URANIUN{ AND THORIUM IN THE ACCESSORY ALLANITE
OF IGNEOUS ROCKS1
Wrrrreu Lre Slrttn,2 MoNa L. Fna'Ncr,3 ,q.Np Ar-BxeNnrn M.
Suonwooo, Ll . S. Geological Suraey, Washington 25, D'C '
ABsrRAcr
u'eight in the rocks studied. The mineral is confined largely to the more siiiceous phanerites.
The uranium content is highest in the ailanite from the granites sampled, ranging from
0.004 to 0.066 per cent, whereas the thorium content is high or low regionally, ranging from
0.35 to 2.33 per cent. Allanite was found to be otherwise of exceptionally uniform composi-
tion.
IwrnooucrroN
Allanite, (RE,*Ca)z(Fe,Al)sSirOrz(OH), may occur as an accessory
mineral in siliceous and intermediate igneous rocks, in limestone contact
skarns, pegmatites, crystalline metamorphic rocks, and as a component
of magmatic iron ores. The mineral is monoclinic and varies in color from
light brown to black. Its hardness ranges from 5 to 6 depending upon
its degree of alteration, and similarly its specific gravity varies from 3.4
to 4.2. Allanite is a member of the epidote group with rare earths sub-
stituting for calcium. Allanite is often found with epidote; some of it is
intergrown with epidote (Hobbs, 1889). The metamictization of allanite
produces an amorphous alteration product, and some allanite from
pegmatite is completely isotropic. The alteration is inferred to be the
result of the destruction of the crystalline structure of allanite by the
radioactive decay of its uranium and thorium.
N{rNBnarocv
Separat'ion method.s
In the granitic rocks that were studied, allanite was found to average
0.1 mm. in diameter. The rocks were pulverized on a roll-type crusher
which liberated the allanite cleanly. The allanite was generally found to
concentrate in the 100- to 200-mesh size fraction. Allanite concentrates
+ Rare earths.1 Publication authorized by the Director, U. S. Geological Survey.2 Present address: Minerals Benefication Div., Battelle Memorial Institute, columbus,
Ohio.3 Present address: Ferro Corp., Technical Service Lab., Cleveland, Ohio'
367
368 w. L. SMITH, M. L. FRANCR AND A. M. SIIERWOOD
with the other accessory minerals in the sink of a methylene iodide sep-aration (sp.g..3.33). It is easily separable from the other heavy mineralsin a Frantz rsodynamic magnetic separator, allanite becoming magneticbetween 0.4 and 0.6 amp. at cross and logitudinal settings of 10o. whenepidote occurs with allanite, the separation becomes more difficult. Theepidote floated and the allanite sank in methylene iodide saturated withiodoform (sp.gr.3.45). Thus a minimum of hand-picking was required. toobtain clean separates of the minerals.
Opti,cal properties
All of the ailanite studied was optically negative. The indices of re-fraction of the allanite were generally higher than those described inliterature. This may be because the minerals generally described are themore metamict varieties from pegmatites. rt is l ikely that the allanitedescribed here is more abundant and more typical of the fresh mineralthan the larger specimens obtained from pegmatites.
The optical data in Table 1 show that the a indices range from 1.690to 1.775, B f rom 1.70 to 7.789, and 7 f rom 1.706 to 1.291 wi th a possib leerror of +0.002. Allanite is reported to have indices as low as n 1.60
Teslr 1. Imrcrs or.RprrlcrroN ol All,qxrre lnou Icxuous Rocrs
q Rl_ o I Birefrin-
____l_-i:_Southern California batholith
Coarse phase
Granite from Rubidoux Mountain, RiversideFine Phase
Granite from Rubidoux Mountain, RiversideWoodson Mountain granodiorite, DescansoWoodson Mountain granodiorite, TemeculaWoodson Mountain granodiorite, RainbowWoodson Mountain granodiorite, ElsinoreGranodiorite, Stonewall formation, CuyamacaMount Hole granodiorite, Mount HoleTonalite, Aguanga
Sierra Nevada batholith
Quartz monzonite, Basin MountainIdaho batholith
Porphyritic granodiorlte, CascadeGranodiorite, StanleyGranodiorite, Atlanta
White Mountains, New HampshireFresh Conway granite, ConwayWeathered Conway granite, ConwayAlbany porphyritic quartz syenite, Passaconway
t . l t J
r . / .1. )1 . 7 4 51 , . 7351 740r .7401 . 7 0 51 .6951 . 7 4 3
1 .750
1 . 7 4 0r . 7 6 r1 .752
1 . 7 2 r1 . 7 2 01 .690
1 . 7 8 9
I . / . ) t ,
1 . 7 6 01 .7501 . 7 5 5I . / . ) . )
1 . 7 r 71 . 7 1 01 . 7 6 0
l . / o o
r . / . ) l
1 . 7 7 61 . 7 6 8
r . 7 3 8| . 7 3 71 . 7 0 0
1 . 7 9 1
l - l J z
1 .7631 . 7 5 3I . I J 9
1 .760| . 7 2 0t . t l +
1 . 7 6 3
1 . 7 7 0
I . / J J
1 7801 . 7 7 1
1 1 A 1
1 . 7 4 01 . 7 0 6
0 .016
0 .0170 .0180 .0180 .019o.o200 .0150 .0190.020
0.020
0 .0150 .0190 .019
0.021o.0200 .016
TJ AND TE IN ACCESSORY ALLANITE 369
among its isotropic varieties. The birefringence' 7-a, is shown to vary
from 0.015 to 0.021 in the specimens studied. The indices of refraction
of allanite from a single rock were found to be variable. The indices
listed are representative. fn the fresh Conway granite the allanite varies
in a index from 1.695 to I.739, and in the Cascade granodiorite the allan-
ite varies in a index from 1.740 to 1.760.There seems to be no clear relationship between the indices of refrac-
tion and the rock type. The Idaho minerals have consistently higher in-
dices, whereas those from New Hampshire have lower indices. AII of the
allanite studied is from rocks of Late Jurassic or Cretaceous age (Larsen,
1948; Chapman, 1955; Hinds, 1934) with the exception of the New
Hampshire samples which are of Mississippian age (Billings, 1945).
Cneursrnv
Chernical analysis
Chemical analyses (Table 2) of allanite from different areas and of
different optical properties were made by Glen Edgington of the Geolog-
ical Survey.
Tltntn2. Cgrurclr AxAtvsns, ru Pnn Cnwr, or Ar,laNrrn lnou ClscAor,Io.lno; Cotwev, Nnw Heursurnnl eNn Rrvrnspr, CeluonxtAl
ConstituentCascade
granodiorite
Granite from
Conway granite Rubidoux Mountain,(fine), Calif.
SiozAlzOsFe:OaCaOMgoMnOHrO (total)
CezOaRe2OB (other)(Total RE incl. ThO)
Total
30. 35/ . 5 0
1 8 . 1 412.907 . 4 30 . 3 82 . 0 0
1 1 . 0 615 .69
(26.7s)99.51
26.057 .54
t7 .o l10 .450 . 8 10. 585 . 6 0
12.451 8 . 6 9
( 3 1 . 1 4 )99. 18
29.758 . 4 2
20.688. S50 . 9 10 . 3 12 . 4 0
1 1 . 3 81 5 . 8 1
(27 .re)98.61
Determined on separate
samoles bv Sherwoodz
Th02U
1 . 20.0036
o .920.0540
0 . 7 60.0400
I Analyses made by methods outlined in Hillebrand and Lundell (1929)2 Uranium determined fluorimetricallv. Thoria determined colorimetrically by thoron
method.
370 w. L. SMITH, M. L. FRANCK AND A. .4[. SHERWOOD
S pectroscopy
Semiquantitative spectrographic analyses of nine allanites from igne-ous rocks are compared in Table 3. The minerals were separated fromrocks of the white Mountains batholith of New Hampshire, the southerncalifornia batholith, the Sierra Nevada batholith, and the rdaho batho-
Aside from the radioactive components, which are discussed separately,most of the variations in composition are within the l imits of precisionof the method. one immediately obvious fact is that each alianite con-tains the same 37 elements, with the exception of the absence of thuliumfrom the Basin I'rountain minerar and the absence of Iutetium from thecascade granodiorite mineral. The variations, which seem to be regional,are the higher content of Nb, Be, and sn in the New Hampshire minerals,and the higher content of the elements Mn, Ti, Ni, and cu in the SierraNevada specimen.
Among the rare earths, in all samples the order of abundance isCe,(La,Nd,Pr), (Sm,Gd), variable traces of Lu, Ho, and Eu. Tm is theleast abundant. Of the cerium earths the order is Ce,(La,Nd,pr), Sm,and Eu. Of the yttrium earths the order is (Gd,Dy), (Er,yb,Lu),(Ho,Tm.)
Rad i oo cl iae com ponen ! s
371U AND TH IN ACCESSORY ALLANITE
+ @F . _ , , x - 3
0 a - r n > r : l u- q d ' " r i I d , - - !
, q < ! a i N l E F z e' 6 6 2 > E a > E z o 6 t 4 r c
d s
a 2- ! 3 v
- ' r F l i i o
. X ^ i ;
4 6
' 1 F P '
, 9 < Z >i t s g i i
- 4 3z c - E zA a - , ; t , \ 6
, e e S i i y r \ S ; ; f 3E o I g F EE , i ; f i i 6 f i
8"1 .=E.q d E ; ? Tc X S
.', i s ; s i !-: E z7, ,v 2 a tr i ia d ,:,8 &
E - 3 . r 88d nE I ;3 i
n 1 f g s* t d ' i 4 z-a 3 2 > i r 8 A ; f i d d F d
O
( J i
Q Z
* a
. 9 oi E
O
> H '
O
F . 8 . :{ : €;g f ,
u q
N . :
d N
. Y B !! 9 F: x
Fr
z|l
z< , y
E I :
6 F.l
& - ;
p . a.h ::F X
H 1
tsz
Ea
|ltr
F
3 XF
d s , ct FZ - F L r o t . = r J > 3 iJ F I _ > r , 1 ;
f , o T" E a ; - i az 2 ,F 'a 3 ? # i r B s # E - 3 a A A
E i . qa r
. 2 2 )< d g E F Z n t -
d r i 7 , > F 14 > r , ? , zFa s s F sE A aE i l o ; a
z z a ? _ o, i F c A o g . ga a i > > E #
, y 8d s i : f i d j i . tE a af i i ia A aA H c, i
- S a 3 . - EA q
2 g d f i df i q 6s c I S ; 1 a 2a ; f i _i l c < e gE A a i I o€
i 5
F
' 5 =
0 .,i4.
E
z
F
F . ,
U E
q . 1 E{ : €;s g
9 r c ;
c * a 6 IE C = G
: o! ? Q 9 9 9
Y Y ; Y Y YP : A = P : e x x =
E t 5o o o do o
E -. 9 0 0 'v : = b H o
; A ; ] ; J\ d c ;
W. L. SMITH, M. L. FRANCR AND A M. SHERII/OOD372
O H O \ 4 O \ N b € ( ) o ON N i : i i i i i N
O \ \ c ) \ O @ S N : \ c ) N \ O. + 4 o | . \ O o O O \ r + O O \€ N N N N N i H H O
- i - l : - i ; , i - i - i - : . {
d ( q o ^
d ; - f id ' d ; J O
a ) a o
O N \ O < r O \ N O d N c Oo O O o O \ O < t \ O a O < t O \ c O4 N N N N : i i O O- i . i ^ , { - i : - : ^ - : . {
O N < i n O \ N N \ O @ DO O \ d O O \ \ O N A O O
\ O Q Q \ O 1 4 O H h N c Oh + = f l o : t r O - ! Q q \\ 9 v ) O O c ) . + 1 - v - e
d o c ; d c j d o i c j o
o
r ! ?
a
a
@
o
o
O c ] O h i N O o o O$ $ o o b N Q N 4 \ O N\ \ \ \ \ \ \ \ : \- H H H i i i H H d
N € \ O i @ O N O O \ Os o N b \ o r o i 4 \ o \ o
\ \ \ \ \ \ \ \ \ " :H i H H H i i i i i
o i i o N b h 4 4 0N N \ O < t 4 O O O < r r -\ \ \ \ \ \ \ \ \ \
i _ H i H
r a d N @ N \ o
; ; d * ' < i ' c ; < , J * < .O i o O O \ N i \ O c ) O < r
N N N i
d o
- o
h
tr
U AND TH IN ACCESSORY ALLANITE
Partly because of their similarity to the rare earths in ionic radius,
uranium and thorium may be incorporated in the structure of allanite.
The radioactive elements accompany the rare earths in many minerals,
for example, in monazite, xenotime, bastnaesite, chevkinite, doverite, and
keilhauite. In the rocks studied allanite has a lesser amount of radioac-
Tnsrn 5. Unexruu Coxrrltr ol Accassonv Arr,ANrto er'ro ol Its Hosr Rocr<sAnalysts: A. M. Sherwood, M. Molloy, and M. Schnepfe
Rock, locationU in allanite U in rocks
(pp-) (PP-)
J / J
GranitesBiotite granite, weathered, Conway, N. H.
Biotite granite, fresh, Conway, N. H.
Leucogranite, fine, Riverside, Calif .
Leucogranite, coarse, Riverside, Calif .
GranodioritesCalifornia
Mount HoleCuyamacaDescansoTemecula
IdahoAtlantaStanleyCascade
Quartz monzonitesCalifornia
Mt. Tom quadrangle
Mt. Goddard quadrangle
Mt. Goddard quadrangle
Big Pine quadrangle
Quartz syenitePassaconway, N. If.
656 12 .0540 13 .0400 3 .7241 4 .1
208 5.91 1 r 1 . 5102 3.7. ) J r . z
45 2 .340 0 .83 6 I . T
9I
7850
7 . 75 . 83 . 82 . O
4 . 6
tive elements captured in its structure than ziron, xenotime' or monazite,
and it generally approximates the radioactivity of sphene, apatite' and
the rare-earth carbonates.Table 4 shows thorium to be high in the New Hampshire and Idaho
minerals and low in the California minerals, regardless of rock type'
Uranium is seen to be high in the allanites from granites from both lo-
calities listed in Table 5.Figures I and 2 show the relation of the calculated total per cent eU
to the birefringence and to the beta index of allanite samples.
A black high-index allanite occurring in late calcite-celestite veins
s74 W. L. SMITH, M. L. FRANCK AND A. M. SHERWOOD
0 . I . 2 . j . 4 . , . 6 . 7Percent eU
Frc. 1. Per cent eU as related to birefringence in allanite from New Hampshire O,Idaho A, and California f.
cutting rare-earth-bearing carbonate rock from Mountain Pass, Cali-fornia (personal communication, H. W. Jafie, 1955) has indices of re-fraction of a 1.79O, P I.8I2, and 7 1.818; a U content of 0.0018 per centand Th in the range of 0.01-0.1 per cent. J. P. Marble (1940) describedisotropic allanite from the Baringer Hil l, Texas, pegmatite withn:1.716,as containing 0.715 per cent Th and 0.033 per cent U. Wells (1934) pre-
0 .1 .2 .1 . l+ .5 .6 ,7Percent eU
Frc. 2. Per cent eU as related to beta index in allanite from New Hamphsire Q,Idaho A, and Califomia O.
q)q .
q)brg..{- k .o)frrl€
x -E
..{
0tq
T] AND TE IN ACCESSORY ALLANITE
sented the analysis of allanite from a Wyoming pegmatite with 1.12
per cent Th and0.017 per cent U. Hutton (1951) describes allanite from
a pegmatite in Yosemite National Park, Calif., as containing 0'95 per
. "nt ThOr,0.015 per cent UOz, and opt ics a 1.769, P l '782,and7l '791'
In a microscopic study of five specimens of black, vitreous allanite from
pegmatites by E. S. Larsen, Jr., of the Geological Survey (Watson, 1917)
u ,ung. from the isotropic to the birefracting forms of the mineral is
resrt 6' unaNruu t;ffiil,xlff:rr"il:T c'rr'rrot*re Rocrs
J / J
RockUranium in epidote
(pp-)
Mount Hole granodiorite
Quartz monzonite, Mt. Goddard quadrangle
Quartz monzonite, Big Pine quadrangle
1310220180
described. The isotropic forms show indices of refraction from ra:1'60
to 1.72. fn a study of the radioactivity of allanite from igneous rocks
Hayase (1954) concluded that thorium was the major radioactive com-
ponent, ranging from 0.5 to 1.6 per cent.The uranium content of rocks varies regionally, and generally in each
region the more siliceous rocks have the higher uranium content. The
relationship of high uranium allanite to high uranium rocks is apparent
from observation (Table 5), but it should be pointed out that only a per
cent or two of the total uranium in the rocks is traceable to allanite.
For comparison three samples of epidote wete analyzed and show com-
paratively higher uranium contents for their rock type and area (table 6).
bpidote is less abundant than allanite in the rocks studied. In all the
rocks epidote was green and allanite was brown or black'
PBrnocnapnv
Allanite was found to be present in the rocks studied in amounts rang-
ing from 0.25 per cent in the granodiorite from Cascade to 0'005 per cent
in the granodiorite from the Stonewall formation. The abundance of
allanite in a rock has no apparent direct relation to the uranium or
thorium content of the rock or mineral and is not related to rock type or
area. Of 81 rocks studied, 31 were found to contain allanite. No allanite
was found in any of 10 siliceous lavas from the San Juan region of Colo-
rado. None was found in five alkalic rocks from sussex county, New
Jersey. No allanite was found in any basalts, norites, gabbros, diorites,
lr nepheline rocks, although geologic literature describes occasional
376 w. L. SMITH, M.L.FRANCK AND A. M. SEERWOOD
occurrences of allanite within such rock types (Iddings and Cross, 1885).Table 7 lists the incidence and abundances of allanite in five suites of
allanite-bearing rocks.
MBr.q.lrrcrrzarroN
Brdgger (1893) in proposing the term metamict for certain rare-earthminerals suggested, " . . . The reason for the amorphous rearrangementof the molecules might perhaps be sought in the lesser stabii ity which so
Tanln 7. INcrloNcn eNn AsuNoeNce or Accrssony Ar-r,alstrE
LocationNumber of Number
of rocks rocks withstudied allanite
Percentage of allanite and rock type
0 0X 0.00X or less
Idaho batholith
Sierra Nevada batholith, Calif.
Southern California batholith 34
Sterling batholith, R I.
White Mountain batholith,N. H.
1,1 6
o 4
4 3
8 5 I granite
2 granodiorites
3 qaartz monzo-nites
2 granodiorites1 granite
1 granodiorite
2 granites1 quartz syeDite
3 granodiorites
7 granodiorites1 quartz syenite1 qtartz mo\zo-
nite
2 granites
complicated a crystal molecule as that of these minerals must have in thepresence of outside influences."* He implied that the rare-earth mineralswere so complex as to prevent them from being permanently combined inthe crystalline state-a definition no longer accepted.
Des Cloizeaux and Damour (1860) noted that isotropic allanite be-came birefringent on heating and showed that both the isotropic andbirefringent allanite existed both anhydrous and hydrated.
Goldschmidt and Thomassen (1924) described the alteration of rare-earth minerals from the crystalline to the glassy state. They concludedthat the important factor is the weak chemical bonding between rareearths and weak acids (sil icic, tantalic). Goldschmidt proposed that formetamictization to take place the crystal lattice must have a weakenough ionic structure to permit decomposition and hydrolysis. Also,he proposed that it is necessary that radiation provide the energy todischarge the ions of the rare-earth eiements. This radioactivity couldbe either from within or from without the crystal. Metamictization would
* Translated by A. Pabst (1952, p. 138).
U AND TE IN ACCESSORV ALLANITE
thus occur as the ionic bond breaks by hydrolysis, and the lattice be-comes isotropic.
Ellsworth (1925) stated that " . . . all minerals containing UOs auto-matically oxidize themselves at a rate depending on the rate of uraniumand thorium decomposition."
Hata (1939) in describing the weathering of allanite reports the alteredportions as being conspicuously high in thoria and conspicuously lowin the rare earths, as compared with the fresh part of the same mineral.As the result of leaching studies, Hata concluded that the alteration isIikely to take place when the ratio of FezOs to AlzOa is less than 1.3 andthe content of thoria is more than 1.5 per cent. The other variables andthe relative proportions of the rare earths were found to have no influenceon the alteration.
Ueda and Korekawa (1954) suggest that the metamictization ofallanite is due to the repeated expansion and quenching of the lattice,resulting in the formation of an aggregate of several phases in both thecrystalline and amorphous state.
Allanite shows various degrees of metamictization and, in the extremecases of some pegmatite specimens, approaches isotropism. The altera-tion of the allanite is suggested to be due to radiation from the uraniumand thorium components which breaks the ionic bonds and permits theentry of water into the lattice of the mineral.
Acrr.towr-BncMENTS
We wish to thank Professor Esper S. Larsen, Jr., of the Geological
Survey who suggested this study and who checked the optical properties
of many of the allanite samples. Thanks are also due to George H. Hay-
field for assistance in mineral separations, and to Glen Edgington,
Marjorie Molloy, and Marian Schnepfe, also of the Geological Survey,for chemical analyses. This work is part of a program conducted by the
U. S. Geological Survey on behalf of the Division of Research of the
u' S' Atomic Energy t"--tttt;:"ERENcES
Brr-r.tucs, M. P. (1945), Mechanics of igneous intrusion in New Hampshite: Arn. Jou,r. Sci'.,243-4, Daly Volume, 43.
Bttiocnn, W. C. (1393), Amofi: Salmonsens store i,ll,ustrereile Konaersationslerikon: l,742-743.
Craru.tN, R. W., Gor:rlnron, Devp, .nxo WAnrNG, C. L., (1955), Age determinations on
some rocks from the Boulder batholith and other batholiths of western Montana:
Geol. S oc. America Bull., 66, 607-609.Drs Cr,orzneux, A., exo Dauoun, A. (1860), Examen des propri6t6s optiques et pyro-
g6n6tiques des mindraux connus sous les noms de gadolinites, allanites, orthites,
euxenite, yrite, yttrotantalite et fergusonite: Ann. chim. phys. (3), 59' 357-379.
377
378 W. L. SMITH. M. L. FRANCK AND A. M. SHERWOOD
Er,r-swonrn, H. V. (1925), Radioactive minerais as geological age indicators: Am. Jow.
Sci., 5th ser., 9, 127-lM.Gornscnurnr, V. M., exo TnouessrN, L. (1924), Geochemische Verteilungsgesetze der
Elemente III: Norshe aidensk.-akad'. Osl'o Arbok 5' 51-109.
Here, S. (1939), The alteration of allanite: Tokyo Inst. Phys. Chem. Res., Sci. Papers,r'o.
923 ,36 ,301 -311 .Hev,tsr, I. (1954), The radioactivity of rocks and minerals studied with nuclear emulsion.
Pt. 2. Thorium content of granitic allanites: Kyoto Imp. Unizt., CoIl. Sci., Mem. ser.
8,21,no.2, t7 l - t83.Hrr.r.ennAro, W. F., nnn Lunonlr., G. E. F. (1929), Applied inorganic analysis: New York,
John Wiley & Sons.Hinds, N. E. A. (1934), The Jurassic age of the last granitoid intrusives in the Klamath
Mountains and Sierra Nevada, California: Am. Jou,r. Sci., 5th ser.,27, 182-192.
I{onns, W. H. (1889), On the paragenesis of allanite and epidote as rock forming minerals:
Am. Jonr. Sci . , 38, 223-228.HurroN, C. O. (1951), Allanite from Yosemite National Park, Tuolumne Co., Calif.:
A m. M i,ner aI., 36, 233148.Inorwcs, J. P., axn Cnoss, W. (1885), On the widespread occurrence of allanite as an ac-
cessory constituent of many rocks: Am. Jour. Sci.,3d ser.,30, 108-111.
MARBTE, J. P. (1940), Allanite from Barringer Hill, Texas: Am. Mi.neral'.,25, p. 168-173.
Pensr, A. (1952), The metamict state: Am. Mineral'.,37r 137-157.
Rawxeue, K., axr Senaue, Tn. G. (19.50), Geochemistry, Univ. Chicago Press.
Uroe, T., AND KoREKAwA, M. (1954), On the metamictization: Kyoto Imp. Unit:., Coll.
Sci., Mem., ser. B, 21, no. 2, !51-162,
WArsoN, T.L. (1917), Weathering of allanite: Geol. Soe. Ameriea Bull'.,28,463-500.
Wnrrs, R. C. (1934), Allanite from Wyoming : Am. Mineral'.,19' 81-82.
Maqwscribt receitd, NotLember 11, 1956
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