AmericanMineralogist, Volume60, pages 285-291,1975
Nordstrandite,Al(OH)r, from the GreenRiver Formationin
Rio Blanco County, Colorado'
Csnnlts MIlroN
The GeorgeWashingtonUniuersity,Washington,D,C,,
and U.S. GeologicalSuruey, Washington,D.C.
Eoweno J. Dwonxx, ANo Ronnnr B. FtNxnr-uerl
U.S. GeologicalSuruey,Washington,D.C.
Abstract
Nordstrandite, AI(OH)', occurs as thin fissure fillings in dolomitic marlstones and oil shale of the
Green River Formation in northwestern Colorado. Here. and in New South Wales, Australia, it is
found with dawsonite, NaAlCOr(OH)2, but in the sevenother known occurrencesit is found with gibbsite
in bauxitized igneous rock or karst limestone residues.The occurrence may explain the "surplus AlrOs"
observed in chemical analysesof dawsonite-bearing oil shale in Colorado; thermal study suggeststhat this
is oresent as an aluminum hvdroxide.
Hathaway and Schlanger(1965) describedthe
nordstranditeas depositsin voids in basal
Guam
Van Nordstrand,Hettinger,and Keith (1956)synlimestone
overlying fossil soils formed in basaltic
thesizeda new form of Al(OH)s which they termed
rocks
and
tuffs. Ground water, leachingthesesoils,
"bayerite II"; Papee,Tertian, and Biais (1958)esin the limestone,at pH 8.5
nordstrandite
deposited
tablished its difference from bayerite and gibb(Wall et al, 1962),
in
Sarawak
or
9.
Similarly,
site-two otherpolymorphsof Al(OH)3-and named
near bauxitized
in
limestone
occurs
nordstrandite
was
it nordstrandite.
A few yearslater,nordstrandite
(1967-68)
rocks.
Maric
igneous
intermediate-to-basic
discovered
in Guam (Hathawayand Schlanger,1962,
powder
for
nordstrandite
gave
data
and
described
1965),in Sarawak(Wall, Wolfenden,Beard, and
gibbsite and bayeritefrom Jurassic
Deans, 1962), in Montenegro (Tertian, 1966), in associatedwith
terra rossain the Dinaric Alps of
karst
limestone
and Peter,1967),in Croatia
Hungary(Naray-Szabo
referredto a similar occurrencein
He
also
Croatia.
(Maric, 1967-68),in New South Wales,Australia
(Tertian,
1966).In Hungary, NarayMontenegro
(Goldberryand Loughnan,1970),in Jamaica(Davis
of
(1967)examinedsix occurrences
and
Peter
Szabo
and Hill, 1973),and now in Colorado.
gibbsite(or
one
containing
all
but
nordstrandite,
In Coloradoand New SouthWalesnordstrandite
Wales,Australia
with dawsonite,NaAlCOr(OH)2.In all bayerite)as well. In New South
is associated
rims
1970),
nordstrandite
(Goldberry
Loughnan,
and
the associationis with
other known occurrences,
Hill
Davis
and
In
Jamaica,
nodules.
dawsonite
gibbsitein bauxite,or in residualterra rossasoils.
gibbsitein fer(1973)
with
nordstrandite
observed
Nordstranditehasbeenfoundin two coresamples
(Fig. l, a and b) of dolomiticmarlstone("oil shale") ruginouslimestonesoils(terra rossa).
Therefore,threedistincttypesof nordstranditeocfrom the Green River Formation, in the Sinclair
(l) most commonly,as
CrossV No. I well,Sec.21,T. I S., R. 98 W., Rio currencehavebeenreported:
product in bauxitic soils derivedfrom
Basinof northwest- a weathering
BlancoCounty,in the Piceance
in Europe,Guam,Sarawak,and Jamaica;
ern Colorado, at depths of 1087 feet and 1154.4 limestone,
(2) as a vein or fissure-fillingmineralin dolomitic oil
feet. This is the first discoveryof the mineral in
shale in the Green River Formation, northwestern
the United States.
Colorado;(3) as alterationproductsof dawsonite
t Publication authorized by the Director, U.S. Geological
which may have replacedglauberitein New South
Wales.Australia.
Survey.
ReportedOccurrences
286
MILTON, DWORNIK. AND FINKELMAN
from Guam shown by Hathaway and Schlanger
(1965,their Fig. 2).
have a silky luster,and in the core
The aggregates
specimenfrom 1087feet they grade into extremely
thin bluish films, individualcrystalsonly beingdis(Fig.
cernibleunderthe scanning
electronmicroscope
2). Individual crystals are too small for optical
measurements,
but aggregates
havea mean index of
refractionnear 1.570.This is lower than the indices
reportedfor nordstrandite
from Guam (a, B : 1.580,
:
(c : 1.580,0: 1.581,
1.596)
and
from
Sarawak
r
=
I
is
closer
to
those
from Croatia(q, I =
.613),
but
7
(all + 0.005).
1.565-l.570,7 : 1.585-1.590)
X-Ray Dffiaction Data
Table I gives X-ray powder data for various
nordstrandites
datafor gibbsiteand
and comparative
bayerite,the other two Al(OH)a polymorphs.The
most completenordstranditepattern is that of the
synthetic(Bosmans,1970),but his indexingand unit
cell constantsare here omitted. Bosmans'definitive
work on the crystallographyof nordstranditesupersedes
the earlierstudiesby Van Nordstrander c/
(1956),Papeeet al (1958),and Lippens(1961),which
(1962,1965)
werecitedby Hathawayand Schlanger
in verification of their discoveryof the mineral in
Guam. Similarly,Bosmans'study reviewsand ex-
Ftc. l. Core samples from the Sinclair Cross V No. I well, Rio
Blanco County, Colorado, showing nordstrandite as a whitish
coating. r. Core from a depth of 1087 ft; b. from 1154.4 ft.
Because
manyof its properties,
in particulartheXray diffraction pattern, are similar to thoseof gibbsite,nordstrandite
is probablyan unrecognized
constituentin many other similar bauxite-terrarossaoccurrences.
Nordstranditein Colorado
Appearanceand Optical Properties
The Colorado nordstranditeoccurs as very thin
layersofwhite platy or fibrousaggregates
in fractures
at high anglesto beddingin fine-graineddolomitic
siltstonesand oil shale(Fig. l). Under high magnification (Fig. 2), these deposits resemblethose
Ftc. 2. Scanning electron photomicrograph of a radiating cluster
of nordstrandite. Sample from the Sinclair Cross V No. I well, Rio
B l a n c o C o u n t y , C o l o r a d o ( 1 1 5 4 . 4f t d e p t h ) . ( x 5 6 0 ) .
NORDSTRANDITE FROM THE GREEN RIVER FORMATION
287
378and 386are
tendsthat of Saalfeldand Mehrotra(1966,Xnpp l8- in Table3. The Si and Ca in analyses
3l).
895,the
matrix.
Sample
to
admixed
due
undoubtedly
Table 2 gives three patterns of Colorado nord- smallestand purestsample,showsAl asvirtuallythe
stranditeto indicate the range of variability ob- only constituent.
served. Patterns 2a and 2b, from relatively large
With respectto the 3 percentCa in one sample,
and thereforeprobably impure samples,are never- detrital calcicplagioclaseis abundantin thesecores
theless in fair agreement.The third, 2c (consid- as well as authigenicalbite (and K-feldspar).
ered the best and previouslyshown in Table l),
The nordstranditefrom New South Wales,Auswas obtainedby long exposure(20 hours)of a very tralia, also contained7.9 percentSiOr, mostly as
small,carefullyselected,probablyquite pure sample. quartz, and was intergrown with calcite and dawThe powder patterns of the three A(OH)g sonite;in the publishedpowderpattern,quartzlines
polymorphs-nordstrandite,
gibbsite,and bayerite- were omitted. The agreementwith other published
all show a general similarity, so that in some nordstranditepatterns,althoughnot perfect,is accasesconfusionis possible,more so betweennord- ceptable.
stranditeand gibbsite.Bosmans(1966)showsthis
graphically, and others have commented to the ThermalBehauior
sameeffect.The strongestline of (synthetic)gibbsite
The thermalbehaviorof nordstranditeis of paris 4.82 A lXrrn 12-460);and the strongestlines of
(Table ticular interestsincethis wasthe first intimation that
Guam, Sarawak,and Jamaicanordstrandites
l) are respectively
4.789,4.790,and 4.80, as com- Al(OH)a might be presentwith dawsonitein the
pared to 4.775,4.80, and 4.791-mean 4.789-for Colorado Green River Formation.Thus, from therA second"standard"gibb- mal analysis of the dawsonite-bearingColorado
Coloradonordstrandite.
site pattern is given in Xnpn 7-324, where the Green River oil shale,Smith and Johnson(1967)
strongestline is 4.85 (gibbsitefrom Massachusetts). reportedindicationsof an unknownmineralwith enM. C. Van Oosterwyck(written communication, dothermsat 330"-350oand at about 500'C. It was
1974) noted that four small peaks appear to be rapidlysolublein l0 percentHCI or strongbase,condiagnosticof nordstranditeus gibbsiteand bayerite, tainedaluminumbut no sodium,and is "not detectit is
citing those describedby Van Nordstrand el a/ able in oil shaleby X-ray diffraction,"because
weak
very
or
has
amorphous,
X-ray
"amorphous,
( 1 9 5 6 ) - t h a ti s ,d : 4 . 2 0 I, : 1 5 ;4 . 1 5 ,1 3 ; 3 . 8 9 , 7 ;
3.60,7-and by Papeeet al (1958)-thatis, 4.205,m; reflections."They found that the unknown mineral
4.153,m; 3.880,m; 3.600,m. This is confirmed "seemsto occur ubiquitouslywith dawsonite,"and
gibbsiteor bayerite,both AI(OH)', as the
graphicallyby Schoenand Roberson(1970),whose suggested
SmithandYoung(1969)alsocited
mineral.
unknown
Figure I clearly shows these four peaks for
ashaving"selecand
Hollingshead
Schmidt-Collerus
nordstrandite,but not for gibbsiteand bayerite.
oil shale
in
a
dawsonitic
this
mineral
enriched
tively
As Table 2 shows, these four peaks are well
gradient
detecting
this
centrifugation,
by
density
representedin the three patterns of the Colorado
were
unThey,
too,
:
analysis."
by
thermal
enrichment
4.20),
nordstranditeexcept,possibly,the first (d
idennot
specifically
it.
Although
able
to
identify
which appearsin about half of a dozenpatternsof the
Colorado nordstrandite.In some patternsoa dark tifying the mineral, Smith and Johnson (1967)
to be thoseof an amorphousor
band in this region may obscureweak reflections; showedits properties
form
of AI(OH)3.As a matterof
X-ray
amorphous
however,in others,suchas the one citedin Table I, it
material
is termed "gibbsite" in
convenience,
the
is absent.
analysisof bulk
their report.Ordinarydiffractometer
ChemicalAnalyses
samplesof complexcomposition,suchas oil shale,
particularly
Becauseof the extremethinnessof the films of may not revealsomeminor constituents,
nordstrandite in the fractured rock, wet-chemical if they occurin crystallitesof extremelysmall dimenanalysis of the nordstranditewas not possible. sions. The possibility may thereforebe considered
However,two samplesfrom 1087feetwereexamined that occult nordstrandite,whoseexistencein these
has beenshown,is the aluminumhydroxby emissionspectrography,
and one from 1154.4feer sediments
was examinedby the electronprobe. (Three X-ray ide postulatedby Smith and Johnson(1967)and
powderpatternsof the last sampleare givenin Table Smith and Young (1969). Neither gibbsite nor
2). Three such semiquantitativeanalyses,each in- bayeritehas beenobservedin the Green River Formineralogical
dicatinga compositionessentiallyAl(OH)a,aregiven mation,despitemanyyearsof intensive
288
MILTON, DI'YORNIK, AND FINKELMAN
Tlsr-r l.
X-Ray Powder Diffraction Data for Nordstrandite,Gibbsite,and Bayerite
Nordstrandite
Sarawak
ll,athaway and
Schlanger
<L962" L965)
Wall and others
(L962)
Davls
d (i)
rlrL
d (i)
rlrL
rs r i r
4.789
100
q. t6
v8
4.80
4.5L
4.322
4.207
L2
10
4.33
4,205
s
s
4.J4
4.L56
7
4.r53
s
3.887
3. 6 0 0
4
4
3,886
3 .6 0 0
3.429
4
5.42>
--
-:
cibbslte
Jaulca
Colorado
and H111
(1973)
Thls paper
(pattern C)
2.663 < I
3.140
3.O23
2.849
2 . 70 4
d(i)
r/rt(obs.) d(i)
llrt
I.L>)
DA
100
7
25
22
4,19L
WA
f,-.rt, ioo.o
llrrt
;;
4.320
27.0
4.18
3.92
L7
L2
4.L52
na
4.205
4.L60
18.0
L2,0
E
3.62
10
3.879
3.581
w
w
3.888
3.609
1 1, 0
8. 0
E
3 .5 5
3.46
3,427
5.0
5.Jtv
w
c. z5
tt
E
XnPD 12-460
Bayerlte
SWEneElC
nil
zo-rr
Rothbauer and
others (1967)
rlrL
d(i)
rlrL
4.82
100
4,71
90
4,34
40
4,35
70
3,35
10
6
3,29
< 2
J . J T
3.24
w
w
bw
:_
3.04
2.86
3.031
w
_:
3 .0 2 8
2.848
2.7L0
3 .3
3.0
2.5
( 2, 5 0 1 )
2,480
2,455
1.0
L2.0
8.0
3.L7
8
3. 08
4
1_"_:'
2.699
4
2.53L
2.5L0
< 2
< 2
Z.OJT
2.562
2.497 < I
2,480
3
2,450
1
(1970)
d (1.)
--
2
2
I
Boemne
i t rt l
\4/
3.19
3.022
2.850
2.704
.
sJm.neEac
SyntheElc
2 . 4 79
2,49
10
2,46
7
w
bn
2.46L
w
2.445
2.40q
2.44
L5
2.430
2.392
2,349
2,263
9
< 1
15
2.392
2.330
2.26L
s
w
2.40
25
2,27
31
2.382
2.335
2.28L
mg
w
nB
2.225
2.L48
1
z, zLt
2,L48
2.097
2,074
1
2.033 < 1
2.0L6
?'_o'u
2.393
2.333
2.27L
a
2.02
22
2.003
na
27.0
5.0
29.0
2,37
20
2.28
4
J. u
2.23
6
2.222
2.L5
8
2.186
2.168
2.L64
2. L56
2.03
L2
z,!40
z.)
2.LL3
1.6
2.074
3.0
2.0L5
(1.991)
24.0
2.0
L.975
1.0
L.982
L.9434 <
L
< 2
z. 5)o
+
100
2.073
1.993
1.98
r, 959
L.939
z
1
0q
10
1.983 < 4
2
1.969
1
L.945
2
1,917
1.9008
8
1.899
1,90
19
1.887
ma
1:rrrr.__t
1.8017 <
I
L,902
(L.877)
19.0
2.O
1,821
1. 8 0 4
2.0
3 ,0
L,784
1.715
I.704
1.668
1.653
13.0
1.0
2,0
4.0
3.0
1.632
1.5
I.
I.
1.90
8
1.904 < 2
2
1.835
1.78
II
1.802
w
OIO
1 .5 9 8
r.572
1 .5 5 0
U
5.0
4,0
1, 0
!'_t'u
L . 79
L . 74
10
r0
r.67
r.b5
10
4
I.OJ
Z
il*
4
1.57
2
L.765
L.723
1.595
1.688
1. 656
<
2
40
2
2
2
2
L.646
L.64L
2
(p1ue 39 llnes
to 1.125)
289
NORDSTRANDITE FROM THE GREEN RIVER FORMATION
Tlnln l.
Continued
llathaway and
Schlanger
(1962,1965)
Wall
4 dl
rlrL
d (i)
ilrtt
4
t.477
4
and others
<1962)
:rlrt
Colorado
Jamlca
Davls
d (i)
Beyerlte
-SynEEEEI--
Glbbslte
Nordstrandite
sarawak
and H111
( 1 9 73 )
rlrL
Thls peper
(pattern C)
a (l)
1,486
L.477
I .4395
L.435
rl rL
Synthetic
Syathetic
ioemne
(1970)
d(i)
r/rt(obs.) d(i)
L.547
L.5L7
6.0
7.O
L,479
1.465
5.0
2.O
L.44L
1.430
L.404
1.388
L.370
1.365
L4.O
5.0
3.0
1.5
1.0
0.6
XRPD 12-460
1.55
tlrt
)RPD 20-11
Rothbauer and
othera (1967)
d(l)
r/rr
2
wlt
w
study.Bayeriteis reportedonly from a singlelocality clusion that nordstrandite in nature forms liom
in Israel(Grossand Heller, 1963).
prior-formedbayeriteunderalkalicratherthan acidic
Maric (1967-68),describingthe Croatian nord- conditions.
strandite,found a strong exothermpeak at 3l0oChesworth(1971)reportedthat aluminum-mer340o, indicating nordstranditeor gibbsite,which cury amalgam reacts with 2M NaOH at atmocannot be distinguished
by their thermalbehavior. sphericpressureand 30oC to give boehmitewith
A peak at 500o was attributed to boehmiteformed nordstranditein a 408 hour run, and with concen(by loss of hydroxyl)from nordstranditeor gibbs- trated NHTOH, sametemperatureand pressure,to
ite. Similarly, Hathaway and Schlanger(1965,p. give nordstranditein a 48 hour run.
1032)noted that "The D.T.A. of nordstranditeis
Geochemistryof Nordstranditeand
very similar to that of gibbsite and is of limited
AccompanyingMinerals
diagnosticvalue." Lodding (1969)has shown that
gibbsite dehydroxylateswhen heatedat a constant
Goldberryand Loughnan(1970,p.489),whendisrate, part becoming boehmite (AIOOH) at about
cussingthe originof theNew SouthWales,Australia,
250oC, the remainder becoming Al2O, between
dawsoniteand nordstrandite,admittedthat the for250'C and 330oC.Smith (personalcommunication,
mation of the dawsoniteis "far from understood";
1970)has found that syntheticnordstranditebehaves
but accountfor the nordstranditethus: "nordstransimilarly.
dite.
as rims around the marginsof dawsonite
Synthesis
nodules suggeststhat it is a secondaryproduct
(Van Nordstrandet flormedthrough loss of soda from the latter minNordstranditewassynthesized
in 1962,and sincethen eral. . .
al,1956)prior to its discovery
by others who have also publishedX-ray powder
r'
+ \1,T.?*o,"'
* H'o=
data. Frisch (1965)found that grindinga-AlrO3in NaArcoa(oHL
"*l59,Tlil"
water produceda surfacefilm of nordstrandite.
The same equilibrium equation is proposedby
Schoenand Roberson(1970,p. 43), reviewing
prior syntheses,
1974)toexplainthe
concludedthat nordstranditeforms Smith(personalcommunication,
"from bayeriteduring aging at intermediateto high excess of acid-extractable alumina consistently
pH values,"bayeritebeing metastable.
Gibbsiteis appearingin analysesof Coloradodawsoniterocks
formed at a pH lessthan 5.8,bayeriteat a pH greater (Smith and Young, 1969;Young and Smith, 1970).
than 5.8. The alkalic environmentof the Colorado He suggeststhat Al(OH)s was precipitated (as
nordstrandite(in a dolomitic marlstoneseriescon- nordstrandite)from strongly basic lake waters
taining dawsonite,analcite,nahcolite,and other chargedwith Na+, COr'-, and aluminateion. In the
sodicminerals)supportsSchoenand Roberson's
con- water trappedin the sediment,the increasingcon-
290
MILTON, DWORNIK, AND FINKELMAN
Teet-r 2. Three X-ray Diffraction Patternsof
Nordstranditefrom Colorado*
(a) orlm
(u) crlv
Ig
rtt
a
\
vr
"\
vtt
VVE
\.Tt,
lo'*
llr.1o
3.829
3.176
3.335
3. Oll+
wfl
2.#r
vvw
2.694
E
2.4n
(e) eo/rr
IA
Y
g
l+.80
l+.32
l+.r85
n6
7.r55
\.79r
4 .3 3 r
v
4r r>o
!a
4.Lr2
\n/w
vw
wv
3.8n
T
ws
3. 588
3.316
!04
vvg
r
wtf
3.tt9
3.581
3.379
vvY
? n?1
lmw
2.5,62
2.3u5
wr'
!3
z.\6r
P.W
Ytt
2.218
\na
&s
2.33'
2.28L
w
2.W7
2.371+
vs
s
ng
2.67
2.On
oll
1.9O1
r!6
trut
2.0o3
1.8s1
vh
1.789
I.72I
x
1.802
1.5r_1
r.468
\rw
wv
r.485
r.4n
vt/v
I.t+3i
vfl
rlt
v
vh'
r.9fi
r.ryz
DI'
vYlr
wg
r^*b
vgtt
t.b9
L.l+11
r.332
r.289
r.ryz.,
vrY
r.r82
vc
I.1l+5
r.ol+o
r Sinclair Cross V No. I well, at 1/54.4
feet.
centration of CO, arising from organic matter
caused the reaction
NarCO, + HrO + CO, -
responsible
for "excessalumina"in the GreenRiver
analyses.
Hay (1970)derivedtheGreenRiverdawsoniteby a
differentmechanismfrom that whichhe proposedfor
the OlduvaiGorge(Tanzania,Africa) dawsonite.For
the GreenRiver,he proposesan originby reactionof
analcite(or another zeolite)under high Pgs, determined by equilibriumwith nahcolite
NaAlSi,o".H,o * Co,---+
* NaAl(OH),Coa
?::9,
In OlduvaiGorge,dawsonite(and analcite)forms
from alteration of halloysite in mudflow deposits
thus:
AlrSirOs(OH)o
f 2Na* * COr'bol loyei te
-+ NaAlS.izoo.
H,o * *"*lSo""Tl):"o,
Elsewhere in Olduvai Gorge, in an "alkali carbonate ash bed" Hay (1970, p. 251) suggestedthat
dawsonite and natrolite form from chabazite and
analcite; in a similar bed, nepheline is given as the
source of dawsonite and natrolite. Hay does not
consider Al(OH)s (gibbsite specifically) as having
'any role in the formation of dawsonite.
It may be concluded from the foregoing citations
that the geochemistryof thesesubstancesis to a considerable degree a matter of conjecture.
Goldberry and Loughnan discussedin some detail
many sulfate minerals, which they termed secondary,
from the Bary Formation of New South Wales,
Australia. However, they suggested that the
glauberite (NarCa(SOn)r) was formed by reaction of
precipitatedmirabilite (NarSOo.l0HrO) with gypsum
(CaSO..2HrO), and that dawsonite has replaced
Teslr 3. Analyses
"t T:ilrffi:aite,
2 NaHCOg
with an accompanying shift in pH from near 1l to
about 9 (Smith, 1974). Under these conditions, the
aluminate ion precipitates as Al(OH)s. As representedin the following equilibrium equation (Smith,
t974),
NaHCO. + Al(OH)a s NaAl(OH)rCO3 + HrO
the bicarbonate combines with the aluminum
trihydroxide to produce dawsonite. This is the
(reversed) Goldberry-Loughnan equation. Smith
suggests that since nordstrandite is the phase of
Al(OH)s that is thus formed, this mineral. rather than
the commoner gibbsite as previously assumed, is
Spec trographic*
2 Samples fron 1087 ft
X-ray film
378
386
>10f
3
3
1
0.1
A1
sl
Ca
Fe
K
0,03
0,03
Ba
Cr,Tl,Cu
*Cfaude
**Robert
Rio BlancoCounty,
Probe**
Electron
Samples from 1054.4
895
>10
3
0.1
0. 003
30
tu3
<L
<1
<I
0.01
0. 01
0.01
<1
<I
0.01
Waring, U.S. Geologicaf
Surveg.
Finke]ren,
U .5. GeofogicaT
Suxveq;
semi-quanxitative
energg dispersive
analgsis.
fin
^ar^anf
ft
NORDSTRANDITE FROM THE GREEN RIVER FORMATION
291
this glauberite,and in turn has been replaced, Editors.AcademicPress,New York, London, pp. 1239-1250.
wholly or in part, by nordstrandite.Nothing in Mrnrc, Lure (1967-68)Nordstranditi gibsit (hidrargilit)u terra
Vjesnik,2l,28l-291(with summary
the Green River dawsonite-nordstrandite
occurrence rossikarstaDinarida.Geol.
in French).
suggestssuch a mechanism.Sulfatemineralsin the
NAnnv-Szlso, I., ero E. Pnrrn (1967)Nachweisvon NordstranGreen River Formation, other than weathering dit und Bayerit in UngarischenZiegeltonen.Acta Geol. Acad.
productsof iron sulfides,are extremelysparse.
Sci Hung. ll, 375-377.
Acknowledgments
We are indebtedfor helpfulcommentsfrom MichaelFleischer,
John L. Haas, and E-an Zen (U. S. GeologicalSurvey),Adolf
Pabst(Universityof California,Berkeley),
JohnWard Smith(U. S.
Bureauof Mines),and, for unpublisheddata,to VincentG. Hill
(Commissionof Mines, Jamaica).This work was supportedby
National ScienceFoundationGrant GA-4433.
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Manwcript
receiued, August 9, 1974; accepted
lor publication, October 22, 1974.