American Mineralogist, Volume62, pages 356-36I , 1977
Crystal synthesisof a new olivine,LiScSiOn
JUNIro
The James Franck Institute, The Uniuersity of Chicago
Chicago, I I linois 6063 7
Abstract
LiScSiO.,a new silicateolivine,orthorhombic,Pbnma : 4.8200(4) b -- 10.4392(8) c :
5.9120(4)
A, and the binarysolidsolutionseriesextending
to MgrSiOahavebeensynthesized
both from oxidemixesin air and by high-temperature
solventgrowthusinglithiummolybdovanadateas a solvent.Substitutionof 2 Mgz+ for Lil+ * Sc3+confirmedGoldschmidt's
proposedSc8+-Mg2+
diadochyin ferromagnesian
silicates.
Introduction
(1972) demonstratedthat the metal sitesin the pyroxene
structure readily accommodateSc3+if valencyis
The early investigationsof Eberhard (1908),Goldcompensated
by alkalies.
schmidt and Peters (1931), and Oftedal (1943)
Experimental
studies of (Scs+ + Li+) = Mg'*
showed that scandium is almost always present in
substitution
coupled
in the silicatesnow includessynferromagnesiansilicates (pyroxene, amphibole, olithesis
of
a
new
olivine,
LiScSiOa,and its binary solidvine, and biotite) of igneous rocks. Goldschmidt's
solution
series
extending
to MgrSiOo, forsterite.
dominant theme of diadochy of ScS+with Mgr+ and
Fe2+, based on the similarity of ionic radii (GoldExperimental
schmidt, 1927), has been well supported by a vast
number of modern trace analyses of rocks and
Method of Synthesis I
minerals.
Fine-grain crystallineolivines of the solid-solution
Owing to the lack of direct experimentalevidence
of Mg'?+a Sc3+substitutionand the significantdiffer- series LiScSiOr-MgrSiO4 were synthesizedat subence of ionip radii values betweenSca+(0.81 A) and solidus temperaturesby the solid-statereaction of a
Mg'z+(0.66A; later given by Ahrens (1952),arguments mixture of reagent grade (99.9Vo)lithium carbonate,
have been made against Sc3+= Mgr+ heterovalency scandium oxide, magnesium oxide, and silicic acid.
substitution. However, the effectiveionic radii were The thoroughly-mixed charge was placed in a covrecently revised by Shannon and prewitt (1969) and ered platinum crucible, sintered at 650'C for one
Whittaker and Muntus (1970).This reestablishedthe hour, and then ground in an agate mortar. The temclose similarity of ionic radii of Mg2+ and SQ3+in 6- perature was then raised to 1050'C and maintained
for 24 hours. Alter further grinding, the temperafold condition as follows:
ture was raised to a final firing temperature
Mg2+0.725< Si3+0.745 < Fer+0.780
( l 1 0 0 - 1 2 5 0 ' C , 4 8 h o u r s , s e eT a b l e 2 ) , d e p e n d i n go n
(Shannon and Prewitt, 1969) the solidustemperatureof the composition.Repeated
Mg'z+0.80 ( Sc3+0.83 < Fe'?+0.8?
grinding of the samplewas made at 50"C intervals.A
(Whittaker et al., t970)l single-phasecrystallineolivine was thus obtained; no
peaks belonging to the extraneousphaseswere obCrystal synthesis of Sc-aegirine, NaScSirOo, and
Sc-spodumene, LiScSirO., using high-temperature servedamong X-ray powder diffraction data. A sudsolvents(Ito and Frondel, 1968)and subsequentcrys- den surge of temperature or over-heating of the
chargecauseda loss of LirO, resultingin the appeartal-structure refinement by Hawthorne and Grundy
ance of second phases,notably SczSirO,(d : 3.13,
I Relative differencesbetween
3 . 1 l , a n d 2 . % A ) , a n d a s h i f t o f u n i t - c e l ld i m e n s i o n s
the two sets of ionic radii are due
to the different oxygen bond length used.
of the olivine solid-solutiontoward those of MgrSiOn.
356
357
ITO: CRYSTAL SYNTHESISOF A NEW OLIVINE, LiScSiO'
Theseresultsof the directsynthesisexperimentwithout flux suggesta completeand stablesolid solution
seriesbetweenMgrSiOoand LiScSiOnat subsolidus
temperatures.
Methodof Synthesis2
olivines
datafor theLi-Sc-Mg silicate
Tablel. Synthesis
Run No.
Li2co3
Li2MoO4
0 . 3 5 0s
1 4 .1 5e
0 . 2 0 09
14.1e
5
2 . 0 8g
z.w I
vzos
of single-phase L i 2 s i 0 3
High-temperature
solventsynthesis
1 . 4 39
1 . 2 5s
euhedralcrystalsup to 2 X I X I mm in sizewas scro,
l.4l s
0 . 7 7 5s
solvent Mso
effected,using a lithium vanadomolybdate
0 . 4 5 4s
(Grandin de L'Eprevier, 1972; Ito, 1975). The
t2500c
r2sooc
charges(Table1) wereplacedin a platinumcrucible Sooking temperoture
ing
time
4
dop
4
dop
Sook
a
maximum
of
of 30 ml capacity,heatedslowly to
40c/h
r
o
t
e
4"c/h
C
o
o
l
i
n
g
for
4
to
ensure
complete
days
1250'Cin air, and held
68ooc
58ooC
dissolution.The melt was then cooled at 4oC per Cutoff iemperoture
l
5
m
l
3 0m l
s
i
z
e
C
r
u
c
i
b
l
e
The
excess
more
rapidly.
then
cooled
hour to 650oC,
I
.
3
g
1 . 7s
Y
i
e
l
d
remainhot
water.
and
some
was
in
solvent
dissolved
lmm
m o x .2 m m
Crystol size
ing insolublematterwasrinsedout by hot diluteHCl.
o li v i n e
oliv ine
Products
data are givenin Table l. The
Typicalexperimental
LiScSiO,
Lio.zs5"o.z5Mgo.5osi04
crystalsare colorless,transparent,somewhatelon- Bulk compcitions
gatedalong the c direction(up to 2 mm in length),
with well-developed
{110}{120}prisms,{021}ilOl}
olivinespacegroup of
parturefrom the established
domes,and {010}{001}pinacoids.
Pbnm.ObservedextinctionruleswereOklk : 2n and
Chemicalanalysis
h0lh+l:2nonly.
refinementof the LiScSiOrestabCrystal-structure
Bulk chemical analysis and emission spectrographic analysisof .the olivine were performedto lishedthat Li and Sc are almostperfectlyorderedin
(Steele,Pluth and
determinethe averagecompositionand purity of the M(l) and M(2) sitesrespectively
to the orderedolivine
were Ito-,in preparation),
analogous
by I. M. Steele
analyses
crystals.Electron-probe
detectorand data structureof triphylite,LiFePOn(Fingerand Rapp,
made,usingan energydispersive
reduction proceduredescribedby Reed and Ware 1970).
(1e73).
Unit-cell dimensionsof both end membersand
series
of the solid-solution
compositions
analysisshowed,in addi- intermediate
Emissionspectrographic
powder
diffraction
tion to the major components(Li, Sc, Mg, Si), sol- were refined, using the X-ray
(Mo, V), and a smallamountof Fe; methodwith CuKa' radiationwith Si standard(a =
ventcomponents
impuritiespossiblyderivedfrom reagentsand fur- 5.43062A) using the program of Appleman and
nacewalls(Al, Ca, Na, Ag, Mn, Pb, Ni, Cr, Cu, Ag) Evans(1973)(Table'3).Unit-cellvolumesanda and
linearlywith the correspondor lesslevel.Usingatomic b of the seriesincreased
weredetectedat the 0.00-rr
V
Li
and
Sc,
but c showedslightminima
Fe,
Mo,
and
ing
amounts
of
absorptionspectrometry,Li, Mg,
gravisolidsolution.Slightly
of
binary
by
middle
the
was
determined
near
the
weredetermined,
and SiO,
flux-grownLiScSiOo
for
the
was
ScrO'
larger
cell
dimensions
removal
of
SiOz,
metric analysis.After
LiScSiOo
synthesized
those
of
directly
sumto
The
results
are
compared
EDTA
titration.
determinedby
are probablydue to the entranceof the minor elemarizedin Table2.
Probeanalysisindicatesthat the major portion of ments,mainly V2Ou.
Indexedd-spacingdata for LiScSiOrare givenin
is flux inclusion,but
MoO3foundin thebulk analyses
with
areconsistent
VrOu concentrationcould be as much as 0.1-0.2 Table4. The observedintensities
weightpercent.Dr. Ian M. Steelenoted that VrOu thoseobtainedfrom the singlecrystal.
Specificgravity of the two analyzedcrystalswere
wasfound often in the coreratherthan rim, and some
by floatingseveralcrystalsin Clericisolucleanareascontainedlessthan 0.05 weightpercent. determined
meaand simultaneously
tion at room temperature,
X-ray studies
suringthe specificgravity of the liquid. Measured
X-ray precessionphotographsof data agreewell with the calculatedvaluesgiven in
Single-crystal
SiOnshowedno de- Table 2.
LiScSiOnand LiousTSco
5srMgo.r2.
358
ITO. CRYSTAL SYNTHESIS OF A NEW OLIVINE, LIScSiOT
Table2. Chemicalanalysis
of theflux grownLi-Scolivinecrystals
R u nN o .
Bulk*
Groins**
2
Bulk*
Li2O
r0 . 2 3
N. D,
7.9
scro,
47.10
46.48
Mgo
0.09
0.0
1t.54
si02
4 1. 9
Totol
99.32
88.02
Rim**
Core**
6.2
N. D,
N. D,
36.2
28.4
27.06
29.06
14.0
23.4
24.68
2t.18
41.9
4 1. 9
42.U
41.19
t00.0
99.9
94.38
91.43
Bulk*
0.06
0.0
0.20
N.il
Nil
0.06
0.r0
0.t8
0.06
Nil
3. l9 (meosured)
N. D,
3,21 (meosured)
3.l8 (colculoted)
N. D,
3.20 (colculoied)
FerO,
0.06
0.0
Yzos
0.28
N. A.
MoO,
0,G
Specific
grovity
0.0
0. I r 0.05
Nil
N . D. - Not deiermined; Ni l= Not observed(Deteciion limit 0. 05 wf%); N. A, = Not ovoiloble
* B u l k c h e m i c o lo n o l y s i sb y J . h o .
**Elecfron probe onolysis;onolyzed by l. M. Steele; meonvolue from the onolysisof representotivepoinls.
Melting relationson thejoin Mg"SiOn-LiScSiOo
Sc3+(50ppm and 39 ppm) was found in two hortonoA completeequilibriumstudy of this seriesis be- lite-dunites by Liebenberg (1960). Frykland and
yond the scopeof this note, partly because
a large Fleischer(1963) concluded that the lower concentraportion of the liquidusliesabovethe presenttemper- tion of Sc8+in olivines relative to that in pyroxenes
ature limit of this laboratory.Observationsmade and amphiboles is due to a greater ease in charge
during the synthesis
experiments
indicate,however, compensation in the latter two minerals, both of
which readily accommodate heterovalency subthat LiScSiOndecomposes
to liquid * olivine *
stitutions,
rather than to structural incompatibility o.f
ScrSirOT
on prolongedheatingin platinum above
Sc3+
in
olivine.
This study confirms Frykland and
1150'C in air, but meltsincongruentlyto liquid *
Fleischer's
argument
that if an appropriate valency
Sc2Si2Or*ScrO,
by rapid heating to temperatures
compensation
is
made,
Sc3+ can readily enter the
above 1450'C. This melting trend extends from
olivine
structure.
LiScSiOn
towardthe compositioncontaining
approximately25 molepercentMgrSiOn,but with increasing Other trivalent elements,such as Cr3+, Fe3+,and
thermal stability with higher MgrSiOncomponent. Al3+, have also been incorporated in the synthetic
Rapidmeltingand coolingof this olivineseriesusing forsterite using the same technique. Trivalent oxide
an inductionfurnacesuggests
that a primaryliquidus contents in individually doped synthetic forsterites
field probably extendsfrom MgrSiO. to at least were determinedby the electron microprobe analysis
by I. M. Steeleas follows: Cr-doped forsterite(green)
(Li,Sc)MgSiOo.
Cr2O3 : 1.25 weight percent, Fe-doped forsterite
(yellowish brown) FezO, : 0.39 weight percent(total
On scandiumin naturalolivine
iron), and Al-doped forsterite AlrOg = 0.32 weight
The scandiumconcentration
in olivinesfrom ultra- percent. The maximum limit of this type of submaficand maficrocksin generalis much lowerthan s t i t u t i o n i s n o t k n o w n ; i n e a c h c a s e ,a n e q u i m o l a r
that in pyroxenesand amphiboles(e.g. Borisenko, amount of Li was detected in the bulk analvsis bv
1963). An exceptionallyhigh concentrationof atomic absorption spectrometry.
ITO: CRYSTAL SYNTHESIS OF A NEW OLIVINE, LiScSiOt
359
system
Table3 Unit-celldimensions
of the syntheticolivinesin the binaryLiScSiOr-MgzSiO.
Formulo
Synthesis Condifions
Flux Grourn
LiScSi0O
4 . e 2 UV )
(r) s.e72e(el
r0.444
3ffi.76 (6) 1250{00"c
LiScSi0O
1,8200(4)
(r) 5.e720(5)
r0.43e
300.4e(3) 1250{00.c
Li.
/t/s.
Ol"*
75S".75
UoSi
4.8002(r0) 10.4u(2) 5.e65003)
2e7.et v) 12500c-580"c
****
Li.scs".5g^4s.
gzsio+
4.7867(8)
(r) 5 . % n $ )
r0.367
2%.71(6\ 10000c-5000c
tlS2Si04
1.7544V)
r 0 . 2 00r )
z90..n 6\ 14000c-t000.c
LiScSiO,
4.8158(6)
(r) 5. e686(8)
r0.436
300.04(4) I l00oc,4gh
Li.gos".aoMs.4osi04
Li.6os".
gosi04
ooMn.
4.8040(8)
r0.405(2) 5. e632(l l)
2%.08V) I 150"c,48h
4.7886(6\
r0.366(2) 5.9612(9)
2e5.er (5) I 150.c,48h
1i.405".4,0&1.
zosi04
Li.2os".
zo&t. ooSio+
4.Ve4 (4)
(r) 5. ere (6)
r0.325
2e4.21(4) 1250"C,48h
4.7676(4\
(r) 5.e6e6(4)
r0.265
2 n . E Q ) 1250qc,49h
5. e83e(e)
Direct Synfhesis
I
4 cilrlc diffroctomeferdoto (Steele, Plufh ond llo, in preporotion)
Anolysisfrom RunNo. I in Toble2, flpx grovn.
Anolysisfrom RunNo. 2 in Toble 2, flux g'roivn.
Anolysisfrom RunNo. 3 in Toble 2, flux grown.
In spiteof the aboveresults,noticeable
concentration of Sc3+in naturalolivineshasnot beenreported
exceptin Liebenberg's(1960)dunites.The overall
low concentration
of Sc3+in naturalolivinesmightbe
due in part to their high crystallization
temperature,
wherevolatileelements.
suchas Li. would not enter
concomitantlywith Sc3+into the olivine structure.
This suggestion
is supportedby the low concentration of Li in mafic silicatescrystallizedin an early
(Nockoldsand Alstateof magmaticdifferentiation
len, 1956;Beus,1964).
More carefulanalysisof the dunite describedby
Liebenberg(1960),especially
grains
that of separate
of olivine,usingion probe microanalysis,
might revealmore cluesto an understanding
of Sc geochemistry,and perhapseffectsof Li. An exampleof Sc-Li,
replacingMg-Fe2+,is shownin the chemicalanalysis
reportedby Kukharenkoand Kler (1962)of pyroxenesfrom the alkaligabbrofrom the Kola Peninsula.
Also, a quantitativeanalysisof Sc in the Li-bearing
silicatesfrom variouslocalitiesmay be a worthwhile
geochemical
study.
Conclusion
of a newolivine,LiScSiO.,and the presSynthesis
seriesbetweenMgrSiOoand
enceof a solid-solution
provides
conclusiveevidenceof the direct
LiScSiOr
for
Sc3+substitution Mg2+ in silicates.Chargebalentry of Li+
anceis maintainedby the simultaneous
into Mg2+octahedra.Goldschmidtand Peters'sobservation(1931)of Sc3+= Mg'* diadochyin ferromagnesian
silicates(Whittakerand Muntus, 1970)is
thus confirmed experimentally,although a large
of Sc8+in basicrockshave
numberof traceanalyses
indicatedthis result.Any argumentsmade,basedon
subimprobabilityof the Mg'* e Sc3+isomorphous
stitution in inorganicsystemsshould,therefore,be
refuted.
360
ITO: CRYSTAL
Table 4.
SYNTHESIS
LiScSiO,
OF A NEW OLIVINE,
X - r a y p o w d e r d i f f r a c t i o n f o r s y n t h e t i cl i t h i u m s c a n d i u mo l i v i n e , L i S c S i O o( C u K a ' r a d i a t i o n , S i
s t a n d a r d)
hk
Vlo
d ob's
d colc
020
20
5,23
5.22
ll0
70
4.377
4.W
02l
40
3.%l
3.930
061
l0l
l0
3.751
3.751
r33
hk
Vlo
dok
d colc
123
I
1.735
1.735
24r
20
1.697
1.697
l0
1.670
1.670
20
1.627
1.527
t2
0
l0
3.541
3.539
043
l0
1.583
1.583
ll
I
50
3.526
3.530
301
5
1.551
1.551
t2
I
5
3.045
3.016
3ll
5
1.535
1.535
00
2
60
2.W
2.986
251
5
1.525
1.525
t3
0
20
2.822
2.821
24
2
3
1.523
r.523
t3
I
100
2.551
2.551
21
3
5
1.519
1.519
lt
2
35
2.468
2.467
06
2
40
1.504
r.504
04
I
7
2.391
2.391
00
4
40
1.413
1.1v3
21
0
5
2.U7
2.U8
17
0
I
1.424
1.425
14
0
25
2.296
2.295
33
t
20
1.117
1.417
12
2
35
2.282
2.283
tl
4
l5
2l
I
40
2.186
2. 185
26
0
8
r.4r3
t . 4 rI
r.413
l . 4 tr
22
I
3
2.053
2054
32
2
20
04
2
2
1.965
1.965
34
I
5
20
2
l0
1.875
1.875
24
3
3
l5
I
5
1.825
1.824
l3
4
5
r.366
t.334
r.323
1.320
r.366
r.334
r.323
r.320
ll
3
r0
1.812
r.812
332
8
t.3lI
l.3l I
24
o
20
1.770
1.VO
063
5
1.310
1.310
22
2
5
1.765
1.765
172
l0
1.286
1.286
06
0
5
1.740
1.740
LiScSiO4,O*horhombicPbnm,o--4.8200(4), ts10.4392 (8), c= 5. n2O (l
belween1250ond600qCusingsolvent
ot tempercture
V=300.49(3), syrrthesized
Acknowledgments
T h i s w o r k w a s s u p p o r t e d b y t h e N a t i o n a l S c i e n c eF o u n d a t i o n
g r a n t t o t h e M a t e r i a l s R e s e a r c hL a b o r a t o r y o f T h e U n i v e r s i t y o f
C h i c a g o . I t h a n k D r . I . M . S t e e l ef o r c a r r y i n g o u t e l e c t r o n p r o b e
a n a l y s e sa n d f o r h i s v a l u a b l es u g g e s t i o n sf o r t h e p r e p a r a t i o no f t h e
manuscript, and Professor L. Grossman for his critical reading of
the manuscript.
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ITO' CRYSTAL SyNTHESIS OF A NEW OLIVINE, LiScSiO,
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oxides and fluorides Acta Crystallogr , 82 5, 925-946.
Whittaker, E. J. W and R. Muntus (1970) Ionic radii for use in
geochemistry Geothim Cosmochim Acta, 45, 945-956.
26t5-26t6.
I t o , J ( 1 9 7 5 ) H i g h t e m p e r a t u r es o l v e n t g r o w t h o f o r t h o e n s t a t i t e ,
M g S i O 3 , i n a i r G e o p h y s R e s .L e t t . , 2 , 5 3 3 - 5 3 6 .
361
Manustripl receiued,May I I , 1976, accepted
for publirution, Jull' 27, 1976