AmericanMineralogist, Volume64,pages337-351, 1979
High-temperature
crystalchemistryof hydrousMg- andFe-cordierites
MrcHeelF. Hocssr_r_e,
Jn.r
Departmentof GeologicalSciences
Virginia PolytechnicInstitute andState [Jniuersity
Blacksburg, Vi rginia 2406I
GoRpoNE. BnowN,Jn.
Departmentof Geology
Stanford Uniuersity
Stadord, Califurnia 94305
FneoK. RossnNoG. V. Grsss
Departmentsof Chemistryand GeologicalSciences
Virginia PolytechnicInstitute qndState (lniuersity
Blacksburg, Vi rginia 2406I
Abstract
Structuralrefinements
havebeencompletedfor a Mg-rich cordieriteusingdatarecordedat
24",375o,775oand 24"C (afterheatingto 775")and for an Fe-richcordieriteat 24" and
375'C. The meanT-O bond lengthsin both cordieritesremainunchangedbut the mean
octahedralbonds(M-O) lengthenupon heating.The unusuallylow thermalexpansionof the
Mg-cordieriteis the resultof its relatively"rigid" tetrahedralframeworkand the anisotropic
expansionofoctahedraisolatedfrom eachother.This anisotropicexpansionleadsto a slight
rotation of the six-membered
rings,a concomitantcollapseof the structureparallelto c, and
an expansionparallel to a and 6. In the Fe-cordierite,the octahedronis more flattened,
resultingin c being smaller and a and b being larger than the cell dimensionsof the Mgcordierite.Upon heatingFe-cordierite,thereis no evidencefor a rotation of the rings,and a,
b, and c increaseas the M-O bondsexpand.
X-ray Ap mapscalculatedfor the Mg-cordieriteshowedapproximatepositionsand relative
amountsofchannelconstituents.
The peakascribedto the alkali and other atomsthat centers
the six-membered
rings becomeselongatedparallelto c upon heatingthrough 375.c. However,the peakascribedto the oxygenassociated
with HrO in the 24' and 375' mapsis absent
in the 775'C maps.It reappearsin mapscomputedfrom the 24" (afterheating)data.In both
cordierites,small amountsof hematitewere producedduring heating(prematurelyhalting
data collectionon the Fe-cordierite),and apparentlyformed by combinationof octahedral
and channeliron with oxygenfrom the channelwater molecules.
A re-examination
of the water-orientation
in the channelso[ the Mg-cordieriteusing
neutronand X-ray Ap mapsdoesnot clearlyshoweithertype I [H-o-H in the (100)plane
with the H-H vectorparallelto cl or type II [H-o-H in the (100)planewith the H-H vector
parallelto b] water, as previouslysuggested
by spectroscopic
studies.Instead,our ap maps
indicatethat the watermoleculeliesin a planetilted -29o from (100)and that the H-H vector
is tilted -l9o from c.
Introduction
its widespreadformation in moderate-to high-grade
cordierite,(Mg,Fe)rAlaSiuO,r.
nHrO, hasattracted metamorphicrocks, its occurrencein a variety of
the interestof mineralogistsand ceramistsbecauseof structuralstatesinvolving differentdegreesof AllSi
ordering,and its unusuallylow thermalexpansion.
I Presentaddress:Department
of Ceoloqy,StanfordUniver- Ceramistshave found a number of applicationsfor
sity, Stanford,California94305.
Mg-cordieriteas a thermal shock resistantmaterial.
w3-n4x/79/0304-0337$02.00
317
HOCHELLA ET AL,: CRYSTAL CHEMISTRY OF CORDIERITES
Among theseare useas an insulatorfor sparkplugs,
as a refractorycoating on metals for internal combustionengines,in the productionof dolomitic types
of refractoriesand low-expansionconcrete,and as a
catalyticsupport for the treatmentof wastegas and
automobileexhaustemissions.
Perhapsits most important applicationin the future will be in the fabrication of turbine engines(Gostelowand Restall,
1972).Fe-richcordieritehas beenproducedin industry but only as a by-productin blast-furnacelinings
(Richardson, 1949),in "black cores" in stoneware
pipe (Lach, 1974),and evenin building-brick(Rathgeberand Fowler, 1966).Becauseit is more difficult
to synthesizethan Mg-cordieriteand becauseit oxidizes at high temperatures,ceramistshave not yet
found specificapplicationsfor Fe-rich cordierite.
Despitethe extensiveuse of Mg-cordieritein the
ceramic industry and the growing geologicimportanceof both the Mg- and Fe-richphases(see,e.g.,
Currie,1971;Newton,1972),
no detailedstudyof the
behaviorof the cordieritestructureat high temperatureshas been undertaken.The presentstudy (see
Hochella,1977)wascarriedout in orderto determine
the crystal structuresof hydrous Mg- and Fe-rich
cordieriteas a function of temperature,in an attempt
to clarify the unusual thermal-expansion
properties
of this mineral. Also, the effectsof heatingon both
the channelconstituentsand the AllSi distributionin
the tetrahedralframeworkwereinvestigated.
Finally,
the neutrondiffractiondataofCohenetal. (1977)for
the White Well cordieritewere re-analyzed,
and the
orientation of the water moleculeswithin the channelsof this structureis discussed.
Dolni Bory cordierite,wascollectedfrom a pegmatite
near Dolni Bory, WesternMoravia, Czechoslovakia
(Stanekand Miskovsky, 1964),where crystalsare
reportedto attain dimensionsup to severaldecimeters. Many singlecrystalsweresector-twinned;however, one exhibiting uniform optical extinction was
found suitablefor structuredetermination.This crys0.33X 0.33X
tal wasa nearlyequantchip measuring
0.27 mm. After orientation by optical spindle-stage
techniques(Bloss, in preparation), crystals of the
White Well and Dolni Bory cordieritesweremounted
fimullite cementon silica-glass
in high-temperature
capillariesto
bersand sealedin evacuatedsilica-glass
inhibit the oxidation of iron. Each was heatedfor
approximately12 hours at l00oC to cure the cement
and was then equilibratedfor at leastl2 hours at the
temperatureof the measurementbeforedata collection was begun. Temperaturefluctuations for the
single-crystalheater(seeBrown et al., 1973,for details) were recordedcontinuouslyon a strip chart
during each high-temperatureexperimentand were
not morethan t l0o.
Thermalexpansionmeasurements
Cell parametersfor the White Well cordierite at
seventemperaturesranging from 24" to 775o and
againat24"C afterheating(seeTable2) weredeterrefinementof the diffractomemined by least-squares
Table l. Cell parameters(24"C), distortion index (A), specific
gravity,calculateddensity(p) and compositionof the White Well
and Dolni Bory cordierites
Lrhite
Experimentaldetail and observations
a
b
c
A
s .g .
p (calc. )
Specimendescriptions
The Mg-rich cordierite,designatedthe White Well
cordierite, was previously describedand used in a
combined X-ray and neutron diffraction study by
Cohen et al. (1977).It occursin a phlogopiteschist
which formed under amphiboliteto granulite facies
conditions(Pryce,1973)and is one of the most Mgrich specimensyet reported (seeTable l). We assumedthat our crystal(0.30X 0.22X 0.22mm) and
thoseusedby Cohenet al. (1977)had identicalchemical compositionsand crystalstructuresbecausethey
had statistically-identicalcell dimensionsand were
selectedfrom the samespecimen(an approximately
4-mm cube). The room-temperatureintensity data
(beforeheating)weretakenfrom Cohen(1975).
The Fe-rich cordierite (Table I ), designatedthe
2
Formulae
Alkalis
M cations
liell
1 7 . 0 8 8( 3 ) 1
9.734(2)
9.359(1)
0.25"
2,51
2.56 e/ cmr
Dolni
Bory
r z . z : o ( s )i
9.83s(3)
9. 3 r 4 ( 3 )
0.21'
2.76
2.78 g/cn3
(based on 18 oxygens)
.z
" t o . o 5 * 0 .o 2 c " o o
"oo. ot'rr. rt"93lo,
Nto.
15c"0.o5
otto.ou"ro.,rt"i]u,
T cations
si5.otA13.9:
si4. rAr4.
9
05
iJater
(HZO)
(Hzo)o.ot
O. SO
1 The nwnbex in parentheses ?epresents the stmdard
resoqLated utth the Last decinal place reported.
2 Whtte WeLL cordierLte
Dolni Borg cordierLte
MLskoxsky (L964).
eruor
(lG )
eorrposition repoxted by Prgce (1973);
eontposition reported by Stanek md
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERITES
Table2. Cell edges(A), cellvolume(As),and calculateddistortion
index (A) Dr temperaturefor White Well and Dolni Bory
corolerltes
Tenperature
Whlte Well
("C)
a
cordlerlt€
24
280
375
470
r z . o s s( : ) 1
17.103(3)
17.1r.3(3)
77.123(2)
9.734(2)
9.737(2)
9.741(r)
9.745(7)
9.359(1)
9.357(1)
9.358(1)
9.357(r)
7 5 5 6 . 7( 4 )
1558.2(4)
1550.0(3)
156r.3(3)
O.25
O,26
0.21
O.27
r 1. L 3 2 ( 2 )
r 7. k o ( 2 )
r7 .t49(2)
17.119(2)
9.751(1)
9.755(r)
9.7s9(1)
9.746(r)
9.357(1)
9.355(1)
9.352(r)
9.36r(1)
1563.1(3)
L564.2(3)
1565.1(3)
1561.8(3)
O.27
0,27
O.27
O.26
17.230(5)
r7.2s8(3)
9.835(3) 9.3r4(3)
9.847(2) 9.328(2)
1578.3(8)
1 5 8 5 . 3( 3 )
0.21
0.22
7 rh.e
in pare,ntheee|,
,lweere
oI tne L@t @dML
qwted
2 Afte"
represent
the eetinated.
stadzyd.
ewt
(t6)
heatirg
ter settingsanglesfor 28 reflectionsin the 20 range
30-40". Similar refinementswerecarriedout for the
Dolni Bory cordieriteusingdata gatheredat 24" and
375'C. The refinedcell parameters,cell volume,and
calculateddistortion index (Miyashiro el al., 1955)
for eachtemperatureare listed in Table 2.
Data collectionand refinements
Intensitydata from oneoctantof the MoKa sphere
werecollectedover a rangeof 5" to 60' 20 at temperaturesof 375o,775o, and,24"C (after heating)using
graphite-monochromatized
MoK radiation (White
Well cordierite)and at 24" and 375oCusing Zrfiltered MoK radiation(Dolni Bory cordierite)r.The
upper 20limit was imposedby the heaterconfiguration. Two standardreflections(060 and 008) measuredevery30 reflectionsindicatedthat machinedrift
and/or crystalmovementwerewithin acceptable
limits, so no drift correctionswere applied.Observed
intensitiesfor the White Well cordierite were correctedfor Lorentz-polarizationeffectsassuminga 50
percentideally mosaic monochromatorcrystal and
were convertedto lF(obs)l with a valuesestimated
using the equationof Corfield et al. (1967).The observedintensitiesfor the Dolni Bory cordieritewere
correctedfor Lorentz-polarizationeffectsand convertedto lF(obs)l with the programDereI-rss.Ab'zIntensity data for the White Well
cordierite were collected at
Stanford University; data for the Dolni Bory cordierite were collected at VPI and SU.
8 Catalogued in the World List of
Crystallography Computer
Programs (3rd edition).
339
sorption correctionswere not initially applied to either the White Well (p : 9.0cm-') or Dolni Bory (p
: 26.3 cm t) cordieritedata setsfor the following
reasons:(l) Positional parametersobtained from
both X-ray and neutron refinementsfor the White
Well cordieriteof Cohenet al. (1977)are identicalto
within 26; the X-ray data were uncorrectedfor absorption.(2) The relativelylow linear-absorptioncoefficientand sizeof the White Well cordieritecrystal
usedin this studyresultin a differentialabsorptionof
about7 percentin theworstcase.(3) The Dolni Bory
crystalwas dislodgedand lost from its mount before
its shapewas accuratelydetermined.However,the
crystal was nearly equant and, in the worst case,
produceda differencein transmissionof - l6 percent.
After completionof this study, an absorptioncalculation for the White Well cordieritecrystalwasmade
usingthe programAcNosr written by Coppensel a/.
(1965),which showedthat transmission
variedfrom
0.84to 0.90.Thus our neglectof an absorptioncorrection in this case should not result in significant
errorsin positionalparameters.
In the caseof our Ferich cordierite,whereabsorptionis more significant
(transmissionis predictedto vary between0.42 and
0.49in the worst cases),the roughly equantshapeof
the crystalwould resultin a differentialabsorptionof
l0 percentor lessbetweenmost pairs of reflections.
Furthermore, the bond lengths from the two Fecordieriterefinementsare quite reasonable
relativeto
the Mg-cordieritedistances,suggestingthat the Fecordierite positional parameterswere not significantly affectedby differentialabsorptioneffects.
An approximateextinction correction was made
and least-squares
refinementswere calculatedwith
first isotropicand later anisotropictemperature-factor models.Weightsbasedon the countingstatistics
were used in all refinements,and reflectionswere
automaticallyrejectedat the 2& level for the White
Well cordieriteand at 3,i for the Dolni Bory cordierite. In our refinementof theWhite Well cordierite,we
neglectedthe channel constituentsreported in the
chemicalanalysis(Table l). On the other hand,while
neglectingthe water,we includedthe alkali atomsin
our refinementfor the Dolni Bory cordieritebecause
of their greaterabundance.The number of accepted
reflectionsand the weightedand unweightedR factors for the anisotropicrefinements
aregivenfor both
cordieritesin Table3. The final positionalparameters
and anisotropictemperaturefactors, as well as the
isotropicequivalenttemperaturefactorsfor the nonequivalentatoms in the White Well and Dolni Bory
cordierites,are listedin Table4. Observedand calcu-
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERITES
for the White Well
Table 3. Resultsof the aniSotropic
refinements
and Dolni Bory cordierites
Cordierlte
TeEDeralure
whire Well
24"c Taftet
C o h e ne t a L . ,
1977)
375"C
R-factor
IJNII'
'd2
1 0 57
0.033
0.051
L07 7
0.041
0.066
994
0.056
0,087
24"C (afxer
heating)
LL7 6
0,038
0.061
24'C
1203
0.073
0.063
7L6
0.061
0.063
175"C
Dolni Bory
/I of accepted
reflectlons
375"C
R@M) = ttlrel - lrolltllFol
2 R < w )= t L u ( l F o l - l r . l ) ' / t n { r ; ' l \
r
loss in the intensitiesof the diffractiondata nor evidenceof oxidation or breakdown.However,unlike
cordierite,both of thesemineralslack loosely-bound
water moleculesand Fe atomsin the channels(Goldman et al., 1977).Upon heating,thesecomponents
apparentlyreactto producehematiteevenin a thoroughly evacuatedcapillary. The decreasein the intensitiesof the diffractiondatarecordedfor the Dolni
Bory cordierite indicatesthat octahedralFe is also
involvedin the reactionto form hematite,which results in partial disruption of the Fe-cordieritestructure.
Discussion
Axial expansion
The a cell edge of the White Well cordierite increasesas a function of temperatureat a rate slightly
greaterthan that of 6, while c undergoesa slight but
lated structurefactorsare given in Table 5.4Selected systematic
shorteningup to 775oC(Fig. l). On the
interatomic distancesand angles uncorrectedfor other hand, the c cell edgeof the Dolni Bory cordierthermal motion were calculatedwith the program ite (not plotted) doesnot shortenupon heatingfrom
ORnnes
and are givenin Table6.
at aboutthe samerateas
24" ro 375'C but increases
photographsof the White Well cordier- the a and b cell dimensions.However,becauseall
Precession
ite recordedfollowingthe heatingexperimentshowed parametersof the Dolni Bory cordieritewere deterpowder rings of weak intensityidentifiedas the dif- minedat only two temperatures
up to 375"C (Table
fraction pattern of hematite.Later, when the Dolni 2), the variation of theseparametersand cell volume
Bory cordieritewas heatedabove600"C, the crystal with temperatureis only qualitativelyknown over a
changedfrom colorlessto amber while the peak in- relatively small temperaturerange. Therefore,the
tensitiesdropped off drastically,preventingthe col- ratesof axial and volumeexpansionfor the two corlection of additional data. A secondcrystal was se- dieritescannotbe quantitativelycompared.
lected and the measurementswere repeated,but
Thermal expansiondata for the disorderedpolyagain the peak intensitiesdropped off markedly at morph, indialiteu(P6/mcc), measuredby Fischeret
photographsre- al. (1974)and by Lee and Pentecost(1976),are comtemperatures
above600o.Precession
showed paredwith thosefor the orderedWhite Well cordiercordedafter the secondset of measurements
the samefaint powder rings of the hematitediffrac- ite (Cccm) in Figure l The expansionof the a cell
tion pattern.Rathgeberand Fowler (1966)carried edge of White Well cordierite is about l500ppm
out open-air heating experimentsat I150" on greater at 775o than that of indialite, whereasthe
stoichiometricFe-cordierite,in which they noticeda expansionalong b in the former is practicallythe
reddeningof the crystals,a 40 percent decreasein same as that along a in the latter. The contraction
measuredX-ray powder diffraction peak intensity, along c in White Well cordieriteis significantlyless
and the formation of hematite(seealso Stunz et al., (-800ppm lessat 775")thanthat alongc in indialite.
CaFeSizOe, Moreover,the variation of c in White Well cordierite
1971).On the other hand,hedenbergite,
was heatedwithout oxidation as high as 1000' for is linearwith temperaturewithin the limits of error of
data collectionby Cameron et al. (1913),using the the results.The thermalexpansionmeasurements
for
sameheater and mounting techniquesemployedin the two indialitesshowan initial contractionalongc
our study.Brown and Prewitt(1973)heatedan oli- with temperature,but Fischeret al. find that c begins
capillarywith no
vine(Far')to 7lOoCin an evacuated
{ To receivea copy of Table 5, order DocumentAM-79-093
from the BusinessOffice,MineralogicalSocietyof America, 1909
K Street,N.W., Washington,D.C. 20006.Pleaseremit $1.00in
advancefor the microfiche.
u Cordierite may exist in a range of structural states,like alkali
feldspars, depending on the ordering of Al and Si in the tetrahedral framework. The ordered form of cordierite is orthorhombic;
the completely disordered form is hexagonal and has been given
the name indialite.
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERTTES
341
Table4. Final fractionalcoordinates
and thermalparameters
(X 106)for White Well and Dolni Bory cordieritesat varioustemperatures
f
Aron
24.cr
v
z
Brr
Bzz
0
rl2
Ll4
3 9( 3 )
1 4 6( r 0 )
e 8( 1 0 )
0
0
0
o.45
0
rl2
Ll4
60(s)
245(r5)
228(L7)
0
0
0
0.81
0
L/2
Ll4
88(7)
352(22)
342(25)
0
0
0
1 .1 9
0
Ll2
rl4
3 3( 4 )
L70(L2)
1 3 5( 1 5 )
0
0
0
0 .5 0
0 . 1 9 2 6( 1 )
(1)
0.0778
0
3 8( 2 )
83(7)
1 1 8( 8 )
7( 3 )
0
0
0.39
0 . 1 9 2 0( 1 )
0 , 0 7 8 3( 1 )
0
60(4)
lss (11)
2 3 9( 1 1 )
1 1( 5 )
0
0
0 .7 1
0 . 1 9 1 7( r )
0 . 0 7 8 s( 2 )
0
8 7( 5 )
2 4 0( 1 5 )
373 (20)
13(7)
0
0
1.08
0 . 0 s 0 8( 1 )
0.3079(1)
0
3 1( 3 )
1 2 1( 8 )
r32(9)
8(3)
0
0
0.43
0 . 0 5 0 6( 1 )
0 . 3 0 7 6( 1)
0
62(4)
220(L2)
2 6 8( 1 5 )
2L(5)
0
0
0.83
0 . 0 5 0 0( 1 )
0.3070(2)
0
9 1( 6 )
3 3 s( 1 8 )
382(22)
2 7( 8 )
0
0
t.23
z
B rr
Bzz
B ss
Brz
Brs
Bzr
eq
x
v
z
B rr
Bzz
B sg
Btz
B rr
Bzt
B
eq
x
v
z
T ? 3( S i )
B rr
Bzz
B :.
pr 2
Brs
8zr
B
X
v
o-r I
Brr
8zz
B::
B rz
B rr
Bzz
B
eq
x
v
z
grr
0r . 6
Ll4
Il4
0.2502(r)
s 1( 3 )
1 0 6( 1 0 )
1 74 ( r 2 )
1 5( 4 )
0
0
o.54
x
v
z
B rr
Bzz
Bs:
Brz
Brs
Bzz
B
v
T 1 6( A l )
-
Ll4
rl4
0.2s00(2)
r25 (6)
3 6 3( 1 9 )
429(22)
3 s( 8 )
0
0
7.46
2 4 "c 2
Brz
B rs
Bzz
Br
R^ ^
Trl(Si)
-
rl4
rl4
0.2s00(2)
9 3( 4 )
224(r2)
2 72 ( L 4 )
22(s)
0
0
0 .9 5
7 75 " c
s 7( 3 )
1 3 3( 8 )
1 1 0( 9 )
1 s( 3 )
0
0
o.52
rrl (A1)
1 1 6( s i )
Ll4
L/4
q
0 . 2 5 0 2( 1 )
375.c
2
p 3,3,
Brz
Brs
Bzz
B
eq
DolniBory
24"C (Cem\
375oc
Ll4
Ll4
o.2502(3)
4r(6)
1 0 4( l s )
6 4( 1 s )
L4(7'
0
0
0.37
0
Ll2
rl4
rl4
0 . 2 s 0 1( 4 )
94(e)
208(28)
L04(26'
3 8( 1 2 )
0
0
0.80
0
0.33
0
Lt2
Ll4
u (10)
2L9(34)
1 4 4( 3 s )
0
0
0
0.52
0 . 1 9 2 4( 1)
0 . 0 77 8( 1 )
0
32(3)
9r(9)
167(r2)
1(4)
0
0
0.44
0 . 1 9 0 1( 1 )
0 . o 19 4 ( 2 )
0
3 7( 6 )
3 8( 1 4 )
64(L7)
L2(7 )
0
0
0.31
o . L 8 9 4( 2 )
0.079s(3)
0
6 5( e )
L44(25)
D,7 (29)
4(L2)
0
0
0.58
0 . 0 5 0 8( 1 )
0 . 3 0 79 ( 1 )
0
3 2( 3 )
1 2 4( 1 0 )
1 s 3( 1 3 )
o.46
0 . 0 s 0 1( 1 )
(2)
0.3076
0
33(7)
64(L6)
6 9( 1 9 )
1 3( 8 )
0
0
o.29
o . 0 4 9 9( 2 )
0 . 3 0 7 7( 3 )
0
4 3( e )
L62(28)
208(32)
3 9( 1 3)
0
0
0.62
- 0 . r 3 s 2( 1)
o . 2 3 74 ( L )
0
23(3)
1 3 3( 9 )
1 4 1( 1 1 )
_ 1 3( 4 )
0
0
0.44
-0.1347(1)
0.2343(2)
00
34(7)
4 3( 1 s )
73(16)
-22(7)
00
00
o.28
-0.1350(2)
0.2344(3)
s( 4 )
0
r/4
3 r( 8 )
L22(20)
44(2o)
0
- 0 . 1 3 5 2( 1)
o . 2 3 75 ( r )
0
3 7( 2 )
9e(7)
1 0 5( 8 )
-1r(3)
0
0
0.39
- 0 . 1 3 5 1( 1 )
0 . 2 3 6 9( 1 )
0
5 7( 4 )
176(11)
247G3)
-L4(4)
0
0
0.73
- 0 . 1 3 4 7( r )
o . 2 3 6 3( 2 )
0
8 6( 5 )
273 (16)
3 4 0( r 9 )
- 4 0 ( 7)
0
0
1.08
o.247
4(r)
0 . r 0 2 9( 1 )
0 . 1 4 1 0( 2 )
74 ( 5 )
ls3 (13)
179(15)
-31(6)
_ 1 9( 1 1 )
0.69
o . 2 4 70 ( L )
0 . 1 0 3 6( 2 )
0 . 1 4 0 7( 3 )
L 3 7( 7 ) '
2 7 7( 2 2 )
3 0 8( 2 5 )
2 4( e )
-40(11)
_ 6 8( r 9 )
L.25
o . 2 4 6 8( 2 )
0 . 1 0 4 2( 3)
0 . 1 3 9 8( 4)
2L7(L2)
4 1 4( 3 6 )
4 s 0( 3 8 )
1 6( 1 6 )
-r22(L9)
-95 (29)
1 .9 0
0 . 2 4 7 3( r )
0 . 1 0 3 4( 2)
0.1409(2)
6 6( s )
282(16)
1 5 3( 2 0 )
3( 8 )
-31(8)
- 1 1( r 6 )
0 . 79
0.2442(2)
0 . 1 0 s 2( 3 )
0 . r 4 1 5( 3 )
69(r2)
r29 (27)
9 3( 2 8 )
-15(r4)
-44(t6)
-34(24)
0 .5 5
0.2438(3)
0 . 1 0 4 9( 5)
0 . 1 4 1 2( s )
1 0 1( 1 6)
296(52)
269(56)
1 8( 2 3 )
-80(26)
-40(44)
1 .1 0
0 . 0 6 2 0( r )
0 . 4 1 6 0( 2)
o.L5r2(2)
s 4( 5 )
2 1 1( r 3 )
1 8 0( r 5 )
r7(6)
-2(6)
-7r (1r)
0.69
0.0620(1)
o . 4 1 6 6( 2 )
0 . l s r 2 ( 3)
90(7)
3 75 ( 2 L )
33r(25)
24(Lo)
-16(11)
- r s 0 ( 1 9)
L.2L
0 . 0 6 1 9( 2 )
0 . 4 1 5 9( 3)
0 . 1 5 1 0( 4)
1 2 2( 1 0 )
ss0(33)
s 4 s( 3 9 )
2 3( L 6 )
-73(r7)
-234 (32)
0 . 0 6 2 3( 1 )
o.4166(2)
0.1513(2)
s 7( 5 )
2 t s ( r 7)
1 e 8( 2 1 )
-3 (8)
1 0( 8 )
-7 2 (r5)
0 .7 3
0 . 0 6 1 1( 2 )
o . 4 L 4 4( 4 )
0.1522(4)
70(12)
207(29)
1 3 4( 3 3 )
3o ( 1 4 )
23(L6)
-s8 (26)
0 .6 9
0 . 0 6 0 9( 3)
0 . 4 1 s l( s )
0 . 1 s 0 9( 5 )
9 s( l s )
324(48)
2 8 5( 6 0 )
23(23)
-18(25)
-13r (46)
1.13
e(s)
l. 6r
s9(9)
r 5 1( 2 6 )
140(28)
-r2(r2)
0.59
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERITES
342
Table4. (continued)
Dolni
Whlte well
Arom
24"Cr
- 0 . 1 73 2( 1 )
0 .3 r 0 r(2 )
0 . 1 4 1 6( 2 )
s4(4)
2o2(L4)
1 9 9( l s )
= 1 1( 6 )
2 0( 6 )
-29(11)
0.70
v
z
Brr
Bzz
o r3
p33
Brz
Brs
9zs
B
eq
x
v
Brr
Bzz
Bg:
9rz
Brc
9zs
B
ozL
eq
x
z
Brr
Bzz
Bsr
Btz
Frs
Bzg
B
eq
oz6
x
oz3
375"C
z
Brr
Bzz
B :s
Brz
Brg
Bzs
B
eq
0 . r 2 2 3( 1 )
0 . 1 8 3 9( 2 )
0
70(7)
248(2L)
3 8 6( 2 s )
sl(9)
0
0
1.04
0 . 1 2 2 0( 2 )
0 . 1 8 4 6( 4 )
- 0 . 0 4 3 0( 1 )
0 . 2 4 76 ( 2 )
0
s 3( 7 )
3 0 1( 2 1 )
330(24)
-27(9)
0
0
0.97
-O.0434(2')
0 . 2 4 7I ( 4 )
0
6 9( 1 1 )
s 9 4( 3 9 )
7 1 1( 4 9 )
-31(15)
0
0
1.85
- 0 . 1 6 4 5( 1 )
o . 0 79 2( 2 )
0
el(7)
144(19)
36L(23)
-37 (9)
0
0
0.96
- 0 . 1 6 4 1( 2)
0 . 0 79 3( 3)
0
1 6 3( 1 2 )
1 8 9( 3 0 )
7 7 9( s o )
- 7 6( l s )
0
0
L . 79
1 3 s( 1 2 )
3 6 8( 3 5 )
7 1 8( s 0 )
1 3 3( 1 6 )
0
0
r. 83
0 . 1 6 2 s( 1)
Ll2
x
v
u4
z
Brr
4 8( 3 )
L42(9)
18r(9)
0
0
0(7)
0.58
R^-
B:s
Btz
Brr
Bzs
B
eq
I
ALL 24"c data fron
2
A|ter
3
B"o i.e the isotropic
(HdniLton,
L969)
cohen et aL.
0.70
0 . 1 2 2 2( 2 )
0 . 1 8 4 4( 3 )
0
7 3( 8 )
1 7 8( 2 s )
4 0 1( 3 6 )
6 1( 1 2)
0
0
0.98
0 . 1 1 8 8( 3)
0 . 1 8 2 2( 6 )
0
72(2o)
L 76 ( 4 5 )
4O4(64)
66(20)
0
0
o.97
0 . 1 2 0 0( 5 )
0 . 1 8 3 3( 8 )
0
r37 (27)
270(78)
702(r09)
1 0 9( 3 8 )
0
0
L.7r
-o.0432(2)
o . 2 4 8 7( 3 )
0
5 8( 8 )
26r(2s)
3 6 0( 3 4 )
-33(12)
0
0
0.98
- 0 . 0 4 3 s( 4 )
0 . 2 4 4 9( 6 )
0
4 0( 2 0 )
3 6 3( 5 6 )
4e4(66)
-16(25)
0
0
L.20
- 0 . 0 43 4( 4)
0.2462(9'
0
s 6( 2 s )
5 7 9( 9 4 )
6 0 7( r 0 1 )
- 1 0 7( 3 8 )
0
0
r.o/
-0. r630(3)
0.0778(s)
0
243(20)
298(45)
850(70)
-lss (2s)
0
0
2.32
-0.L646(2)
o . 0 8 0 3( 3)
- 0 . 1 6 1 5( 4)
0.0778(5)
0
9 0( 1 9)
1 0 1( 4 0 )
3 8 2( s 9 )
7 (22)
-o.L607 (7)
0.o766(7)
0
1 9 0( 2 9 )
lls (70)
6 2 1( r 0 4 )
- 6 9 ( 3 s)
0
0
0 . 1 6 2 6( 1 )
rl2
Ll4
1 0 9( 7 )
3 8 5( 2 0 )
655(26)
0
0
3 0( 2 0 )
1.68
0 . 1 6 2 4( 1 )
-39(rs)
0 . 1 2 1 6( 3 )
0 . 1 8 4 3( 6 )
0
1 6 s( 1 8 )
6 1 5( 5 9 )
L2O6(94)
2r7 (27)
0
0
a
o.t622(L)
rl2
Ll4
75(4)
259(r4)
436(L6)
0
0
I (12)
1 .t 3
375"c
- 0 . r 7 2 9( 3 )
0 . 3 0 4 9( s )
0 . L 4 2 1( 5 )
6 5( L 7)
4 s 4( s 6 )
254(60)
-45(23)
46(22)
_25(4s)
1. 1 4
- 0 . r 1 2 9( 2 )
0 . 3 0 5 3( 4)
0.L428(4)
8 o( 1 3)
r86(30)
e 4( 3 0 )
-2L(L4)
3(1s)
-84 (2s)
o.67
- 0 . 1 73 3( 1 )
0 . 3 1 0 2( 2)
o . L 4 L 4( 2 )
60(s)
L 74 ( L 7)
2O9(2r)
- 2 0 ( 8)
2 1( 8 )
- 0 . r 7 3 4( 2 )
0 . 3 0 8 2( 4 )
0.1422(4)
L79(L2)
5 0 1( 3 s )
s49 (42)
- s s ( 1 7)
9 5( 1 8 )
- 1 4 0( 3 2 )
1.98
- 0 . 1 73 6( 1 )
0 . 3 0 9 0( 2 )
o . 1 4 1 8( 3 )
1 1 1( 7)
342(22)
285(25)
-26(r0)
3 6( 1 0 )
-90(19)
L.20
BorY
24"c (Ccm)
24"C2
775'C
Q1
- 0 . 0 4 3 8( 3 )
0 . 2 4 8 4( 6 )
0
L22(L7
)
8 8 3( 6 9 )
87s(76)
" -L4<26)
0
0
2.62
8 8( 8 )
r4o(2s)
4L2(35)
-2(r2)
0
0
1.00
0
0 .9 3
L.OZ
0 . r 6 3 2( 1 )
t/2
Ll4
4 7( 4 )
1 1 e( 8 )
L62(9)
0
0
1 2( 1 0 )
0.53
Uz
rl4
4 4( 3 )
L22(rr)
22s(t3)
0
0
5(L0)
0 .5 9
0 . 1 6 3 2( 1 )
Ll2
rl4
80(5)
2 5 6( l s )
4 0 2( 1 8 )
0
0
11(17)
1 .1 1
(L97?)
heating
equiualent
of
the anisott'opic
Beq = 4/a
l\tta2
tqnperaAne
*
factore
cdlcul'ated
using
the
erp"easion
Bzzb2 + Bzsc2 * 2Btzabcos(
* 2\zgbccosd + 2Br3accosg\
a
The ntmbete
reported.
in
parenthesis
pefe"
to
the
estinated
sta/tdard
ernor
(tG)
associ.ated
dith
the
Laet
decinnl
pLace
HOCHELLA ET AL..' CRYSTAL CHEMISTRY OF CORDIERITES
343
Table6. T-O and M-O interatomicdistances
(A) and O-T-O angles(') for the five tetrahedralsitesus.temperaturein White Well and
Dolni Bory cordierites
Illlite
Distance/
Ansle
T11-011
MultiDlicity
I2l
12l
;:*'
013"-T11-O13|
o11-Tr1-o13"
-ot3'
-otl'
t1l
I2)
t2l
tr1
!1ean
u';l:l
016-T16-o16,
-ot6 "'
t4l
t2l
l2l
t2l
"""r-otu"
T21'01l
-o23'
t2l
tll
tll
;:::
orl -Tr1-orlm
-ozL
-oz3'
"';]:l-"''
T23-013
-oz3
tll
t21
tzl
111
I2l
t1l
t11
;:::
0r3-Tr3-0r3n
-o
z6
'oz3
o'u;l:l-""
T26-0L6
-ozL
t1l
I2l
t-21
t11
t-21
tll
tll
;:::
or6-Tr6-or6m
-oz6
-ozL
o2l-T26-026
t1l
12l
L2l
trl
Mean
T2I-OzL-T26
T
2L-O23-'r23
T23-O26-T26
l2l
t2l
l.2l
24"C
375"C
Dolni
well
175"c
775?ct
24"C2
24"C
Bory
375"C
t.760(2)
L.756(2)
1.7s8(3)
L.75s
r.758(2)
L,748(4)
1.756(s)
L.757(2)
L.75r(2)
1.751(3)
L.162
L.7il.(2)
L.748(4)
1.750(5)
1.7s8(1)
1.753(1)
r.754(2)
L.759
1.759(1)
t.748(2)
1.7s3(3)
109.6(1)
109.3(2)
109.6(3)
r-09.0
10e.6(1)
110.4(3)
110.3(4)
9 4 . 1( L )
9s.3(1)
95.6(2)
95.3
94.8(1)
96.9(2)
1 2 5 . 9( 1 )
L24.6(r)
L25.2(2)
L25.4
1 2 5 . 9( 1 )
t 2 2 . 7( 2 )
L22.4(2)
109.0(1)
108.7(2)
r80.2(2)
10e.3
108.8(2)
1 0 9 . 3( 2 )
1 0 9 .3 ( 4 )
110.0(r)
110.0(1)
109.9(1)
109.9
110.0(1)
109.8(1)
109.8(1)
I.626(2)
L.62s(2)
1.631(3)
L.626
L.628(2)
r.627(4)
1.631(5)
L.626(2)
r.62s(2)
1.631(3)
L.626
r,628(2)
r . 6 2 7( 2 )
r . 6 3 1( 3 )
119.7(1)
r20.0(2)
119.6(3)
119.s
120.0(1)
lr7.6(3)
118.3(4)
110.i(1)
110.6(2)
110.7(3)
110.8
110.8(1)
lr1.9(3)
110.9(4)
98.7(1)
98.s(2)
98.7(2)
98.8
98.2(1)
109.7(1)
109.7(1)
r09.7(r)
L07.7
L.636(2)
1.638(3)
1.633(3)
1.60r(2)
r.607(3)
1.603(s)
1.s83(2)
r.s84(3)
1.614(1)
97.2(2)
99.3(3)
9 9 . 7( 3 )
r09.7(r)
109.6(1)
L09.6(2)
r.637
1.638(2)
1.634(4)
1.636(5)
1.602
1.613(3)
L.623(6)
1,616(7)
r,s8s(s)
1.s84
1.s89(3)
1.591(5)
L.576(7)
r.617(2)
r.614(2)
1.61s
1.619(1)
1.621(3)
1.616(3)
107.4(1)
107.0(2)
106.4(3)
106.6
107.3(1)
1 0 7. 6 ( 3 )
L 0 7. 2 ( 4 )
109.7(1)
r09.7(r)
10e.8(2)
109.9
109.s(1)
110.0(2)
1 0 9 . 7( 3 )
108.3(1)
108.4(1)
108.9(2)
108.s
108.3(1)
1 0 8 . 7( 2 )
1 0 8 . 7( 3 )
1 1 3 . 3( 1 )
r 1 3 . 3( 1 )
rL3.2(2)
113.3
1 1 3 . 6( 1 )
111.8(3)
rLz.5(4)
109.4(1)
r09.4(1)
109.s(1)
109.s
109.4(1)
r 0 9 . 5( 1 )
1 0 9 . 4( 2 )
r.634(2)
1.640(3)
L.644(4)
r.638
L.637(2)
r.641(3)
1.638(s)
r.619(2'
r.614(3)
L.622(5)
r.62Q
1.613(3)
1.607(6)
1.61s(7)
1.s78(2)
1.s74(3)
1.563(5)
1.580
L . 5 7 7( 3 )
1.s7s(6)
r.586(7)
1 . 6 1 7( 1 )
r , 6 L 7( 2 )
1 . 6 1 8( 2 )
r. 619
1 . 6 1 6( 1 )
1.616(2)
1.6re(3)
108.2(1)
108.0(2)
108.0(3)
L07.9
r07.9(2)
1 0 8 . 3( 3 )
1 0 8 . 8( 4 )
111.6(1)
1rr,8(1)
111.8(2)
rr1.7
111,6(1)
1 1 1. 9 ( 2 )
1 1 1 .s ( 3 )
1 0 6 . 8( 1 )
1 0 6 . 5( 1 )
106.6(2)
106.8
1 0 6 . 7( 1 )
L07.0(2)
107.4(3)
1 1 1 .s ( 1 )
1 1 1 . 8( 1 )
1 1 1 .7 ( 1 )
1 1 1 .6
1 1 1 . 6( 1 )
110.5(3)
110.2(s)
1 0 9 . 4( 1 )
1 0 9 . 4( 1 )
1 0 9 . 4( 1 )
109.4
1 0 e . 4( 1 )
r09.4(1)
109.5(2)
1.773(2)
L.779(3)
L.779(4)
L.715
L.779(2)
L.773(4)
L.77r(5)
L.7L6(2)
r.711(3)
1.715(5)
L.7L7
1.715(3)
1.711(6)
L.72r(7)
r.706(2)
1.710(3)
r.707(5)
L.701
1.710(3)
L.726(6)
L.72L(7)
r,742(r)
1.745(1)
L.746(2)
r.744
r.746(L)
r.746(3)
L.746(3)
10s.8(1)
105.3(2)
105.0(3)
105.6
10s.s(1)
1 0 s . 9( 3 )
1 0 s. 3 ( 4 )
107,8(1)
107.8(1)
108.0(2)
107.8
107.7(1)
Log.2(2)
1 0 8 . 1( 3 )
109.9(1)
109.8(1)
LOg.6(2)
109.8
109.8(1)
110.6(2)
110.5(2)
l 1 s , 2( 1 )
l1s.7 (1)
1 1 6 .l ( 1 )
1 1 5 .s
1 1 s .7 ( 1 )
rr-2.9(3)
r14.0(4)
109.4(r)
roe.4(1)
109.4(1)
r09,4
10e.4(1)
r 0 9 . 4( r )
1 0 9 . 4( 1 )
1 76 . 4 ( 2 )
1 7 6 . 3( 3 )
1 76 . 3 ( 4 )
1 76 . 3
176.3(2)
u 3 . 3( 4 )
175.1(6)
L79.s(2)
179.0(3)
L79,5(4>
180.0
179,0(2)
179.0(4)
r78.0(6)
163.s(2)
164.3(3)
164.8(4)
164.0
164.3(2)
162.9(4)
163.6(6)
173.0(1)
173.2(r)
r73.5(2)
r73.4
L73.2(r)
1 7 r . 7( 2 )
L72.2(3)
344
HOCHELLA ET AL,: CRYSTAL CHEMISTRY OF CORDIERITES
Table6. (continued)
Dolnl
I,ftrl.te WelI
Dietance/
Anele
ltrlt1Dllcltv
T21-011-T11
tzl
12l
t2'l
T26-016-T16
T23-013-Tr1
L 2 7. 2 ( L )
1 3 2 . 9( 1 )
r . 2 8 . 2( 1 )
1 2 e . 4( 1 )
Mean
Tlt-or1-M
a2l
l2l
l2I
I2l
I2l
t2l
T11-O13-M
T16-O16-M
T21-O11-M
T23-O13-M
T
24"c
26-OL6-tr
Mean
Ml-O15
-o11'
t2l
t2l
I2l
;3:'
375oc
L 2 7. 2 ( L )
132.8 (1)
1 2 8 7. ( 1 )
r29. 6(r)
775oc
775ocr
r27 .7 (2)
L27.L
L32.6(2)
r32.9
L29.L(2)
L28.9
1 2 9 .8 ( 1 )
L29.6
94.6(2)
94.9
9 4. 5 ( 2 )
94,3
1 3 1 .9 ( 1 )
e 4. 8( 1 )
e 4 . 6( 1 )
9s.r(1)
r37. 6(1)
1 3 5 . 3( 1 )
1 3 1 . 8( 1 )
lr.s.3(r)
115.0(r.)
1r5 . 0(1)
1 1 5 .0
2.rr3<2)
2.LLL<2)
2 . L r 6( 2 )
2.L27(2)
2.119(1)
2 . L 2 4( 4 )
2.L20
2 . L 2 4( 4 )
2.tzL
2 . 1 3 5( 4 )
2 . L 2 8( 2 )
94.9(1)
94.6(1)
95.0(1)
L 3 7. 7 ( L )
r 3 7. 1 ( 1 )
2.L0O(2)
2.Lrs<2)
2. r.08(1)
95.0(2)
9 5. 0
L37.6(2)
1 3 7. 8
L36.2(2)
136.5
r32.O(2)
T3L.7
24"c2
L27.4(r)
132.6(1)
128,3(1)
r29.4(L)
9s.0(1)
e4.5(1)
9 s . 2( 1 )
1 3 7. s ( 1 )
137. 0(r.)
131.9(1)
r l s . 2( 1 )
24"c
Bory
375"C
L 2 8 . 7( 2 )
L 2 8 . 7< 3 )
L33.2(2)
133.4(3)
L29.4(2)
t29.5(3)
130.4(1)
130.5(1)
94.4(2)
e4.L(2)
94.r(2)
e3.e(2)
94.1(z)
94.e(2)
L36,6(2)
136.9(3)
136.0(2)
136.0(3)
131.1(2)
131.2(3)
114.4(1)
114.5(1)
2.Lro(2)
2.Lro(2)
2.Ls3<4)
2.L6L(5'
2.L54(4)
2.L62(5)
2.L32
2.LLg (2)
2.L56(3)
2.L73(5)
2.L24
2.LLz(L)
2 . 1 5 8( 1 )
2 . 1 6 5( 3 )
SitruLated ecpansion by DLS. See text.
Aften heating.
greaterthan 400o,whereas
to expandat temperatures
Lee and Pentecostfind that c continuesto contractat
leastto 1000"C.However,when Lee and Pentecost
annealedtheir hexagonalspecimento produce an
orthorhombic polymorph (with a greaterdegreeof
AllSi order), they discoveredthat the contraction
along c was increasedover that of the hexagonal
polymorph. Becausethe degreeof AllSi orderingin
indialite is probably variable (Meagherand Gibbs,
-
o30
I
z
o
o
z
White Well cordierile (lhis study)
----_
indiolilc {be
-
indiolile {Fl*haiEvona,ond
-
ond Prdecod)
G.igar)
o20
f
il oro
J
E
o*
l!
I
F
o
200
400
600
800
(CCI
TEMPERATURE
Fig. l. Axial expansion([(X, - Xu)/Xrr].100 whereX is a, D or
c) ur. temperaturefor two syntheticindialitesand the White Well
cordierite.The bracketsfor the White Well data aredrawn at * I o.
1977),andbecausethe contractionpropertiesin the c
direction apparently depend on thermal history,
structuralstate.and channelconstituents,we believe
that the differencesin the curvesdeterminedby Fischer et al. and Lee and Pentecostare real and repreon hexagonalpolymorphswith
sent measurements
differentstructuralstates.
Structure
The crystal structureof cordieriteis describedby
Takaneand Takeuchi(1936),Bystrdm(1942),Gibbs
(1966),Cohenet al. (1977),and Meagherand Gibbs
(1977),and consistsof a frameworkof four- and sixmemberedrings of tetrahedra.The six-membered
rings, made up of T, tetrahedra,lie in planesperpendicularto c (Fig. 2). The four-memberedrings,
consistingof alternatingTr and T, tetrahedra,are
linked into chains parallellingc which are further
crosslinkedto form the tetrahedralframework (see
Fig. 3). A neutron site refinementby Cohen et al.
(1977)has shown White Well cordieriteto be completelyordered(tr6 : tzl : tz3:0.0 and trl : tz6=
the probabilityof finding an
1.0wheret,y represents
Al atom in T"y) within the experimentalerror. The M
atoms (M : Mg,Fe) in cordieriteresidewithin the
framework in somewhat flattened octahedra that
sharetwo edgeswith AlOo tetrahedraand one with a
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERITES
345
est temperaturefactor and the greatestrate of increaseto 775oamong cations.
The B"o valuesfor the Dolni Bory cordieriteare
plotted againsttemperaturein Figure4b. Despitethe
varialimited amountof data,the temperature-factor
tion with temperaturefor each cation has the same
generaltrend as that observedfor the White Well
cordierite.Theseobservationsagreewell with findby Cameronet al. (1973)and
ingsfor the pyroxenes
for tremolite by Sueno et al. (1973). Both studies
showthat cationswith higherchargeand lower coordination have smaller temperaturefactors that increasemore slowly with increasingtemperaturethan
cationswith lower chargeand higher coordination.
The six non-equivalentoxygensin both cordierites
are clearlyseparatedinto two groupson the basisof
B"o values.The three distinct O' oxygensare threecoordinated and have smaller temperaturefactors
which increaseat a slowerrate than thoseof the three
independent02 oxygensin the ring which are only
two-coordinated.In general,oxygenswith high coordination aremorerestrictedin movementand display
smallerternperaturefactorsthat increasemoreslowly
with increasingtemperaturethan oxygenswith lower
et al., 1973).
coordination(cl Burnham,1964;Sueno
Fig. 2. Onren (Johnson, 1965) drawing of the cordierite
structure viewed down c (from 0c to 7:c). In ordered cordierite, Trl
and T16 represent Al atoms, while T16, Trl, and Tr3 represent Si
atoms. The M octahedra house Mg and Fe.
SiOn tetrahedron.The large cavities,connectedto
form continuouschannelsparallel to c, house the
water moleculesin hydrous cordierite. The alkali
atoms in alkali-bearingcordieritesresideat the centers of the six-memberedrings of T, tetrahedra
(Meagher,1967).
I sotropic temperaturefaclors
Figure 4a showsthe isotropicequivalenttemperature factors (B"o) for the cations and oxygensin
White Well cordieriteplotted againsttemperature.Si
atoms in the six-memberedring havelower temperature factorsthan Si atomsoccupyingT, tetrahedra
or Al atomsoccupyingT, and T, tetrahedra;furthermore, the B"ovaluesof the tetrahedrally-coordinated
cationsincreaseat the slowestrate relativeto other
B"o values.The temperaturefactors for the tetrahedrally-coordinatedAl atoms increaseslightly faster
than for the Si atoms.The M cationsshowthe high-
Fig. 3. An Ontee stereopairdrawing showing the fourmemberedrings which are linked into chainsparallelingc. Both
symmetricallydistinctchainsare shown(the two overlyingchains
on the left are relatedby a c glide) and have beenhighlightedby
heavy-linedbonds.Note that the octahedron(singleline bonds)
sharesthree edgeswith tetrahedra.In this figure,a is horizontal
and c is vertical.
346
HOCHELLA ET AL.: CRYSTAL CHEM ISTRY OF CORDI ERITES
Table 7. Polyhedralvolumes(A3) us.temperaturefor White Well
and Dolni Bory cordierites
white
o<
Dolnl
WelI
Bory
24'c
a 7 5 "c
7 7 5 "c
24'{
zh"c
a75"c
T1t
2.58
2.57
2.58
2.59
2.61
2.63
Tt6
2.L4
2.L3
2.L5
2.L3
2.16
2.17
Tzl
2.L5
2.L6
2.L5
2.L7
2.18
2.L7
Tz6
2.70
2.72
2.72
2.72
2.73
2.72
T- 2
1 -
2.L6
2.t6
2.L7
2,t6
2.L6
2.r7
11.91
12.06
Polyhedra
@
M
I
tr.79
After
1-1.85 L2.42 L2.55
heati,ng,
may concludethat the orderedconfigurationof Al
and Si in the tetrahedralframeworkof low cordierite
was unaffectedby our heating experiments.On the
('C)
TEMPERATURE
other hand,the octahedralM-O bondsshowa significant increasein lengthwith increasingtemperature.
The Mg-O bonds in White Well cordieriteincrease
0.018A on the averagewhen heated from 24" to
9os
775"C whereasthe Fe-O bonds in the Dolni Bory
cordieriteincreaseby 0.0074 when heatedfrom 24"
to 375'. In the temperaturerange 24" to 375o,the
-t2,./
mean Fe-O bond lengthexpansion[-0.007(l)A] is
,.tt,/t'
less than the mean Mg-O bond length expansion
./
[-0.011(l)A]. This resultagreeswith similarresults
obtainedby Cameronet al. (1973)and is consistent
l<r
'
with the notion that the Fe-O bond is strongerthan
dl
y'"Ft
--17'
the Mg-O bond.
Volumes of the AlOo and SiOotetrahedrashow
little or no changewith heating (seeTable 7). In
contrast,the MgO. octahedrain the White Well cordierite exhibit a volume increaseof 0.27Aswhen
heatedfrom 24" to 775". Similarly, the FeOuoctahedra in the Dolni Bory cordierite show a volume
-'-o
increase
of 0.l3As whenheatedto 375'C.
200
400
(oC)
(b)
TEMPERATURE
The meanthermal expansionof the octahedronin
Fig. 4. (a) Isotropicequivalenttemperaturefactors(B"o)for the the Mg-rich cordierite(12.6 x l0-6oc-1) is signifiWhite Well cordieriteplotted as a function of temperaturefrom
cantlylessthan that observedfor correspondingocta24" to 775"C. (b) Isotropicequivalenttemperaturefactors(B"o) hedrain periclase
(13.9X l0- 'oC-'), forsterite(14.2
for the Dolni Bory cordieriteplottedas a functionoftemperature X l0-6oc-r),and diopside
(14.4X l0-6oc-1)(Hazen
from24" to 375'C.(Thenomenclature
of the atomsfrom a andDis
As
indicated
earlier,the octahePrewitt,
1977).
and
the sameas that in Fig. 2.)
dron in cordierite is isolatedfrom other octahedra
and sharesthree of its edgeswith tetrahedra.Since
Tetrahedral and octahedral bond length expansion
the dimensionsof thesetetrahedrashow little or no
Mean T-O bond lengthsfor individual tetrahedra changewith heating, they act as rigid clamps and
in both the White Well and the Dolni Bory cordier- constrainthe octahedronin its expansionupon heatites do not appearto changesignificantlywith tem- ing. The octahedrain forsteriteand diopsideshare
perature(Table6). Moreover,becausethey are un- edgeswith both tetrahedraand octahedra,whereas
changedafter heating in White Well cordierite,we those in periclaseshareedgesonly with other octa-
-/il(e
'...r1/t
-4vz'<
,Y.ti' ---'_'.rqou
i2'7.:-'
HOCHELLA ET AL..'CRYSTAL CHEMISTRY OF CORDIERITES
347
hedra.Therefore,the mutual expansionof the octahedrain thesestructuresshouldnot be asrestrictedas
in cordierite.If this is true, the meanthermalexpansion of an M-polyhedrondependsupon its environment as well as on the strengthof the M-O bonds.In
fact, when trying to predictthe thermalexpansionof
a crystallinematerial from its structureat 24oC, as
attemptedby Khan (1976),it may be inappropriate
to assigna fixedrate of expansionto an M-O bond
from one structuretype to another.
octahedralthicknessmeasuredalong c is unaffected
by the temperaturechange.This anisotropicexpansion of the octahedronservesto rotate(-0.2") the
rigid six-memberedrings clockwise and counterclockwisein alternatelayersperpendicularto c (Fig.
6). Figure 6 also shows the displacementsaccompanying this rotation of each of the tetrahedralcations in the rings. The twisting of the tetrahedral
frameworkattendingthe rotation is associated
with a
decreasein selectedT-O-M and O-T-O angles,
which resultsin a more efficientpackingof the strucA structural interpretationof the thermalexpansionof ture and a concomitantcontractionof the c cell edge
cordierite
(Fig. 7).
The anisotropicthermal expansionof the unit cell
( DLS) refinement(Meier
A distanceleast-squares
of the White Well cordierite is related to the ani- and Villiger, 1969)of the White Well cordieritestrucsotropicthermalexpansionof its Mg-rich octahedron ture was undertakento learn whetherthe resultsof
and its accompanying
effecton the tetrahedralframe- such a regressionare consistentwith our assertion
work. Changesin the thicknessof the octahedron that the thermalexpansionof the octahedronis the
measuredalonga and b correlatewith changesin the driving force behind the thermal expansionof corlengthsof a and 6, respectively(Fig. 5), whereasthe dierite.The T-O bond lengths,the nearest-neighbor
O...O separations,
and the unit-celledgesusedin
the calculationwereinitializedat the valuesmeasured
,--iat 24o,and the M-O bond lengthswereinitializedat
Fe-cordierile /'l?
t7 24
-{-'
thevaluesmeasured
at775"C.In therefinement,
each
24"C
of the T-O and M-O bondswasassigneda weightof
o{
v
s
17.16
M g- c o r d i e r i l e
/,t
t-;
t 7 . o 8 .z4iq"c
' //.,
3.26
3.30
3.34
3.38
/o(A)
re-coroierit.
Su"'
24cC
o{
a-
76
775"C
3750C /
?o7*
2.44
'
Ms-cordierile
2.48
2.52
/b(A)
Fig. 5. The a and b cell edgesus. the thicknessof the M
octahedronmeasuredalonga,t", and alongb,tr,for theWhiteWell
(Mg) and Dolni Bory (Fe) cordieritesat varioustemperatures.
The
refationshipsbetweena and t" and b and 16are similar for both
cordieritesand seemto be continuousfrom the Mg- to the Fecordierite.The bracketsare drawn at *lo.
Fig. 6. Rotation of the six-membered rings in the White Well
cordierite. The open circles represent the tetrahedral cations in the
ring, the dotted circles the O, oxygens, and the solid circles the
octahedral cations (96 percent Mg). The vectors radiating from the
octahedral cation represent the expanding Mg-O bonds. As
shown, the upper six-membered rings rotate in a clockwise
direction upon heating whereas the lower ones rotate in a
counterclockwise direction. The three independent tetrahedral ring
sites are labeled together with the distance (in A) that thesecations
are displaced about the ring over the temperature range 24o to
775"C.
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CARDIERITES
348
9.37
Pd
ol
5750C
7750C
9.35
106.0
lo8.o
to7.o
tOtl-Tzl-Os16(")
9.37
240C1
rol
3750C
?40C
7750C
9.35
106.0
tos.o
LO16-Tz6-O166(o)
9.37
ol
9.3
>1lrr 7750C
r36.0
r37.0
r38.O
Lr23-Ot3-M(")
Fig. 7. The lengthof the c cell edgeus.oneT-O-M and two OT-O anglesat various temperaturesfor the White Well cordierite.
Theseanglesare oriented such that their changedirectly affectsc.
Their decreaseis apparentlyrelated to the expansionof the
octahedralbonds and slight rotation of the rings.Error bars are
drawn at ilo. (24'C* is after heating.)
l.0, and eachO. . .O separationwasgivena weightof
0.25. More than 40 cyclesof refinementwere calculatedin which the positionalparametersof the atoms
in the asymmetricunit and the cell-edgelengthswere
simultaneouslyvaried.The resultingcell edges(a :
17.143,b = 9.758,c : 9.348A)agreewithin about4
parts in 10,000with those observedat 775"C la :
r7.149(2),b : 9.759(r),c : 9.352(r)Al.In addition,
as the refinedT-O and M-O bond lengthsarewithin
0.001Aof the startingvalues,the resultsof the DIS
refinementindicate that the anisotropicthermal expansion of the unit cell of cordierite is principally
controlledby the thermalexpansionpropertiesof the
octahedron,as concludedaboveon the basisof observedstructuralchangewith increasingtemperature.
As shownin Figure 5, the thicknessof the octahedron in the Dolni Bory cordieritemeasuredalong a
and b is significantlygreaterthan that measuredfor
the White Well cordierite.This greaterthicknessconforms with the larger a and b cell dimensionsof the
Dolni Bory cordierite.Changesin the thicknessof the
octahedronmeasuredalonga and b correlatelinearly
with changesin the cell dimensionsof both Dolni
Bory and White Well cordieriteswith increasingtemperature(Fig. 5). Despitethe largervolumeof the Feoctahedron,the c cell dimensionof the Dolni Bory
cordieriteis 0.054 shorterthan that measuredfor the
White Well cordierite.However.the thicknessof the
Fe-richoctahedronalongc is 0.025Alessthan that of
the Mg-rich octahedron.This differencein octahedral
thicknessalong c preciselyaccountsfor the 0.054
differencein the c cell dimensionbetweenthe two
cordierites(therearetwo octahedraalongeachtranslational repeatin the c direction).Unlike thoseof the
White Well cordierite,both the thicknessof the octahedronand the c cell dimensionof the Dolni Bory
cordierite increasewith rising temperature.AIso,
thereis no evidenceof a rotation of the six-membered
with expansionof the octahedronup
rings associated
to 375oCin the Dolni Bory cordierite.
The efects of heatingon channelconstituents
The loosely-boundchannelconstituentsin cordierite undergo large anisotropic vibrations and positional changesupon heating, as shown in the Ap
mapsat eachtemperatureof refinementfor the White
Well cordierite(Figs.8a-d). The peakascribedto the
alkali and Fe atoms at 0,0,0 is elongatedparallel to
the channelaxis, c, at 375o,while the Ow (oxygen
with thewatermolecule)peak at0,0,l/4is
associated
a singlepeakelongatedfurther alonga than the same
peakat 24'C. AL775"Cin the WhiteWell cordierite,
the Ow peak is absent.It reappearsin the 24o (after
heating)Ap map as a singlepeak, lessthan half the
sizeof the original Ow peak, and is no longer elongatedparallelto a. The absenceofthe peakat 775' is
probably due to high-temperaturefactorsand seemingly completedisorderof watermoleculeswithin the
cavity.The Ow peak alsovanishesin the Dolni Bory
cordieritein the Ap map computedfrom the 375oC
data. On the other hand, the peak ascribedto alkali
ring has enlargedin
ions centeringthe six-membered
White
Well cordierite.
the 775'C Ap map for the
(after
map
for White Well
heating)
Ap
Also, the 24"
(l)
is
more
electrondenthere
shows
that
cordierite
sity at 0,0,0 than in the unheatedsample,(2) less
electrondensityat 0,0,1/4,and (3) an overallsubstantialdrop in the original amount of channelconstituents.It seemsreasonableto suggestthat someof
the channelconstituentshave beendriven out of the
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERITES
iQ
^
zooo
-or2
-o 24
- o t 5 -o 09
016
b
o
o24
"@[o (/{.c
o t2
zo
n
r)
1@{
unc
oo ( - l
c
it
D
f',
349
would be appropriatelylarger (seeTable 7 and Fig.
5). This hypothesisis supportedby our observation
of powderringswith d spacingscorresponding
to the
104,ll0, 024,116,2l4 and300spacings
of hematite
in the precessionphotographsof heatedWhite Well
cordierite.However.if octahedralvacanciesexisted
in the frameworkafter heating,one would expectthe
isotropic temperaturefactorsof the octahedrato be
less after heating than before; this is not the case
(Table4). The observeddifferences
in a and b dimensions of the White Well cordieritebefore and after
heating are probably due to a combination of the
abovefactors.
Orientationof the water moleculesin the While LTell
cordierite
A re-investigationof the water position in the
channels
of the White Well cordierite,as locatedby
U
-o 24
o
o
Cohenet al. (1977} hasled to a newinterpretationof
the orientation of water molecules,from the X-ray
-015 -009 -o03 003 009 0t5
cX
d
and neutron diffractiondata of Cohen (1975).Although attemptsat refining the Ow (oxygenof the
Fig. 8. X-ray Ap maps of the White Well cordierite showing the
peaks asffibed to channel constituents at (a) 24",. (b) 375", (c)
water molecule)position during the structurerefine775", and (d) 24"C (after heating). All sections are the (010) plane
ment were unsuccessful,
X-ray Ap mapsshowOw to
at y : g. Solid contours are positive; dashed contours are negative.
be split into two positions along the x axis at
The zero contour is omitted, and the contour interval is 0.20e-lAs
+.0.021,0,1/4
as shownin Figure 9. Newly calculated
for each map.
neutron Ap maps (seeFig. l0) stronglysuggestthat
the plane of the HrO moleculeis inclined by -29"
structure,while some of the remainingHrO mole- from (100)and that the H-H vectoris l9o from c.
culeshavetaken up positionscenteringthe six-mem- This HrO position is significantlydifferentfrom that
bered rings.
proposedby Farrell and Newham (1967)and Tsang
and Ghose (1972), basedon spectroscopicstudies.
The state of the White Well cordieriteafter heating
The a and D cell edgesof the White Well cordierite
do not return to their originallengthsafter coolingto
24"C (Table2). Observations
suchas theseare usually attributed to a changein structural state with
heating(see,e.g.,Karkhanavalaand Hummel, 1953;
Levien and Papike, 1976).However,this is not the
casefor the White Well cordieritebecauseits completelyorderedstructuredid not disorderat all during data collectionat high temperatures.
A possible
explanationin this caseis that changesin amountand
perhapspositionof channelconstituentswith heating
and cooling causea and b to increase.It is not clear,
though, how thesechangesmight affectthe AloSiuO*
X
framework,if at all (seeLangerand Schreyer,1976;
Fig.
(24'C)
9.
X-ray
Ap
map
showing
the elongatedoxygenpeak
Stout, 1976).Another more plausibleexplanationis
along
the
axis.
(001
x
Section
is
plane
the
at z = l/4. The contour
)
that someof the iron in the framework was usedto
interval is 0.20e-lA8, and the zero contour has been omitted.
form secondaryhematite,and as a resultsomeof the Solid contours
are positive, dashed contours are negative.
octahedrawereleft empty.Octahedralvacancies
take Subtractionof the peakwasmost completewhenelectrondensity
up more spacethan filled octahedra,and a and b wasaddedat i0.027 on x.
- or 2
if
a
lol
Q^
350
HOCHELLA ET AL.: CRYSTAL CHEMISTRY OF CORDIERITES
further supportthe ideathat lesswateris presentthan
reported by Pryce (1973),the amount of hydrogen
neededto diminishthe negativepeaksof the neutron
Ap map shown in Figure l0 is consistentwith
(HrO)o.ru.However, a thermal gravimetric weightlosscurve for the White Well cordierite(C. W. Huggins, 1976,personalcommunication)suggeststhat
the amount of HzO in the formula is correct.
Acknowledgments
for performingthe
Dr. E. P. Meagheris gratefullyacknowledged
DLS calculationsand for reviewingthe manuscript.Dr. P. H.
Ribbe also read the manuscriptand offeredhelpful suggestions.
on
Dr. G. R. Rossmanis thankedfor severalhelpfuldiscussions
oo8 0 r6 o24
032
040
channelconstituentsin cordierites.We thank SharonChiangfor
Z
draftingthe figuresand Marie Phillipsfor her patienttypingof the
Fig. 10.NeutronAp map (24'C) showingthe negativescattering manuscript.This study was supportedby NSF grants EAR74(Gibbs and Ribbe).
035056-40l(Brown) and EAR77-23114
of the hydrogens(zerocontouromitted)in the (100)planeat x =
0.01. Solid contours are negative,dashedcontoursare positive.
References
The Ow peak, that ascribedto the oxygenof the watermolecule,
has beensubtracted.The dimensionsof the two symmetry-related
Bloss, F. D. (in preparation) The Spindle Stage: Principlesand
water moleculesshown are d(Hl-Ow) : 0.994, d(H2-Ow) :
Practice.
:
0
.
0
1
0
,
y:0.025,
l . 0 l A a n dH l - O w - H 2 : 1 0 5 . 1 ' w i t hH l a t x
crystal
Brown, G. E. and C. T. Prewitt(1973)High-temperature
z = 0 . 1 5 0H, 2 a t x : 0 . 0 1 0 , y : 0 . 0 7 8 a n d z : 0 . 3 1 1 a n dO w a t x :
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of
:
0 . 0 2 7y,
0, z: l/4.
-,
S. Suenoand C. T. Prewitt (1973)A new single-crystal
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water
in
et
al.
for
orientation beryl.Goldman
High-temperaturecrystal chemistryof acmite, diopside,hedenstatedthat the White Well cordierite.as well as havand ureyite.Am. Mineral.,58,594bergite,jadeite,spodumene,
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F. K. Rossand G. V. Gibbs (1977)An X-ray and neutron
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67-78.
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380-388.
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(1974)Crystallattice
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HOCHELLA ET AL.' CRYSTAL CHEMISTRY OF CORDIERITES
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Manuscript receiued,December29, 1977;
acceptedfor publicalion,September12, 1978.