THE AMERICANMINERALOGIST,

VOL. 46, MARCH_APRIL,

1961

NEIGHBORITE, NaNIgF3, A NEW MINERAL FROM THE
GREEN RIVER FORMATION, SOUTH OURAY, UTAH*
E. C. T. Cneo, Howeno T. Evaxs, Jn., BnreN J. Sr<rwNnn
aNn
Cnenr.ns Mrrrow, U. S. Geological,Survey,Woshington, D. C.
ABSTRACT
Neighborite, NaMgF3, occurs in the dolomitic oil shale of the Eocene Green River formation of South Ouray, Uintah County, Utah. It is associated with dolomite and quartz,
and the accessory minerals burbankite, nahcolite, barytocalcite, garrelsite, wurtzite, calcite, and pyrite. The mineral occurs in pink rounded grains or in clear twinned octahedral
crystals 0.1 to 0.5 mm in diameter. It has a vitreous luster, uneven fracture, a hardness of
4.5, and is insoluble in water. The specific gravity is 3.03 (measured) and 3.06 (calculated).
Neighborite is optically anisotropic with very low birefringence and a mean index of refraction 1.364. The crystals are invariably complexly twinned.
X-ray powder patterns show that neighbotite is isostructural with perovskite, CaTiOa.
The pattern was indexed on an orthorhombic unit cell having a prohable space groupPcmn,wrth dimensions o:5.363 A,,t:l .O7OA and c:5.503 A. The expansion of the unit
celi was followed to 954' C. using a heating stage on the diffractometer. At 760" C. the orthorhombic o and c axes coalesce and from 760'to 900'C. the cell is tetragonal or pseudotetragonal with a:3.942 A and c:3.933 A (at 7OO'C.). At 900' +25" C. the unit cell becomes cubic with o:3.955 A. The crystal structure of neighborite is interpreted in termsof the known structure of perovskite.

INrnooucrroN
In an extended study of the mineralogy of the Green River formationof Utah and Wyoming, one of the minerals found in the dolomitic oil
shale proved to be a sodium magnesium fluoride, previousllr undescribed
as a mineral. Its r-ray powder diffraction pattern immediately showedthat it belongs to the perovskite family of crystal structures of formula
type ABX3. The present study substantiatesthe suggestionmade by
Ludekens and Welch (1952) that NaMgF3 is among a group of fluorides
whose structures appear to belong to the various modifrcationsof theperovskite type. The significance of the mineral was further enhanced
when it becameapparent that its struclure is closelyanalogousin detailto that of perovskite itself. In this paper the occurrence,physical properties, crystallography and thermal properties of the new mineral aredescribed.The mineral is named "neighborite" in grateful acknowledgment of the continued friendly interest and helpfulness of Mr. Frank
Neighbor, DistricL Geologist of the Sun Oil Co. at Salt Lake City.
Through X{r. Neighbor's efforts the specimensof South Ouray and SunHavenstrite well cores and cuttings were preserved and made available
to us, thus making possiblethe discovery of not only neighborite but* Publication authorized by the Director, U. S. Geological Survey.
379

380

E. C. T. CHAO,ET AL,

also the new mineral garrelsite with elpidite and burbankite in the Utah
Green River formation.
We wish to expressour thanks to three of our colleagues:Blair Jonesfor his help in the synthesis of neighborite, Nola B. Shefiey for the
spectrographic analysis, and Daniel E. Appleman for the calculated dspacings of neighborite obtained with the Burroughs 220 calculator.
GBorocrc OccunnBNcp
Neighborite was first found as clusters of pink and brown roundedgrains in a dark brown to grayish black dolomitic oil shale of the Green
River formation of South Ouray, Utah. It is associatedwith burbankite,nahcolite, wurtzite, barytocalcite,garrelsite,pyrite, calcite, and quartz.
Cores from the South Ouray well at an unknown depth but somewhere
between 1700 and 2300 feet consist of layers of fine-grained dark brown
to black dolomitic oil shale interbedded with layers of coarsely crystalIine material of barytocalcite and nahcolite. Most of the crystals ofneighborite which occur at the top of the fine-grained shale layer are
rounded to subrounded as shown in Fig. 1. This fine-grained shale layer,
as shown by its r-ray powder pattern, consistsessentially of dolomite andquartz with a minor trace of feldspar. Some rounded neighborite occurs
in discrete grains as inclusions in crystals of barytocalcite in the coarsely
crystalline layers.
Neighborite also occurs as cream-coloredor clear, colorlessoctahedral
crystals (Fig. 2). Such crvstals were obtained from the well cuttings of
the Sun Havenstrite well of Uintah County, Utah, at various depths.
The crystals used in this study occur in cuttings that were collectedfrom a depth of approximately 1930 feet within an interval of 10 feet.
Besidesfragments of oil-bearing dolomitic shale, the cuttings containbarytocalcite and pyrite. The total amount of neighborite obtained isless than thirty milligrams.
The mineral has so far been found only from these two wells in Utah,
which are located lessthan a mile apart in an area about 5 miles SSE ofSouth Ouray, Uintah County, Utah. Cryolite, NaaAIFo, has beenfound in the oil shalesof the Green River formation from Colorado.The
dolomitic oil shale there contains dawsonite, NaAl(COs)(OH)r, andnahcolite.
Pnvsrcar, AND OPTTcALPnoPnnrrBs
Neighborite has a vitreous luster, an uneven fracture, no distinct
cleavage, and a hardness of 4.5. Neighborite is insoluble in water but
slowly soluble in hydrochloric or nitric acid and more rapidly in sulfuric
acid. The specific gravity of neighborite was determined both by the

NEIGHBOMTE, Nau[gF3381

Frc' 1. Typical habit of neighborite crystals: (a) rounded crystals on a thin layerof dolomitic oil shale; (b) ioose clusters of rounded and oblong crystals.

suspensionor sink and float method using methylene iodide-bromoform
mixtures, and with the Berman precisionmicrobalance.under a binocuIar microscope,a 0.3-mm. diameter grain was observedto be suspended
within the. liquid column in a nearly stationary position for five to ten

382

E. C. T. CHAO,ET AL.

minutes. The specific gravity of neighborite determined in this way is
3.02. In another test, a sample of 4.90 mg. of the best hand-pickedoctahedral crystals of neighborite was used for determination of its
specific gravity with the Berman balance. The specific gravity som e a s u r e di s 3 . 0 3 + 0 . 0 3 .
are measurably anisotropic, but show very low
Optically, the cr1'51a15
birefringence about 0.003. The mean index of refraction measured withsodium light at 25" C. is 1.364+0.002. The crystals invariably show

Fro. 2. Clear, single and interpenetrating crystals of neighborite'

complex ill-defined polysynthetic twinning and consequently the opticalcannot be determined completely'
properties
The octahedralcrystals often show, in addition to the complex microscopictwinning, apparent interpenetration twinning' Besidesthe octahedral forms {111} the crystals show small cube faces {100} which
truncate the octahedralfaces. The fact that all of the crystals studied
are multiply twinned was shown by the single crystal r-ray studies'
Cnnlrrcar- CouposrrroN aNo SvNrnpsrs
Becauseof the small amount of clean sample at our disposal, a com-

NEIGHBOMTE, NaMgF3
amounts

ol quartz impurities

383

present in the sample; the presence ofTarr,B 1. Spncrnocnaprrc ANar,vsrsol rnn MrNon ElrurNrs oF Nrrc'sonrre
NaMgF3, lnou Sourn Ounev No. 1 Wrr,l, Urnren Counrv, Ururt

Sr
Fe
Ti
V
Y
Zr

0.5
0.3
o.2
0.06
0.05
0.04
0.03

La
Yb
Cr
Sc
B
Cu
Be

o.02
0.01
0.01
0.01
0.005
0.004
0.0005t Analyst: Nola B. Shefiey.

our method of preparationconsistsof grinding stoichiometricproportionsof NaF and MgF2 in an agate mortar and then sintering the mixture in
air at 750o C. for 5 hours. The fine-grained crystalline aggregate pro_
duced gives an n-ray powder cliffraction pa.ttern identical to that of thenatural mineral neighborite (Table 2).
This compound has also been synthesizedat much lower temperatures by Blair Jones at 300o c. ancl 30,000 bars water pressureand at
450o C. and 30,000bars water pressure.Unfortunately, no single crystals suitable ior r-ray investigation were produced.
The natural environment representedby the dolomitic oil shale inwhich neighborite occurs is that of a low temperature condition. AIthough the small anount of the mineral present seemsgeologicallyinsignificant, the chemical environment w's probably such that magnesium was abundant and aluminum deficient. The fluorine that waspresent thereforecombined with sodium to form neighboriteinstead ofcryolite.
Cnysrar,rocRAl,rry

E. c. T. cEAo, ET AL'

3u

study of the powder Pattern.
a reThe r-ray po*de. diffraction photograph of neighborite shows
d-spacinginmarkable resemblanceto that of perovskite, CaTiOa, both3 the correvalues and intensity of the reflections' As shown in Fig'
not only has
spondenceis so good that there is no doubt that neighborite
the sametle general perovskite type of structure, but also possesses(b) perovskite from
3. X-ray powder diffraction patterns of (a) neighborite anda 57'3 mm' diameter
Magnet Cove, Ariansas. (Patterns made with CuKa radiation, andcamera.)F I fr".

pseudotype of distortions and superstructure of the simple cubic ABXa
amplyishypothesisThis.
itselfu.rit that are characteristic of perovskite
tomeasurements
thermalandconfirmed by the detailed crystallographic
not
suris
correspondenceaSuch
be describei in the following sections.
prising in view oI the close similarity of the radii of the ions involved:
ABXr
A
B

x

CaTiOrNaMgF30.e9A

0 . 9 sA

0.68
1.40

0.65

r.36

NEIGHBORITE,NoMgFs

385

comparison with correspondingdimensionsfor CaTiO3 as given by Kay
and Bailey (1957). The statement by Ludekens and Welch (1952) that
NaMgF3 is tetragonal at room temperature (with a:7.65 and c:7.30kX) is not supported by our work.
The specific gravity of neighborite calculated from the measured unit
cell volume with 4 formula units per cell is 3.06, in good agreement withthe value 3.03+0.03 measuredas describedabove.
Concerning the crystal structure of neighborite, no direct analysis of
it is possibleat this time, and we can only assumethat it is closely similar
to that of perovskite. We rely, therefore, on the penetrating study of thisdifficult problem made by Kay and Bailey (1957). They proved thatthe structure of CaTiOs has orthorhombic symmetry, and that theprobable space groups are Pcmn or Pc2tn. By a detailed analysis of thestructure, they concluded that Pcmn is the correct one, and we may assume that neighborite,the stable low temperature phase, also has thisspace group. The crystal structure is described in a later section.
Hrcu TeiupnRATURESruorBs or, NErcHBoRrrE
Finely ground synthetic neighborite was mounted on the heating stageof a diffractometer. The heating stage was designedto provide a uniform
temperature acrossthe sample surface and temperatures were measured
by means of a platinum-platinum-l0 per cent rhodium thermocouple
mounted at the center of the irradiated surface. The instrument was calibrated against the thermal expansion of silver and the melting point ofsilver. Temperature vvascontrolled by means of an A.C. balancing bridge
circuit in which the platinum heating element acted as one arm of thebridge. Temperature was controlled in this manner to *2o C. for extended periods. Although neighborite is quite stable in air, the heating
chamber was evacuated to reduce convection currents and allow a moresatisfactory temperature control. In operation the heating stage allows
the same resolution obtained with conventional diftractometer mounts
at room temperature.
Preliminary heating runs established that neighborite became cubic
at high temperatures, and that the high temperature cubic cell coincidedwith the pronounced cubic "pseudo cell" present at room temperatures.
The melting point was not determined.
To investigate the transition from the orthorhombic cell at room temperature to cubic cell at high temperature, the lines 002, 200,121,022,
220 and 040 in the orthorhombic cell were accurately measured at aseriesof temperatures. It is most convenient to discuss the changesoccurring in terms of the cubic "pseudo cell," rather than the true orthorhombic cell. Consequently,the parameters a':a/\/2,
and,b':b/12

E. C. T. CHAO, ET AL.

386

Tnsrn 2. X-R.w Powonn D.lr.q lon Nnrcnsonrrn, NaMgFr
Pcmna:5.36t, b:7.67e,c:5.50sA, (utt t.OOt A)
Orthorhombic,
aib:c:0.698i1i0.717
Synthetic2

NaturalliJnnt(A)calc

dn*t(A)meas.
110
101
o20
111
002
l2l
200

0r2
102
201
tt2
130
2ll
022
220
lJl

r22
221
202
040
032
212
r32
231
310
103
222

Intensity(A)d#:'..

4.396
3 .841
3.838
3 .435

3. 8 3
3.44

z.tJl

t

2.715
2.682
2.590
2448
2.411
2.332
2.309
2.300
2.236
2.198
2.129
2.064
2.O4r
1.920
1.919
1.874

2.7r
2.68

4
50
4

2.44
2.41
2.33
2.30

9
4
25

2.23
2.20
2.13
2.06
2.04

18
13
6
6
2

2.44
2.4r
2.33
2.305
2.297
2.232
2.r98
2.128
2.060
2.0N

1. 9 1 8

100

1. 9 1 8

.863
.769

1.862
1.765

7<

3.8s
3.4

J.)

2. 7 1
2.68

r.872
A
a

. /JJ

.74r
.736

1.732

t4l

r.7r7
1.7r7

1.713

301
113
311
123
042
240
321
232

1.700
1.693
I .660I .581|.574
1. 5 6 1
1. 5 5 5
1.536

1.689
r.661
I.J/J

1.5s6
1.530

6
I

7
17
11
o
1l

t6
29
27
30
18
9
7l
7

100
3
A

1.862
1.765
1. 7 5 5

J

r.743
1.733
t .716| .713

3
7
10
6

1.692
r.6&
1.583

8
11

1. 5 6 1
1. 5 5 3

T2
10
28

13
25
1

rntensitYiJ

1 Natural neighborite, taken with film, camera diameter 114.59 mm. CuKa radiation(I-1.5418 A), w=i ntt"t. Lower limit 29 measurable: approximately 6.3'or 14.04 A'
2Synthetic neighborite, using difiractometer, CuKo radiation (I:1'5418
A), Nifilter. Sample contains a trace of NaF, not reported'

NEIGHBORITE,

387

NaMgF3T.c.srn 2 (conti.nued)
Synthetic2

NaturalliJnt"t(A)calc

hkt

142
241
302
213
150
3t2
330

1.510
t .501
r.499
1.485
|.476
|.471
1.465

IJJ

I .4.tO

l.)

.426
.416
.408
.396
.376

I

331
223
322
004
242

1.357

ilnnt
(A)meas,Intensity

ilnxt(A)meas.

1.499

1.497

1.473

r.47s

1.434

1.435

1. 4 1 5
1.404
1.371
1. 3 5 6
1.3,10
1.327
1.300
1.282
r.268
1.256
r.234
1.220
1.213

1
I
J
IJ

n

2
4b
3b
1b
1b
a
a
A

Intensity

1.4r5
1.406
|.373
1. 3 5 5
1.340
1.329
1.298
1.284
1.233
t.222
r.212

15
3
z

4

I
1
5

Tasrn 3. Unrr Cnr,r,DrurNsrons or Svrrnrrrc Nrrcgnourn nxo Prnovsrrrn
Data for CaTiOsfrom Kay and Bailey (1957)
NaMgF3 (18" C.)aDca : b :ca' : a/ t/2

b':b/2c':c/J2
a' ib'ic'V'

5 . 3 6 3 + 0 . 0 0A1
7.676+0.W|
5.503+0.001
O . 6 9 8: l7: O. 71 6 9
s . 7 e 2A
3 .838
3. 8 9 1
0.9880:1:1.0138
56.63As

CaTiOs (Temp. not stated)

s.3670+0.00014
7.6438+0.0001+ 0.0001
5 .4439.7t2l90 .70213:l:O
3. 7 9 s A
1
3.82193.8494
0.99298:1:1.00719
5 5 . $ 4A 3

388

E, C, T. CHAO,ET AL,(where a, b, and c are the unit cell edgesof the orthorhombic
c' :c/J2cell) were calculatedfrom the measurementsand these are presentedin
Table 4, and illustrated in Fig. 4.
With rising temperature neighborite remains clearly orthorhombic,
although the at and c' Iengths become progressively closer together.
At 760" C., and a'and c'lengths becomeidentical, an efiect which canbest be observed by the coalescenceof the 220 and 022 lines. Above
7 6 0 oC . , a ' a n d c ' r e m a i n i d e n t i c a l b u t 6 ' i s s t i l l m e a s u r a b l y l e s st h a n a t .
The cell is now tetragonal or pseudo-tetragonal.At 760" C., all reflections with orthorhombic indices A odd, and those with fr even and h*l'
odd disappear,indicating that the tetragonal cell is congruent with theformer "pseudo cell." The unit cell-edgesof the new tetragonal cell at
t h i s t e m p e r a t u r ea r e a : b : 3 . 9 4 2 L a n d c ( : b ' ) : 3 . 9 3 3 A . T h e t r a n s formation matrix from the orthorhombic cell to the tetragonal cell isoroo 2oo 3oo ooo,rfiBo..E)

7oo 8oo eoo tooo

Frc. 4. Variation in cell constants of neighborite with temperature, showing
transition points at 760" C. and 900' C.

NEIGHBORITE,

389

NaMgFgT,q.nr,r 4. DrueNsroNs ol rnn Cusrc Psrunocar-r- lN Nlrcnsonttr

Drrlrntnr

At

Tnupnn.a.ruxos

a'A

b,A

c'A

i/V L

633
700
724
749

3.792
3.812
3.832
3 .848
3 .8703.886
3 .9083.923
3.931
3 .938

3.838
3.848
3.860
3.872
3. 8 8 8
3 .898
3. 9 1 0
3.920
3.926
3 .930

3.891
3.894
3.901
3 .908
3.9r7
3.924
3.934
3 937
3.938
3.94r

3.842
3.853
3 .8643.876
3.892
3 .903
3.9r7
3.927
3.932
3.936

Tetragonal
800
837

3 .945
3.948

3 .938
3.9M

3.945
3 .948

3.943
3.947

Cubic
900
954

3 955
3.960

3.955
3.960

3.955
3.960

3.955
3.960

Temp.'C

Orthorhombic
18
110
220
JJJ

457
.)J /

Intheorthorhombicphase,6:t/2'a',b:zbt,c:\/2'c';inthetetragonalphase,a:a'thepseudocell':c';c:b';inthecubicphase,o-o:b':c'.1,1t:a'b'c'rthevolumeof-+/0+0. Figure 5 shows the diffractometer records of the+O+/+,0,
cubic phaseat 900" C. and the orthorhombic phaseat 18o C. From 760o
to 900oC. neighboriteremainstetragonal,but the axesgradually become
closerin length. Above 900' C. the three axesbecomeidentical and thecell is cubic. Designation of the transition temperature as 900" C. islargely based on the projection of the a' andb' axial lengths versus temperature plots. Since the curves convergeat a small angle the intersection
point necessarily has a large uncertainty and the tetragonal->cubictransition temperatureshould be consideredas 900o* 25" C.
The progressivetransitions from orthorhombic to tetragonal to cubic
can best be demonstratedby observingthe 200,002 and 121 reflections.
At 760' C. the 200 and 002 lines becomecoincident but are still clearly
resolvablefrom the l2l. Lt 900' C. all three lines become coincident
reflecting the cubic cell. The transitions are rapidly reversible and to ourknowledgethe tetragonal and cubic forms cannot be quenchedto room
temperature.
A plot of the cube root of the volume of the "pseudo cell" against
temperature (Fig. a) has a small inflexion at 76O" C. and another at approximately 900b C. Since no abrupt break in the curve is observed both

3e0

I':. C, T, CHAO, ET AL.

Frc. 5. X-ray diffractometer traces of neighborite at (A) 18' C. and (B) 900" C., CuKa
radiation, demonstrating disappearance of superlattice lines in the higher temperatureform.

the orthorhombic--+tetragonal and tetragonal-+cubic transitions are atleast secondorder and possibly higher order, transitions.
Cnysrer CuBursrny
Neighborite belongs to the simple class of crystal structures with general formula ABXs, commonly known as the "perovskite family" (Wells,
1950, Megaw,1957). The ideal structure is cubic with a unit cell about
3.8 to 4.0 A on edge,containing one formula unit. The structure consistsof A and X atoms in cubic closestpacking with B atoms insertedin octa-

NEIGHBORITE, NaMgF3

391

zFrc. 6. Schematic views of the probable crystal structure of neighborite, after the
structure described for perovskite by Kay and Bailey (1957). Na atoms are represented bylarge shaded spheres, Mg atoms by small circles and MgF6 groups by shaded octahedra.
Full lines outline the orthorhombic unit cell and dashed lines show the cubic pseudocell.
The Na atoms lie on mirror planes normal to the y axis, seen on edge in the view at right.

hedral cavities. If the A atom is significantly smaller or larger than X,
the simple structure is generally distorted to a lower symmetry. Thus, inperovskite itself, for which calcium is a little more than half the size ofoxygen, the symmetry becomes orthorhombic and a superstructure isformed with a unit cell four times the sizeof the ideal cell. Such distorted
structures often transform to the ideal structure type at some higher
temperature, and for perovskite, there is evidence that such a transition
doesoccur at about 1260oC. (Megaw, 1957, p.91). In the heating experiments on synthetic neighborite,this transition was positively identified
at 760oC.
On the basis of their single crystal intensity data alone, Kay and
Ilailey (1957) could not distinguish between two possiblestructures for
CaTiOs. One of these two resulted in highly distorted octahedra with
L'i-O distancesranging between 1.78 and 2.08 A. The other (shown in
Fig. 6) has fairly regular octahedra (Ti-O distancesall 1.93 A), the distortion of the high temperaturecubic structure being manifestedonly inthe tilting of the polyhedra. Kay and Bailey accepted the latter mainly
on grounds of parsimony, even though other structures such as BaTiO:
and PbTiO; (Nlegaw, 1947, p. 108) show large distortions in the TiOooctahedra. The cause of the distortion in the perovskite structure has
been commonly attributed to the relatively small size of the calcium

392

E. C. T. CHAO,ET AL.

atom. Kay and Bailey's proposedstructure effectively reducesthe coordination for calcium ftom 12 (for the undistorted high temperatureform) to 8 (8 Ca-O clistanceso12.4_2.5A; the other 4 become3.0-3.1 A).
Since it is well known that titanium can sufier considerabledistortionof its boncling with oxygen, presumably becauseof the largely covalentcharacter of the bonds and the influence of the available 3d' orbitals in
forming hybrids in the formation of these bonds, the crystal chemicalarguments for the CaTiOa structure presented above do not rest on a
firm theoretical basis. The situation is different for neighborite, however.
Here the bonding is largely ionic, and no d-hybridization is possible.
Therefore, there is no reason to expect the MgF6 octahedra to departfrom regularity any more than is necessary,and the tilted regular octahedron structure can be accepted with much more assurance.Fortunately, the closeanalogy betweenthe structuresof NaMgF3 and CaTiO3strengthens the arguments set forth by Kay and Bailey for this structure
for the latter.
The appearanceof the tetragonal phase between the lorv temperatureorthorhombic and high temperature cubic forms does not have any
obvious explanation. The tetragonal cell consistsof a slight distortion of
the cubic cell(c/a:0.9977 at 760'C.), similar to that of BaTiO3, which
is cubic above and tetragonal below 120o C', the latter phase having
c/a:1.0O9 (Megaw, 1957). The tetragonal distortion in BaTiOa is certainly due to a pronounced polarization of one of the Ti-O bonds (Evans,1953) of a kind which has frequently been found in transition metal oxideand fluoride structures. Such a polarization seemsimplausible in an ionicmagnesium fluoride structure, and we believe that the explanation moreprobably lies in some special type of thermal vibration. As the temperature of the orthorhombic form is increased, the degree of tilting of theoctahedrain the o-c plane (Fig. 6, top view) must becomeless and lessuntil at the transition temperature 760", the pattern becomes quite
square. If the Mg-F-Mg links which tie one Iayer normal to the newtetragonal axis to the one above or below is still bent as it was in theorthorhombic phase, the tetragonal c axis (i the orthorhombic D axis)
would be slightly shortened with respect to the a axis, as is observed.
This shortening may be contrasted with the slight lengthening which
results from bond polarization as in BaTiOs and PbTiO3. The bending of
the bond would be randomly oriented with respect to the tetragonal caxis, correspondingto a libration of the fluorine atom about the Mg-Mg
axis. The reason why such libration might be emphasizedonly on alternate fluorine layers in the structure is not revealed by our speculation.

NEIGHBORITE, NaMgFt

393

RslBRENcns
Evrws, H. T., Jn. (1953) A4 X-ray difiraction study of barium titanate: Teehnical Report
No. 58, Laboratory Jor. Insulat'ion Research,M .L7., Ca"mbridge, Mass,
Kev, H. F., rNo Berltv, P. C. (1957) Structure and properties of CaTiOs: Acta Cryst. lO,
219-226.
LuorrnNs., W. L. W., axo Wnrcn, A. J. E. (1952) Reactions between metal oxides andfluorides:somenewdouble-fluoridestructuresoftype,4BF3l AcIaCryst.5r847.
Mrcew, H. D. (1957) Ferroelectricity in Crystals: Methuen and Co. Ltd., London, 236 p.
Wrr.ts, A. F. (1950) Structural inorganic chemistry, 2nd ed: The Clarendon Press, Odord.
M anuscript r ecei,t:ed
J une I 1, 1960.