2s.
1
*
r.w(5, *
2.719
2. 9 8 3
'113..|
,
0w(l) *
ow(2)
ow(3
)
,
ow(7
) *
0(12)
Zw(4)
Tesle 5.
Summation of H Bonds in Alunoeen
o
five), and yet there is only one aluminum sulfate
hydrate. This is especially puzzling when a limited
Al*Fe substitutionis found in coquimbite (Fang and
Robinson, 1970).An apparent answer would be the
non-availability of Fe3+during the mineralization of
alunogen, but then, why have no lower hydrates of
aluminum sulfate been found? We propose that the
reason may be found in the different ionic sizesof the
two otherwise similar ions. The aluminum ion is
nearly 30 percent smaller than the ferric ion, yet it
DAS
DAS
o w ( i)
0w(2)
0w(3)
ow(a)
0w(s)
0 w ( 6)
2
2
2
2
2
2
-2
-2
0w(7)
0w(8)
0w(9)
0w(10)
0w(11)
0 w (1 2 )
2
2
2
2
2
2
-Z
Zw(])
zw(z)
zw(3)
Zw(4)
2
2
2
2
2
2
2
2
4
4
4
4
zw(5/
.
|
5
34
-a
-2
0 ( t)
0(2)
o( 3 )
0(4)
22
22
22
22
0(5
0(6
0(7
0(8
22
22
22
22
o( e )
0(r0)
22
22
22
33
-L
-2
-z
-4.
-2
-4.
-2
o(il )
o(r2)
-2525
34 943
34 34 68
943
carries the same charge. The smaller the ion, the
stronger its polarization power and, in the presence
of a polar aqueoussolution, the aluminum ion has a
much stronger tendency than the ferric ion to be
enveloped by water, forming [Al(HrO)6]3+ groups.
This phenomena precludesthe possibility of aluminum bonding directly with sulfate oxygens,and the
resultant crystalline solid is a completely isolated
polyhedra of SO{ and Al(HrO)u, linked only by H
bonds to yield coherence.This may serveto explain
the fact that the highest n in the Alr(SOn).nHrO
systemis 17,whereasin the FedSOo)r.nH2Osystemit
is only I I (Thomas, Robinson, and Fang, 1974),with
no insular polyhedra.
From these observations and inferences we feel
that further structural studies of other crystalline hydrates are of significance if we are to bring progress
and new vista to the study of minerals.
TlsI-s 6.
Anion/Cation
Electrostatic Bond Strengths and Their Sums
about the Anions in Alunosen*
Al
H(a)
H(d)
po
0(1 to ll)
1.5
2 x l/6
I.83 v.u.
0(r2)
1.5
3 x 1/6
2.00
0w(l to 12)
2 x 5/6
2.17
Z w ( ]t o 4 )
2x1/6
2x5/6
2.00
zw(5)
lxl/6
2x5/6
1.83
ALUNOGEN, ATOMIC ARRANGEMENT AND WATER CONTENT
3t7
L A R s E N ,E . S . , l N o G . S r u c r n ( 1 9 2 8 ) D e h y d r a t i o n a n d o p t i c a l
study of alunogen, nontronite, and griffithite. Am. J. Sci. 15,
We wish to thank Professor
Cesbronfor providingthe alunogen
l-19.
crystals.
LAUSEN,CARL (1928) Hydrous sulfates formed under fumerolic
c o n d i t i o n sa t t h e U n i t e d V e r d e M i n e . A m . M i n e r a l . 1 3 , 2 0 3 - 2 2 9 .
References
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mination of centrosymmetric
crystalstructures.ln, F. R. Ah- O H v l , Y . ( 1 9 7 0 ) " F o R D y , " U n p u b l i s h e d C o m p u t e r P r o g r a m .
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Denmark,p 58-62.
. of Dana, Tth ed., Vol. 2. John Wiley and Sons,
Copenhagen,
Mineralogy
lnc., New York.
Cnourn, DoN T., M. L K,rv, ANDA. C. L,rnsoN(1967)Refinementof the alum structuresII. X-ray and neutrondiffractionof R o B r N s o N ,P . D . , e r o J . H . F n ' r c ( 1 9 7 3 ) C r y s t a l s t r u c t u r e sa n d
NaAI(SOa),l2H2O,1 alum.Acta Crystallogr.22,182-187.
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-,
ANDJ. B. MANN(1968)X-ray scatteringfactorscomputed
structure of kornelite. Am Mineral. 58, 535-539
( 1 9 7 4 ) " S y r ' l s n o , " U n p u b l i s h e dC o m p u t e r P r o g r a m .
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Snrrs, N. O. (1942) The hydration of aluminum sulfate. J. Am.
Acknowledgment
(1969)"Wrlxonn," UnpubFerc, J H., lNn P. D. Rosu.rsoN
Chem Soc. 64,4l-M.
lishedComputerProgram.
Tsone.s, J., P. D. RontNsoN, eNo J H. FeNc (1974) Crystal
-,
(1970)Crystal structuresand mineralchemANDstructures and mineral chemistry of hydrated ferric sulfates. IV.
istry of hydratedferric sulfates.I. The crystalstructureof coThe crystal structure of quenstedtite.'4m. Mineral.59' 582-586.
quimbite.Am. Mineral.55, 1534-1540.
W u r n s c H , B . J . , l N o C . T . P n p w r r r ( 1 9 6 5 ) C o r r e c t i o n sf o r X - r a y
L. W. (1969)The crystalstructureand cationdistribution
absorption by a crystal of arbitrary shape Z. Kristallogr 122,
FINGER,
of a grunerite.Mineral.Soc.Am. Spec.Pap.2, 95-100.
24-59.
Hrxnv, J. L., nun G. B. KlNc (1949)The systemaluminum
sulfate-sulfuricacid-water at 60oC. J. Am. Chem.Soc. 11,
Manuscript receioed, April 21, 1975; accepted
n42-|L44
for publication, August 22, 1975.