UMOHOITE FRO\T CA},IERON, ARIZONA PBccv

THE AMERICAN
MINERALOGIST,
VOL 44, NOVEMBER_DECEMBER,
1959
UMOHOITE FRO\T CA},IERON, ARIZONA
PBccv-K.q,vHeurlroN* .q,wlPaur, F. Krnn, ColumbiaUnittersillt,
NeutYork l{. Y.
Agsrn,tcr
Studies indicate that the hydrous uranium-rnolybdate, umohoite, is a more widely distributed mineral than has been previously known. The original crystalline material was
found at Marysvale, Utah. Similar crystalline material has since been reported by Coleman and Appleman from the Gas Hills district, Wyoming. Recently, a new occurrence in a
fine-grained form has been discovered at Cameron, Arizona. A similar fine aggregate has
been recognized in recently coliected material from Marysvale. The identification of finegrained umohoite has also been confirmed from an undisclosed locality in the U S.S R.
The change in lattice dimensions under r-ray bombardment or variable conditions of
humidity and temperature has constituted a problem in the r-ray difiraction study of this
mineral. In order to overcome this difficulty, the adsorption of the large ethylene glycol
molecule into the water positions has been utilized to stabilize the umohoite structure. This
may be accomplished without destruction of the structure.
Three coexistent structural modifications are recognized in umohoite. These are designated Modes l, 2 and 3. The modes range in intensity of development as sholvn by r-ray
diffraction. In fine-grained umohoite (Cameron, fine Marysvale and U.S.S.R.) Modes 2
and 3 are better developed than Mode 1. In coarser Marysvale umohoite Mode 1is more
prominent than Modes 2 and 3. The coexistence in the same mineral of three systematic
sequencesof lattice variation (or modes), each exhibiting a range in crystallinity in response
to physical conditions, is an unusual mineralogical feature.
IwrnooucttoN
Umohoite was first discovered(Brophy and Kerr, 1953) in the Freedom No. 2 mine at Nfarysvale, Utah, where it occurs in distinct bluish
black plate-like crystals. Subsequently,Coleman and Appleman (1957)
reported a secondoccurrenceof crystalline umohoite aggregatesat the
Lucky ltlc mine in the Gas Hills, Wyoming.
During the investigation of uranium mineralization and associated
alteration at Cameron,Arizona, radioactiveblue-blacksooty massesand
carbonaceoustrash repiacementsat the Alyce Tolino mine were obtained
through the courtesyof NIr. Page Blakemore,Jr., geologistfor the Cameron Uranium Company. After a few days' exposureto the atmosphere,
a freshly broken surface of this material developsa bright blue water
soluble molybdenum efflorescencewhich is mainly ilsemannite. Such
areashave been found to contain umohoite, although the aggregatediffers in megascopicappearancefrom previously describedcrystals.
The three U.S. iocalities, as weil as an occurrencein the U.S.S.R.,
indicate that this unusual hydrous uranium-molybdate may be more
widespreadthan was consideredlikely at the time of the original dis+ Deceased.Seenote on page 1260.
1248
UMOIIOITE FROM ARIZONA
1249
covery. Knowledge of the existenceof several other localities on the
Colorado Plateau where secondary molybdenum is associated with
uranium suggeststhe possibility that further study may disclosean even
more widespreaddistribution of umohoite.
In the examination of the fine-grainedmolybdenum-uranium aggregate from Cameron,it was first found necessaryto re-examinereference
umohoite from \{arysvale. A major difficulty recognizedsince the originai investigationof umohoite by x-ray diffraction has been its tendency
to produce shifting reflectionsas the mineral losesor gains water during
r-ray bombardment.Kamhi (1959)in a restudy of individual l'rlarysvale
crystals carried on in this laboratory has shown that the lattice dimension normal to the flat flakes varies directly with ordinary variations in
atmospheric humidity, and inversely with increasing temperature. In
studying the Cameron material, it has been found necessaryto reexamine this unusual behavior of the I'Iarysvale umohoite. The study
has also led to the investigation of umohoite shown in the U.S.S.R.
exhibit at the first Geneva Conferenceon the PeacefulUses of Atomic
Energy (i955) and made available by Dr. A. P. Vinogradov of the
VernadskyInstitute of Geochemistryand Analytical Chemistry,Nrloscorv.
TecuNrque
In the examinationof umohoite,it has beenfound desirableto stabilize
the structure both during r-ray bombardment and under varying conditions of temperature and humidity. The analogy between the layered
structure of umohoite, as well as the range in states of hydration, with
the well-known shifts in basal spacing observed for the clay mineral
montmorillonite, suggestedthe use of ethylene glycol to establishlattice
stability. Umohoite crystals were chopped in distilled water in the
Waring Blendor, sedimentedonto a glass slide and then placed in an
ethylene glycol atmospherefor two days in a closedcontainer at room
temperature. The slide was then transferred directly to the Norelco
r-ray diffractometer (Fig. 1A.).
No fundamental change in umohoite appears to accompany the adsorption of ethylene glycol. No shift in reflectionsas shown in Table 1
and Figure 18 appeared,nor were new lines produced. The only differencenoted in the unglycolatedand giycolated spacingslies in the intensity of reflections.After r-ray bombardment a gradual return takes place
to the ungiycolated intensities (Fig. 1C) which would not be the condition if a change in structure had occurred. After glycolation of the
umohoite, changesunder r-ray bombardment and variations with temperature and humidity disappear. The presence of a large organic
moleculein the water positions seemsto support the surroundinglayers
PEGGY-KAY EAMILTON AND P. F. KERR
1250
ttttttltl
Frc. 1. X-ray
Marysvale, Utah.
difiractometer
patterns of oriented, coarsely crystalline
umohoite,
(A) Unglycolated material shows more intense Mode 1 reflections (:*) in contrast to
Modes 2 and 3 (:** and :***).
General hhl rcflections are shown without asterisks.
(B) Glycolated material shows the stabilized structure. Modes 2 and 3 are increased in
intensity while Mode 1 is decreased.Reflections 21.53 A and 18.99 A represent
increased intensities which merely cause a slight asymmetry in pattern A'
(C) The same sample following r-ray bombardment. The pattern returns toward type
A. Mode 1 shows stronger reflections than Modes 2 and 3. Asymmetry returns to
peak 16.99 A which correspondsto 16.$ A of A.
and inhibit their shift or collapsewith dehydration. It seemspossible
that the glycolated condition is in effect equivalent to a maximum state
of hydration.
Study of the glycolated crystalline umohoite #-ray diffraction pattern
(Fig. 1) showsthat there are three distinct first order (001) reflectionsin
I25I
UMOHOITEFROM ARIZONA
which values are respectively:(1) 16.83A, Q) 18.ggA and (3) 21.53A.
Each stands at the head of a successivesequenceof about 12 higher
order reflections all present in the same pattern. These groups are
designatedNlodes l, 2 and 3. Table 2 compares the calculated interplanar spacingswith observed diffractometer values for each of the three
modes.The intensitiesof each mode (Table 2) are determined independently and are based on the intensity of the strongestreflectionfor each
mode.
I t i s n o t e d t h a t e x c e p tf o r t h e w e a k 4 . 2 , 2 . 4 a n d 1 . 6 6 8A s p a c i n g si n
unglycolatedcrystalline umohoite, the Mode 1 (Fig. 1) reflectionsbefore
glycolation are stronger than those given by NIodes 2 and 3. The adsorption of the organic molecule appears systematically to strengthen the
intensity of I'Iode 2 and 3 reflections(Fig. 1), and to decreasethat of
Terr,a 1. X-Rev Drprnacrron Pownrn Dara non Coansnr,y
Cnvstellrltr
Uuonor:rn, Menvsvar,o, Uran
Cu radiation,Ni filter I:
(no glycol)
(no glycol)
(glycolated)
dL
1 6 .8 3
1 1. 7 7
r0.77
I .71
8.42
7. 1 9
6.23
5 .604*
5 .063
4.8M
4.619
4.393
4.208
3.2r8
3.173
3 .056
(glycolated)
dA
68
2
z
4
100
5
4
100
21.53
18.99
16.83
12.30
10.77***
9.50
842
7. 2 4
6.32*+
5.604
15
29
3t
5
100
IJ
66
83
4.74r
l9
2
3
4.370
4.208
3 588
3.349
26
4
5
3
31
3.162
3.054
29
5
74
3
10
5
* Strong Mode 1.
** Strong Mode 2.
*** Strong Mode 3.
dA
2.957
2.910
2.791
2
45
2.4t5
2
2 301
2.225
2.134
2.O92
2 034
1.991
1 860
| 825
r.779
z
z
53
3
J. /O/
3.349
I 5418 A
s
22
13
9
3
3
2
2.097
2.034
1.995
1.860
26
4
4
7
1.523
4
L
.1
J/
L
2
10
3
.)
I rl
z
1.696
1. 6 6 8
1. 6 1 3
1.521
z
I
2.924
2.795
2.720
2.704
2415
2.377
2.30t
J
J
6
PEGGY-KAY HAMILTON AND P. F. KERR
Tasrn 2. X-Rev DrrlnacrroN Poworn Derl ron Monns RococNzun ru Gr-vCoLATED
Coanser-vCnvsrar,ltNo lJuonotrn, Menvsvar-e, Uran
Cu radiation,Ni filter ).:1.5a18 A
Mode 3
dA
hhl
obs
(calc.)
001 21.53
I
Mode 2
dA
obs.
Nlode 1
dA
I
(calc.)
18
obs.
(calc.)
I
lftl
Mode 3
Mode 2
dh
obs.
dA
obs.
I
(calc )
I
dA
obs.
I
(calc.)
(calc.)
007 3.054 9
(3.08)
(2r. s7)
2.720 20
(2.70)
2.415 4
(2.40)
002 r0.77 100
( 1 07. e )
2 . 7 0 +9
(2.70)
z-Jl I
+
(2.377)
2.09733
(2 r0)
009 2.377 4
(2 -40)
6.32 100
( 6. 3 1 )
2.097 40
(2.10)
1.860 9
(r 37)
1.860 1r
(1 89)
( 1. 6 8 )
(r 72)
r.523 5
(1. s3)
(1. s8)
(1 40)
UMOI]OITE FROM ARIZONA
1253
I{ode 1. The latter, however,remainsthe strongest.After bombardment
of giycolated Nlarysvale umohoite (Fig. 1) Nlode 1 becomesmore intense and \todes 2 and 3 decreasein intensity. Although the 18.9 A
and 21.5 A glycolated spacings(Fig. 1) of Nlodes 2 and 3 (Table 1)
appear to be new, a definite asymmetry (Fig. 1) toward the lower angle-s
is present in both the unglycolated and glycolated bombarded 16.8 A
reflection.Since the (002) reflectionsat 10.7 and 9.5 A are much more
intense, it seemslikely that before glycolation these weaker (001) reflections are only strong enough to produce asymmetry. Likewise, the
3.7 A and 3.5 A Mode 2 and 3 reflectionsare weak in the glycolated
material and do not appear at all in the unglycolated specimen.The
1.860A line is believed to be principally a Xfode 1 (009) reflection,
a l t h o u g ht h i s i s a l s o t h e s p a c i n gf o r t h e M o d e 2 ( 0 . 0 ' 1 0 ) 1 . 9 0A r e f l e c tion. After glycolation this 1.860 A peak decreasesin intensity; after
bombardment it becomes stronger. This behavior is characteristic
of N{ode l reflections;so the peak is assignedto this mode. Likewise,
the 2.092 A reflection decreasesin intensity with glycolation, and increasesafter bombardment; so it is believedto be mainly Mode 1 (008),
although iL overlaps the (009) n'Iode 2 spacing.
Frrln-GnarNBo CarronoN Ultonorte
Microscopic Observation
Thin-section study shows that the Cameron material is blue-black,
opaque and contains no pleochroicblue-greenumohoite crystals as reported either by Brophy and Kerr (1953) or Coleman and Appleman
(1957).Scatteredgrains of angular qtartz are associatedwith prominent
bands of carbonate and pyrite. A few fragments of an unidentified secondary uranium mineral occur with the umohoite. Polished surfaces
of this black fine-grainedumohoite are isotropic. The apparent lack of
double refraction is attributed to the extremely finely divided state.
Associatedwith the umohoite are small cubesof cobalt-richpyrite which
enclosemarcasite.
X-ray Difraction
The identification of fine-grainedCameron umohoite dependslargely
on fr-ray diffraction data. The material was purified by stirring in cool,
distilled water in order to remove ilsemannite and any other water
soluble impurities. After the water soluble fraction was decanted,more
cool, distilied water was added to the residue,after which it was stirred
briefly and allowed to settie for a few minutes. Umohoite (Sp. Gr. 4.554.93) settlesfrom suspensionafter pyrite (Sp. Gr. 4.95-5.10)and before
qvartz (Sp. Gr. 2.653-2.660).However,no fine-grainedurnohoitefraction
1254
PEGGY-KAY HAMILTON AND P. F. KERR
was separated which was entirely free from quartz. Umohoite was next
sedimentedonto a glass slide so that a preferred orientation developed
(Brophy and Kerr, 1953).The slide was mounted directly in a Norelco
r-ray diffractometer.
X-ray difiraction investigation shows that the fine-grained Cameron
umohoite develops a preferred orientation and responds to ethylene
glycol as do the coarseMarysvale umohoite crystals.Unoriented samples
of both forms of umohoite give weak, diffuse patterns which improve
moderately after orientation. Thus the Cameron particles which are
estimatedto be a few micronsin diameter developa preferredorientation
which is similar to that of the coarsel,Iarysvale crystals which are tenths
of a millimeter in diameter. The adsorption of ethylene glycol stabilizes
the Cameron umohoite lattice in the same way that it does the \Iarysvale. Thereforethe r-ray diffraction pattern showsa consistentincrease
of Mode 2 and 3 intensities(Fig.2). After bombardment by r-rays, the
'opro,.
o1','
ltJ:
' "i
.991:,. z,s
'd
;uif/ T",r.'T#*,1
| 't' I 'r' /r
JJ .A1J J I IJ
T"l
tl
rTlilll
Fro. 2. X-ray
Arizona.
difiractometer
patterns of oriented fine-grained umohoite, Cameron,
(A) Unglycolated material shows characteristic Mode 2 and Mode 3 reflections However, these reflections are weaker than those of the coarsely crystalline umohoite
(Fig 1). Mode l reflections are weak or missing Quartz (Q) and pyrite (P) mask
several umohoite 00.1reflections.
(B) Ethylene giycol adsorption strengthens coexistent Modes 2 and 3. The strong
7.13 A reflection shows that in this specimen Mode 3 is more prominent than
Mode 2.
(C) In this glycolated specimen the intensity of the 6.32 A reflection shows that Mode
2 is stronser than Mode 3.
UMOHOITEFROM ARIZONA
1255
intensity of these modes decreasesto resemblethat of the unglycolated
specimen which also is similar to the behavior of the coarse crystals.
Although the Cameron diffraction patterns (Fig. 2) do not approachthe
definition and intensity of those of the Marysvale crystals (Fig. 1)'
they are simiiar.
The c-ray diffraction pattern of the Cameron umohoite (Table 3) is
characterizedby prominent Mode 2 and 3 reflectionsand weak or missing
Mode 1 reflections. This difiers from crystalline Marysvale umohoite
which has strong Mode 1 reflections,and relatively weaker Mode 2 and
3 reflections.In one Cameron specimen (Fig. 2C) Mode 2 is stronger
than coexistentNIode3 (Table 3); whereasin another,Mode 3 is dominant
(Fig.28). In the stronger X{ode 2 pattern it is interesting to note that
the 18.79A (OOt)\[ode 2 reflectionappearsonly after glycolation as in
the diffraction pattern of the coarsely crystalline lVlarysvale umohoite.
The intensities of the cameron Mode 2 and 3 reflectionsalso have the
samerelation to each other as those in the Marysvale crystals.However,
an unexplainedexceptionoccursin the Cameron strong Mode 3 pattern
reflectionis considerablystronger
(Table 3, Fig. 28) sincethe 7.1 A 1OOS)
than the 10 A (002) reflection, whereas in the Marysvale crystals (Table
1, Fig. 1) the 10 A spacingis stronger.
fn the Cameron material (Fig. 28) in which Mode 3 is prominent,
Mode 1 is fairly well developed. The following reflectionsfrom this mode
appear: (001) 16.83,(006) 2.S38and (007) 2.4fi A.Qtattzmay mask the
,i-.rg umohoite Mode 1 3.3 A line and pyrite the umohoite Mode I2.7 h
reflection. However, the strongest Nlode 1 reflection in the coarsely
crystalline umohoite at 5.6 A is missing in the cameron specimens.At
present there is no direct evidencefor the degreeto which Modes 1,2
and 3 may be developed.However, further investigationmay reveal the
relationshipof the oxidation state, hydration and uranium-molybdenum
ratio to the intensitiesof modes in umohoite.
X-roy Spectrograph
X-ray spectrographic analyses confirm the presenceof uranium and
molybdenum. These elementsare accompaniedin decreasingorder by:
silica, sulfur, iron, cobalt, nickel, arsenicand thaliium. The presenceof
thallium as an associatedimpurity is interesting, but the site of its
occurrence is unknown. Il is not Iocalized to any extent in the accompanying pyrite. The 3.4 A and 2.6 A (Fig. 2) unidentified r-ray diffraction reflections in the Cameron specimensmay be caused by a mineral
which contains some of these accompanying elements.It is worthy of
note that no evidencefor the presenceof molybdenite or molybdite was
found during the investigation.
t256
PEGGY-KAY IIAMILTON AND P. F" KERR
Tarr,u 3. X-Rlv Drlrnlctrox Powonn D.qra ron Frr.rrGnarNeo Gr-vcolereo Ulrorrorrn
Marysvale,
Utah
Cameron, Arizona
dA
001
(3)
(2)
(1)
oo2
(3)
(2)
(1)
003
(3)
(2)
(1)
004
(3)
(.2)
1 6 .8 3
10.04
006
(3)
(2)
(1)
(3)
(2)
(1)
40 r0.77
9.21
7 . 1 3 * * *100
6.36
40
4.619
(1)
00s
dA
30
7. 1 9
6.32**
4.643
4.254+s 100 4 263+a
J.//5
50
dA
20
18.99**
1 6. 6 7*
33
20
r0.77
33
100
3.2+l
2. 8 3 8
9.93
43
8.34
57
7. 3 6
6.34**
5.607*
43
57
43
43
7r
29
60
40
20
3 588
3 207
20
20
3 588
3 184
l4
14
3.631
3.184
.)/
100
3.07
2 795
2 459
13
27
20
3.104
29
3 051
2.769
43
43
2 712
t4
2 453+a 100
(3)
(.2)
2 . 7l 2 + p
2.412+P
80
80
2.704
2.415
20
2.+53
2.125
30
40
2.459
2.128
20
272
1.912+p
40
1.901
IJ
1.912+p 40
1.901
IJ
IJ
(1)
(3)
(2)
t4
4.350++x J/
3.767
+3
3 .349+a 100
008
0 . 0 . 1 0 (3)
(.2)
(1)
100
100
86
4 -263+a 100
5 . O/.)
43
3 .349+a 100
3 . 1 1 8 + P 50
2 778
30
2.453
30
(1)
19.62
l8.79
1 7. 0 1
40
(3)
(.2)
(1)
(3)
(2)
86
100
4.692
007
00e
dA
47
3 . 3 + 2 + a 100 3 345+a 100
J.J/4
7. 1 3 * * *
6.O2
s.604
U.S.S.R.
123+a
86
2.453+a 100
2 127+a
100
1.862
29
(1)
0 .0 .1 2 (3)
(2)
(1)
r.795
+J
r257
UMOHOITE FROM ARIZONA
AlorrroNer,
FrNB-GnarNno Ulronorrr
Locar-rrrps
Marysvale, Lttah
Recentiy,fine-grainedblue-blackumohoite masseshave been found at
X{arysvale, Utah. The occurrenceis significant as it establishesthe
presenceof this form of umohoite at the type locality. The nature of its
geologicrelation to coarselycrystalline umohoite requiresfurther study.
The intensity and definition of the r-ray diffraction pattern of this
material are similar to that of the Cameron umohoite. An oriented,
glycolatedspecimen(Fig.3, Table 3) showsI{ode 7,2 and 3 reflections.
Mode 2 is somewhatbetter developedthan \,Iode 3. Since pyrite is not
detected by r-ray diffraction in this fine-grainedumohoite, the Mode 3
3.104 (007) and 2.7 A (00S)umohoitereflectionsare not obscured.This
confirms the assignmentof these spacingsin the pyrite contaminated
Cameron material (Table 3, Fig. 2) to umohoite masked by pyrite. It is
interesting to note that as in the Cameron umohoite the Mode I 16.67
A (001) reflection is conspicuous,although several higher orders are
missing.
X-ray spectrographicanalysesshow that uranium and molybdenum
are accompaniedby iron, thallium and arsenic as contamination. AIthough thallium and arsenic impurities are not reported by Brophy
and Kerr (1953) in the coarsely crystalline I'Iarysvale umohoite, they
are associatedwith the fine-srained umohoite from Nlarysvale and
t*i*'",*r'ii t,t,g1-,1'.pp
1 692
Frc. 3. X-ray difiractometer porn-derpatterns of oriented and glycolated, fine-grained
umohoite from Marysvale, Utah and the U.S.S.R.
Marysvale material shows the characteristic coexistent modes which are identified in
the coarse crystals (Fig. 1). Mode 2 is somewhat better developed than Mode 3. Note that
as in one Cameron specimen (Fig. 2B1 the 16.67 A reflection is conspicuous, although many
Mode t higher orders are missing
The U.S.S.R. specimen has prominent coexistent Mode 1, 2 and 3 reflections. Therefore
this material more closely resembles the coarsely crystalline Marysvale umohoite (1B)
than the fine-grained specimens from Cameron and Marysvale.
1258
PEGGY-KAYHAMILTON AND P. F. KERR
Cameron.The associationof thallium and arsenicas impurities at both
localitiesmay have some geneticsignificance.
t/.s..s.R.
A specimenof fine-grainedumohoite from an unknown locality in the
U.S.S.R.was sent to the MineralogicalLaboratory, Columbia University,
by A. P. Vinogradov of the Vernadsky Institute of Geochemistryand
Analytical Chemistry, NIoscow.The specimenis very interestingsinceit
comesfrom a distant locality and suggeststhat umohoite may be rather
widespread.The fine-grainedblack umohoite matrix includesgranulesof
qttartz and unidentified vitreous dark brown material. A soft yellow
mineral occursas blebswhich are scatteredthroughout the specimenand
a s a c o a t i n ga l o n g o n e e d g e .
X-ray spectrographic analyses confirm the presence of uranium and
molybdenum in this material. Thailium and arsenicwere not detectedin
this fine-grainedumohoite. Iron, vanadium and lead are the principal
a c c o m p a n y i n gi m p u r i t i e s .
The r-ray diffraction pattern (Fig. 3, Table 3) of the oriented, glycolated black matrix is similar to that of the fine-grainedumohoite from
Cameron and Marysvale. Vinogradov (written communication) suggested that this specimencontained more than one form of umohoite.
An interestingfeature of the diffraction pattern (Table 3, Fig. 3) is that
it shows prominent n4ode l reflections.Coexistent n{odes 2 and 3 also
are well developedso that this umohoite is the most similar of the three
fine-grainedumohoitesto the coarselycrystallineumohoite from NIarysvale. Its tendencyto orient and respondto ethyleneglycol also is similar.
Thus after glycolation IIode 2 and 3 reflectionsare strengthenedwhereas
Mode 1 reflections are weakened. This is particularly evident in the
glycoiated (001) reflectionssince ltlodes 2 and 3 are present, whereas
before glycolation they appear only as a diffuse asymmetric reflection.
In addition to qtartz, reflections from an unidentified impurity are
present; however, they do not interfere with the identification of umohoite.
CoNcrusroNs
Umohoite adsorbsethylene glycol at room temperature and pressure.
This stablizesthe structure without a shift of interplanar spacingsor the
appearanceof new reflections.Once stability is established,there are no
lattice dimension changeswith varying conditions o{ temperature and
humidity. The presenceof the large organic moleculein the water positions seemsto support the surrounding layers and inhibit their shift or
UMOHOITE FROM ARIZONA
t259
collapse.It is possiblethat the glycolated condition is equivalent to a
maximum hydration state.
The presenceof three coexistentstructural modifications,Modes 1, 2
and 3, in umohoite is established.X-ray diffraction study shows that
each mode exhibits an orderly sequenceof reflections,and all three
groups appear in the same diffraction pattern. With the adsorption of
ethylene glycol there is a systematic increasein the intensities of l\llodes
2 and 3, along rvith a decreaseof Mode 1 intensities.This responseto
ethylene glycol is a characteristic property of umohoite which is useful
in identification, and should provide assistancein future structural
studies.
A fine-grainedform of umohoite has been recognized.It gives a weak
and somewhat difiuse r-ray diffraction pattern, but the same three
modes are present as in the coarsecrystals. l{odes 2 and 3 tend to be
somewhat more prominent than NIode 1 in the fine-grainedform, whereas
Mode 1 is stronger in the coarse crystals. The relative intensities of
lllodes 2 and 3 may vary, even among specimensfrom the samelocality.
Coarse umohoite crystals from Marysvale, Utah (Brophy and Kerr,
1953)and the Gas Hills area, Wyoming (Coleman and Appleman, 1957)
have been described. The occurrence at Cameron, Lrizona, of finegrainedumohoite establishesa third locality in the United Statesfor this
hydrous uranium-molybdate. The identity of an interesting specimen
of fine-grainedumohoite from the U.S.S.R.is confirmed.Thus, umohoite
is more widespreadin occurrencethan was known previously, and the
fine-grained form may be considerably more abundant than is now
known.
AcrNowr,rocMENTS
This investigationhas been made possiblethrough the cooperationof
the U. S. Atomic Energy Commission, Division of Researchand the
Division of Raw ltlaterials. The writers wish'to express partieular appreciation to Dr. Daniel R. Miller, Director of the Division of Research.
Umohoite specimensfrom Cameron,Arizona, were made available by
NIr. Page P. Blakemore, Jr. of the Cameron Uranium Company. Dr.
Gerald P. Brophy, Amherst College,has cooperatedby supplying umohoite crystals from nlarysvale, Utah. Dr. A. P. Vinogradov, Vernadsky
Institute of Geochemistry,I{oscow, U.S.S.R. has submitted a specimen
from Russia.Among the mineralogy group at Columbia University, the
authors wish to thank Dr. Otto C. Kopp and Nlessrs.William A. Bassett,
Edgar N{. Bollin and SamuelR. Kamhi for their helpful discussionsand
technical assistance.Mr. Arthur N. Rohl's observation of the polished
surfacesis appreciated.
1260
PEGGY-KAY HAMILTON AND P. F. KERR
Rnrrnrncrs
Bnorrrv, G. P., and Knnn, P. F. (1953), Hydrous uranium molybdate in Marysvale ore:
Annual Report from June 30, 1952 to April 1, 1953, U. S. Atomic Energy Commission,
RME-3046, 45-51.
Cor,ouax, R. G., auo Areluueu, D. E. (1957), Umohoite from the Lucky Mc mine,
Wyoming: Am. Mineral., 42, 567-6ffi .
Keunr, S. R. (1959), An x-ray study of umohoile: Am. Mineral.,44,920-925.
Knnn, P. F., Bnoenv, G. P., Danr,, H. M., Granr, J., .l,no Wooreno, L. E. (1957),
Marysvale, Utah, uranium area: Geol. Soc. Am. Special Paper 64,66-69.
Manuscript receil)edApr'il, 1, 1959.
Miss Peggy-Kay Hamilton, Research Associate in Mineralogy, Columbia University,
passed away on September 19, following an operation. Miss Hamilton was a Fellow of the
M i n e r a l o g i c a lS r c i e t y o I A m e r i c a .