561
Conadian Mineralogist
Vol. 30, pp. 561-569(1992)
A PART|AL MOLAR VOLUME FOR B2O3tN HAPLOGRAN|T|C MELT
RUTH KNOCHE, SHARON L. WEBB ANDDONALD B. DINGWELL
Boyerisches
Geoinstitut,UniversitdtBayreuth,PostfachI0 12 51, W-8580Bayreuth,Germany
ABSTRACT
The densitiesand thermal expansivitiesof boron-bearinghaplogranitic glassesand Iiquids have been determined
using a combination of scanning.florimetry and dilatomelry. B2O3reducesthe density of haplogranitic liquids (at
750'C) from 2.295 t 0.006 g cm-r to 2.237 + 0.005 g cm-3 wirh the addition of 8.92 wt. Vo 82o,. Thesedensities
havebeenconvertedinto molar volumesin the binary systemhaplogranite- BrO3.The partial molar volume of 8203,
calculatedfrom a linear fit to the data at 750oC, is ,10.30+ 0.77 cmr mole-r in thesemelts. This value compares
with a molar volume of pure B2O3at this temperatureof M.36 x. 0.22 cm3mole-l (Napolitano et ol. 1965),indicating
a negativeexcessvolume of mixing along the haplogranite- B2O3join. In comparison,at l3moc, the addition ot
Na2O to B2O3reducesthe panial molar volume of B2O3from 46.6 to 32.3 cm3 mole-r ar 45 molegoNa2O (Riebling
1966).The densityresultsreported here, along with the viscosity-reducingeffect of B2O3on granitic melts (Dingwell
et al, 1992),should both significantlyaccelerateprocessesof crystal-melt fractionation and facilitate the evolution of
extremelyfractionatedigneoussystems.
Keywords: B2O3,density, molar volume, haplogranite,silicatemelt.
SoMMAIRE
Nous avonsddtermindla densit6et l'expansivitdthermiquede verreset liquideshaplogranitiquesborifbresau moyen
de calorim6triei balayageet de mesuresdilatom6triques.L'addition de 8.92u/opar poids de B2O1rdduit la densit6
d'un liquide haplogranitique(i ?50'C) de2.295 r 0.006 g c6-3 i 2.237 ! 0.005 g cm-3. Les valeursde densir6ont
6t6 transformdesen volumes molaires dans le systbme"binaire" haplogranite-Bror.
Le vo!'ms tart'.t molaire de
-0.77
B2O3,calculdA partir d'une d€pendancelindaire des donndese 750oC, est 40.30 I
cm3 mole-r dans cesbains
fondus. Cette valeur est inf6rieure au volume molaire du B2O3pur a cette temp€rature, 44,36 t 0.22 cm3 mole-l
(Napoliranoet al. 1965),et ddmontreun excbsndgatif de volumir de m€langedansle systbmehaplogranite-gOq. Par
contre, i l300oc, l'addition de Na2O au B2O3r6duit le volume partiel molaire du B2O3de 46.6 d 32.3 cm3 mole-l
pour une composition contenant 450/ode Na2O (Riebling 1966),Ces r€sultats,ainsi que la r6duction de la viscosit€
desliquides granitiques due au bore (Dingwell et al, 1992),ddmontrent que le processusde fractionnement de cristaux
du liquide devrait en 6tre acc6l6r6,pour ainsi faciliter l'6volution p€trogdndtiquedans cessystCmes
fortement 6volu6s.
(Traduit par la R6daction)
Mots-clds:8203, densit6,volume molaire, haplogranite,bain fondu silicatd.
INTRoDUcTIoN
The role of boron in the petrogenesisof granitic
rocks has received increasing attention in recent
years @ichava\t et al. 1987,London 1987).It has
been observed that some natural granitic and
pegmatiticsystemsconcentrateboron up to I wt.9o
(Cernf 1982,Pichavant& Manning 1984).In some
extreme cases, up to 12 wtt/o BrO, have been
observed(London 1986).A number of experimental investigationsof boron-bearingigneoussystems
have probed chemical effects of BrO, added to
granitic melts. Specifically, the equilibrium phase
assemblagesof the P-T-X regime of boron-rich
petrogenesis(Chorlton & Martin 1978, Pichavant
1981,Benardet al. 1985,London et ol. 1988,1989)
have been determined. In contrast, although the
effect of boron on the physicalpropertiesof melts
is of great industrial importance (e.9., Scholze
1988),little is known about the physicalproperties
of geologicallyrelevant compositions.(There is a
similar paucity of data for the effectsof F, P, H2O,
Ta, Nb, etc,). This situation is particularly
unfortunate for those interested in the physical
evolution of granitic pegmatitesat the magmaticor
hydrothermal stage.We presenta new method for
the direct determination of highly precisedata on
volume and thermal expansivity of haplogranitic
melts at magmatictemperatures.
The densityof silicatemeltsduring rock-forming
processesis a critical factor in the efficiency of
crystal-melt fractionation. Accordingly, the ex-
s62
THE CANADIAN MINERALOGIST
perimentaldeterminationof melt densitieshasbeen
the subject of considerableinvestigation in the
geological sciences (see summary to 1970 by
Bottinga & Weill 1970;also, Mo et al. 1982,Lange
& Carmichael 1987, Dingwell e, a/. 1988). These
investigations have been conducted at low viscositiesin the superliquidusregime,and thus in the
absenceof crystals.Processesoperatingduring the
petrogenesisof granitesand pegmatites,however,
occur at temperaturesthat are much lower than
of melt
thoseemployedin laboratory measurements
densilies using traditional techniques.Extrapolation of experimentallydetermined models of the
density of melts to temperatures of geological
interest is complicated by the relatively large
uncertainty in data on the thermal expansivity of
silicatemelts.
Under appropriate conditions of cooling, crystallization can be avoided, even at subsolidus
temperatures, and glassescan be formed from
silicate melts. The physical properties of these
frozen liquids can then be investigated,just above
the glasstransition, astrue supercooledliquids [i.e.,
in metastable(or local) equilibriuml at temperatures and time-scales that preclude significant
crystallization or liquid-liquid unmixing. Use of
data on these low-temperaturemetastableliquids
in combination with data for superliquidusmelts
provides a wide range in temperatureover which
the physical behavior of liquids can be described.
We have, therefore, begunto study the effect of
boron on the physical properties of haplogranitic
melts in the temperature range of geological
interest,in order to constructbetter modelsfor the
petrogenesisof boron-rich granitesand pegmatites
(Holtz & Dingwell 1991,A116et ol. 1991,Dingwell
et ol. 1992). The present method of determining
densities and thermal expansivities has several
advantagesover previous techniques.The molar
volumes and expansivitiesare more precise than
higher-temperature determinations using the already precise double-bob Archimedean method.
The techniqueis applied at low temperaturesand
high viscositiesinaccessiblewith other methods.
These low-temperature and high-viscosity conditions preclude the loss of volatiles from the melt;
therefore, we can obtain volume information that
is otherwisenonexistent.The coefficient of thermal
expansion is determined directly and does not
incorporate errors of density determinations.
METHoDS
Two boron-bearingsampleswerepreparedfrom
powders of Na2CO3, K2CO3, Al2O3, SiO2 and
HrBO:. The reagentsweredried for 24 hrs at l20oC
before being weighedinto plastic bottles and mixed
b)' agitation for 5-10 minutes. The H3BO3 was
weighedimmediatelyafter openingthe air-tight seal
on the original packing. The starting compositions
were chosento represent5 and l0 wtVo additions
of B2O3to haplogranite HPGS composition. The
HPG8 glassis taken from Holtz et al. (1992)t its
composition is near that of the pseudoternary
minimum at I kbar P(H2O) in the systemSiO2 NaAlSi3Os- KAISi3OE- HrO. The boron-bearing
haplogranitic compositionswere fused directly in
lOd-g batches for 2 hours at 1600'C in 75-cm3
thin-walled platinum crucibles in a MoSi2 box
furnace.The productsof thesefusionshad not fully
reacted and were found to be bubble-rich. To
promote full reaction and homogenizationof the
iamples, the cruciblesweretransferredto a second
MoSi, box furnace equipped with a concentric
cylinder viscometer. The sampleswere heated to
1600'C and stirred f.or -24 hours using a Pt80Rh20
spindle. The melt was inspected periodically by
removing the spindle and checking the adhered
glass. The resulting crystal- and bubble-free
products were cooled slowly in the viscometry
furnace to 4@oC and removed to cool to room
temperature.Cylinders(8 mm diameter)of the glass
samples were cored from the crucibles. These
cylinderswerepreparedwith parallel, polishedends
and stored in a desiccatoruntil use in the dilatometry and calorimetry exPeriments.
Samples of the glasses were analyzed by
solution-basedICP-AES and electron-microprobe
methods.The resultsof the analysesare presented
in Table l. The amounts of B2O3in the glasses
determined by analysis are within error of the
intendedstafting compositions.The proportions of
B2O3 determined by analysis are the basis for
discussionof the results.
A combination of dilatometry and calorimetry
measurementsis used to determine the thermal
expansivityand volume of the supercooledliquids
at temperaturesjust abovethe glasstransition. The
lN Tt{E EFC&Brq BNARY (s%)
TABIJ 1. CLA$I COMPOSTTIONS
BrO,
9O"
tdal
NqO
K.O
A.O,
f,por
4.s3(t
4.60
4.17(6)
4-23
11.89(7) 77.9q21) 12.91
79.10
SPC8B5
,1.66
4.tt
t.rz
4.r0
11.79
12.1x
75.18
78.6t
4.35
s9.9d
1m.mr
sPosBlo
4.23(3)
4.66
3.9550)
4.t5
r1.6(D
t2.n
7r.fr(4)
7E.22
t.v2(9)
99.id
r00.ofi
Co@pcid@
98.48'
lm.00r
t Analysis is al!t@
of l0 bv €t€atM EigoDmbo. CaE@ ClE€bar ir
lo/E dof@ls€d b@e ad 20 3 @nl time
BviLo(h
dlmfuve oodo'uiq
(K).
Sldsdsi
albtb (Na/{l'Sl) ud onhlas
05 tV,-15 !A o bm).
t
elAyr6
5n IcP-AEs beriods dqatbcd
d CR'PG{NRS Na@t.
r
d al. (l9el
by ICP-ABS @rhods ddqlb.d tn Pich!tut
Analys
Narct (amgo ol 2, elth @E h p€mth66).
d dPC-CNRS
I N@lllz€d
b Nap
+ KrO + Af.q
in Plcla@t
+ Slq
-
100
ot al. (1987) pcrfomed
Frfmed
A PARTIAL MOLAR VOLUME FOR B2O3 IN HAPLOGRANITIC MELT
dilatometric and calorimetric measurementswere
performed on glass cylinders (8 mm diameter, 25
mm long) using methods identical to those
describedby Webb et al. (1992). The calorimerry
was performed in continuousscanningmode using
Setaram@
HTC and DSCIll instruments.The hear
flux was measuredfor a heatingrate of 5oC min-l
on glassesthat had been previously cooled from
the relaxedstateat ratesof l, 2, 5 and l0.C min-I.
The calorimeterswere calibrated regularly against
a geometricallyidenticalcylinder of sapphire,using
the heat capacity data of Robie et al. (1978). The
heat capacitiesof glass and melt are estimatedro
havea precisionof t 2.5t/oat lo basedon the four
runs performed on eachsampleand the calibration
of the calorimeters.The dilatometry wasperformed
usinga Netzsch@
TMA 402 quartz-rod dilatometer.
This instrument has been calibrated against sapTABLB 2. MEAST'RED IIEAT CAPACITY AND THBRMAL EXPANSIVTTY
dv
T€e0eE@
cc)
gPct
310
330
A
350
360
370
380
390
400
4r0
420
49
440
450
460
470
4t0
490
5m
510
520
530
5,10
550
560
570
5m
590
600
610
620
630
@
650
@
670
680
690
?m
710
7m
1g
14
750
7&
nO
760
790
m
ilo
sm
830
8,O
850
&o
870
880
890
9m
910
l.ll
t.ll
l.l2
t.t2
t,tz
1.13
t.tz
t.l2
t.l2
l.l3
1.13
!.13
1.13
t.13
1.13
l.t3
1.13
1.14
!.l5
t.l5
l.l5
l.l5
l.ts
t.15
l.r5
l.l5
1.15
1.15
1.16
t.l5
t.t6
t.t6
l.t6
l.t?
r,t1
t.r6
r.r5
lrt6
l.16
1.17
1.19
l.!9
\21
r.u
1.25
Ln
Ln
r.tt
t.2.6
1,2.6
Ln
l.2ti
dT
",
,u.rE-gPotBS
r.gt
t.o7
1.08
l.ot
1.09
1.09
l.l0
1.10
t.l!
t.tz
1.t2
1.12
1.12
l.l3
l.t3
l.t3
r.l4
r.l4
l.!5
t.ls
1.15
l.t6
t.16
t.l1
t,l1
l.lt
l.t8
1.lt
f.19
l.f9
1.19
l.2t
1.20
t.21
t.22
r,24
t.26
1.29
l.3l
t.33
r33
r.33
r.32
r31
r.31
l.3t
1.3t
1.32
t.32
lo' o3
ItFOtBlo
r.gl
l,ct'
1.08
1.09
1.09
1.10
t.lo
l.lt
t.tz
l.l2
l.l3
l.t3
1.13
1.14
t.l4
l.l4
l.t5
t.ls
l.l5
1.16
l.16
1.16
t,l1
t,t1
l.t7
l.l8
l.l9
1.20
1.22
1.23
1.23
r.27
t.29
l.3t
1.33
1.34
t.33
t.32
t.32
t.3t
l.3l
r.3l
l.3t
1.30
1.30
ocr
IIPC8
IIPO8B5
HPG8BIO
19.20
18.90
19.(o
19.20
t9.@
It.,!o
It.z)
1t.{}
1r.60
It.30
18.t0
t8.30
It.70
l1.m
rE30
1t.30
17.90
t1.N
17.90
t7.05
16.06
17.50
t7.05
t7.t0
16.54
t6.74
u.09
16.t0
t7.3t
17.06
fi.u
16.50
18.90
18.92
1t.88
1t.78
lt.3J
t7.9
1t.74
19.00
16.46
t8.6t
18,90
18.07
lt.2t
18.05
1t.25
t8.10
18.35
9.n
lt.l2
1t.05
18.58
18.99
18.93
18.69
lt.3l
16.04
t7,77
832
t7.74
$.42
16.3:t
l6.m
t4.06
17.56
15.12
16.57
16.42
16.&
t6.43
f4.83
16.22
15.,16
t6.26
11.29
t4.a
19.t7
l7.tt
m,6
23.06
26.78
tt.u
n7.12
&.46
4t.6E
6.n
.75
34.29
29.t2
26.18
r2.16
2t.ll
25.29
3t.75
38.69
,t6.90
57.6
U,62
g.u
6t.n
56.21
52.95
4.19
46.97
42.51
41.45
4.22
19.90
19.?8
18.9t
t9.n
It.79
t9.70
t6.52
1t.44
rE.97
t9.41
18.63
t9.62
22.6
t9.43
r7.2t
It.99
lE.7t
22.57
t4.t4
lt.29
t7.75
l7.m
16.58
t9.79
16.59
20.28
20.79
23.@
26.M
2t.83
36.20
47.0r
54.59
63.t4
80.07
73a6
65.4
50.79
51.29
,t6.5r
4t.41
,to.50
34.31
34.53
31.28
23.88
20.22
16.@
rc.n
9.n
563
phire (NBS sheet732), and the molar expansivities
havean accuracyof t 390 at 1o basedon the four
runs performed on eachsampleand the calibration
of the dilatometer. The glasscylindersusedin the
dilatometry are those that were used in the
calorimetry measurements.The scanningrates of
the dilatometry measurements
are identicalto those
of the calorimetry measurements.
The thermal histories of the glassesused in the
calorimetry and dilatometry are the same,in that
the glasseswere cooled from the relaxedstate(1.e.,
from above the glass transition temperatur€) at
rates of l, 2, 5 and 10oC min-I, and the
measurementswere performed at a heatingrate of
5oC min-I. The heat capacity and thermal expansion data for the 5/5 (heating-rate/cooling-rate)
runs are listed in Table 2.
THsony
The derivation of liquid expansivityand volume
data from calorimetric and dilatometric measurements is based on the principles of structural
relaxation in silicate melts. The more general
aspectsof structural relaxationin silicatemelts and
its influence on diffusion, viscosity, and density,
have been discussedpreviously (Dingwell 1990,
Dingwell & Webb 1989, 1990).The rheory of our
procedure for obtaining data on the molar
expansivityof relaxedliquids from a combination
of scanningcalorimetry and dilatometry has been
presented in full by Webb et al. (1992) and is
reviewedhere.
When a silicate glassis heated acrossthe glass
transition region, a time-dependentresponseof its
physical properties occurs. The unrelaxed, "glassy" valuesof volume and enthalpy are replacedby
equilibrium, "liquid" valuesover a finite period of
time. Quantitative models of structural relaxation
in melts have been constructed (Narayanaswamy
1971, Moynihan et al. 1976, Scherer 1984) to
reproduce the details of the time-dependent
responseof melt properties in the glasstransition
interval. The models are completely general,
describingthe responseof property iDas a function
of previous cooling-rate (from the relaxed state)
and experimentalheating-rate(from the unrelaxed
state).
The physicalpropertiesof a silicatemelt depend
upon the ambienttemperatureT and the configuration or structure of the melt. $ilicate glasses
quenched from liquids preserve a configuration
that can be approximated to the equilibrium
structureof the liquid at some fictive temperaiure,
Ts (Tool & Eichlin l93l). To describe,in general,
the relaxed(liquid) or unrelaxed("glassy") properties of a silicate melt, we need to specify the
temp€ratureand the fictive temperatureof the meh.
THE CANADIAN MINERALOGIST
5@
{
\./
aa
[rJ
E.
f,
F
CE
trJ
o-
UJ
F
TU
F-
IIL
temPerature
A - decreasing
temporature
B - increasing
TEMPERATURE
Fig. 1. The cooling (A) and heating(B) paths of a silicatemelt in temperarure-fictive
temperaturespace.
For a liquid, the structure is in equilibrium, and
thus Tr equalsT (Fig. l). Upon cooling of the liquid
into the glasstransition region, the structureof the
melt begins to deviate from equilibrium, i.e., T1
deviates from T. This deviation ultimately results
in a temperature independence of T1 at low
temperaturescorresponding10 the frozen structure
of the glassy state. Upon subsequentreheating
through the glasstransition interval, the value of
Ts once again assumesthat of T, and liquid values
of melt properties are observed.The path of the
value of the property taken during reheating is,
however, different from that observed during
cooling. Owing to the finite rate of equilibration
available for relaxation at the onset of the glass
transition region, there is an overshoot in the
transientvalue of the melt property [i.e., the fictive
temperature of the structure is lower than the
temp€rature,Tr < T (Dingwell & Webb 1990)1.
The temperature derivative of the physical
propertiesof a glassand a liquid [e.9., molar heat
capacity (dH/dl, and molar thermal expansivity
(frl/d!\l can be used to describethe temperature
derivative of the fictive temperature. To do this,
the temperature derivative of any property in the
glasstransition interval (e.g., enthalpy, volume) is
normalized with respectto the temperature derivative of the liquid and "glassy" properties. This
norrnalizedtemperaturederivative, which is equal
to dT/dT, must equal zero for the glass (Ti is
constant) and I for the liquid (Ts equals T). The
temperaturederivativeof the fictive temperatureTr
at a temperatureT' is related to the temperature
dependenceof a macroscopicproperty iD by;
drr I
dr' lr,
t(66/62)- (60/0r)"llr
(Do/6r)e- @&/67)sllrr
rt
..\
where the subscripts e and g are for the liquid
(equilibrium) and the "glassy" values of the
property (Moynihanet al, 1976).It is thus necessary
to devisean algorithm to describethe temperature
dependenceof the fictive temperaturein order to
describethe physical properties of a melt in the
region of the glasstransition.
In the presentstudy, enthalpy H and volume V
take the place of the generalproperty iDin Eqn. l.
Assuming the equivalencein behavior of volume
and enthalpy relaxation for melts with identical
thermal histories(Webb 1992),Eqn. I can then be
rewritten as (Webb et al. 1992,Knoche et ol. 1992)l
dTr I
-if
l,'
c.(T'\ - c""(T")
cfir) - c*(r)
dvg\ _ dvs(T\l
dT
dT
lr.
dv^r)_ gYPl
dT
dT lrr
(2)
In the aboveequation, which relatescoand thermal
expansivity dy/dT, the only unknown parameter
A PARTIAL MOLAR VOLUME FOR B2O3 IN HAPLOGRANITIC MELT
565
1.35
1.30
1.25
i
()
o
!r.zo
?
()
ct
1.15
1.10
1.05
300
400
500
600
700
800
700
800
(OC)
TEMPERATURE
70
T
o
60
I
-9
o
E
50
o
E
o
II
40
F
E'
30
o
E
20
10
300
400
500
600
(OC)
TEMPERATURE
566
THE CANADIAN MINERALOGIST
o
Lu
N
J
E o.s
o
z
300
400
500
600
700
800
('C)
TEMPERATURE
Fig. 2. a. A calorimetric trace of heat capacity for HPG8BS for a heatingrate of 5 K min-l. The glasswas quenched
from the.liquid at a rate of 2 K min-r . b. A dilatometric rrace of expansivityfor HPG8B5 for a heating rate of
5 K min-r. The glasswas quenchedfrom the liquid at a rate of 2 K min-r. c. The normalizedcomparisonof the
dilatometric and calorimetric tracesthrough the glasstransition region.
is the thermal expansivityof the relaxed liquid at thermal histories and heating rates. It is only this
temperatureT' in the glasstransition interval.
internal consistencythat permits the use of the
Owing to the lack of data on relaxed thermal assumptionof the equivalencein behavior of the
expansivity,we recoverthe molar thermal expan- enthalpy and volume relaxation. Small changesin
sivity of the liquid from the dilatometric rrace by composition or fictive temperatureof the melt can
normalizing both the scanning calorimetric and strongly influence relaxation behavior.
dilatometric data:
RESULTS AND DISCUSSIoN
o ' ( r )=
617\ - Ol7)
oe _ os(r)
where the subscripts p and g refer to peak and
"glassy" values, The relaxed value of thermal
expansivity c€unnow be generatedfrom the peak
and extrapolated "glassy" values of thermal
expansivity;the volume and coefficient of volume
thermal expansiona"|/Y(dY /dl)l of the melt can
also be calculated.
We wish to stressthat the above method can
only be applied to calorimetric and dilatometric
data obtained on the same sample using identical
Examples of the heat capacity and expansivity
data are illustrated in Figures 2a and 2b. The
density and data on the coefficient of volume
thermal expansion for the HPG8, HPG8B5 and
HPG8B10 melts are tabulatedin Table 3. The data
on room-temperaturedensity were determinedby
immersion in toluene. B2O3 reduces the roomtemperature(28"C) density of haplogranitic glasses, quenchedfrom the melt at 5oC min-r, from
2.316 t 0.005g cm-3to 2.269 t 0.005g cm-3with
the addition of 8.92 wt.Vo B2O3,or approximately
0.2t/o per wt.9o of BrO.. Thesedensitieshave been
converted into molar volumes based on the
567
A PARTIAL MOLAR VOTUME FOR'82O3 IN HAPLOCRANITIC MELT
therefore estimatedbasedon our results obtained
acrossthe glasstransition for rhyolite, albite and
other similar' compositions. The coefficient of
volume thermal expansionof the liquids increases
4.3t
8.92
n% BrO,
from 29.9 a 3.0 x l0-6oc-r b 49.1 + 3.0 x
bobr wt.
l0-6oCr with the addition of 8.92wt.9o B2O3.
blplostdtt
64.35
64.61
65.00
0ol. ft@ld
Our technique of normalization yields a comBro,
0.0404
0.m5
pleted dilatometric trace acrossthe glasstransition
229to.mt
2.26910.005
d@dry G @i)
2i16i0.005
(Fig. 2c). We can use such a trace to integratethe
(aq
volume changeof the sampleup to a temperature
2.269a0.m5
2.2ttO.W5
am4ty 6 m)
2.295.!O.M
cr50-c)
just abovethe glasstransition. The integrateddata
(o3)
28.47610.055
29.057t0.059
rc1. rclw
28.m9i0.076
on expansivityand the room-temperaturedata on
crsdq
molar volume yield the hig}-temperature molar
ogt)
volumesof the relaxedliquids at temperaturesjust
4,- dv/rydD (xlo{
above the glass transition for each composition.
of 8la
14.611,0
15.9*1.0
16.3*!.0
(7309
(5tdc)
(530'c)
The comparison of these high-temperaturemolar
49.1i3.0
of [qutd
29.913.0
47.013.0
volumes at a singletemperaturerequiresa correc(920'c)
(740'C)
(710'c)
tion using the liquid expansivities.This has been
e shdlrd
dovlad@ ptqqgsrcd tb@8b tho @t@ldi@
€@
calculated for a temperature of 750'C. The
calculatedmolar volumesand densitiesof the three
melts at 750"C are presentedin Table 3.
haplograniteand B2O3components.The coefficient
The molar volumes at 750'C are plotted in
of volume thermal expansion of the glasses Figure 3 as a function of the mole fraction of B2Or.
measuredup to the glasstransition increaseswith The data on molar volume have been regressedto
the addition of B2O3from 14.6 t 1.0 x l0-6oc-r the mole fractions of the haplogranite and B2O,
to 16.3 a 1.0 x l0-6oc-r. The liquid expansivities components(Table 4). Included in Figure 3 is the
for the HPG8B5 and HPG8BI0 have been derived linear regressionto the volume data and a line
using the normalization procedureoutlined above. illustrating the volumes that would result from a
The expansivity of liquid HPG8 was difficult to partial molar volume of B2O3equal to the molar
determine from the dilatometry-calorimetry com- volume of the pure liquid (44.36 cm3 mole-!:
parison owing to the small peak due to the glass Napolitano et ol, 1965).The standarderror of the
transition. The expansivity of liquid HPG8 was linear fit is comparableto our estimatedexperimen3. VOLITME AND COBFFICIBNT (d) OF VOLUMB TIIBRMAL
BXPANSION DATA POR BORON.BBARINO EAPIOGRANITIC MBLTS
TABIJ
n.7
i-
to ficnrid
boric oxl& -a--7"
(Napoftano
aa. rcAe1 .."
29.5
to
o 29.3
E
c'
E 29.1
o
LrJ 2 8 . 9
=
J
o
E,
J
o
28.7
28.5
24.3
haplogranite(HPGts)data
(thisstudy)
2tt.1
27.9
0
0.02
0.04
0.6
0.08
MOLEFRACTIONB2O3
Fig. 3. Volume - compositionrelationshipalong the haplogranite- B2O3join.
0.
568
THE CANADIAN MINERALOGIST
TABLE 4. FIT PARAMETERS FOR MOLAR VOLI'MBS
HAPLOGRANIIts
OF
AND B2O3 MELT AT 750oC
E2%
cn3
decreasedviscosity and increased solubility of
water, should combineto extendthe igneousstage
of boron-rich granitic and pegmatitic systemsto
lower temperaturesand more extreme chemical
compositions.
mole'!
2r.01910.043
40.30 t0.77
28.t23jio.V37
,r4.358i0.041
ACKNoWLEDCEMENTS
4.U*O.73
I frt to volus
of this study uing a linu
rclation of voluo
2 fit to data of this study a8d Brq drta of NapoUteo st aL (f965)
ths stmatard emm in the 6t are shom
Frangois Holtz is thanked for supplying the
chemical data. This work has been partly supported
by the award of a Leibniz Prize to F.A. Seifert.
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