American Mineralogist, Volume 70, pages 193-j96, I9E5
Fingerite, CurrOz(VOt)et a new yanadium sublimatefrom lzalco volcano, El Salvador:
descriptivemineralogy
JosN M. HucHes
Miami
Department of Geology
University, Oxford, Ohio 45056
aNo C. G. Haoruecos
Geophysical Laboratory
2801 Upton Street, N.W., Washington, D. C. 20008
Abstract
Fingerite, cu11o2(voa)6,o h€w copper vanadatemineral, has been discoveredin the
summit crater fumaroles of Izalco volcano, El Salvador, Central America. The mineral,
which occurs with thenardite and euchlorine, forms as a sublimate product from the
volcanic gases.Fingerite occurs as euhedral, subhedraland anhedralcrystals up to 150pm
in greatestdimension.
Fingeriteis triclinic, PT,a :8.1576(6), b = 8.2691(5),
c :8.0437(7)A, u: l}'t.t44(5),
F : 91.389(7),y = 106.441(5)'and V = 493.84(0A3.ttre five most intense lines on the
Gandolfipattern are 6.48(100;Tt0, 0tT;, 3.894(60;200,120),3.042(80;otz, t20),2.822(70;
122,2-12)and 2.025(70 ; 203).
Fingerite is black with a metallic luster and opaque.The calculateddensity of fingerite is
4-776gnlcc, z : l.In reflectedlight in air, fingeriteis mediumgray, non-pleochroicand
exhibits 2 extinctions per complete rotation of the stage. The reflectance of randomly
orientedgrains in blue-filteredwhite light in air is 2l-rTVo.
Milligram amounts of the mineral exist. Type specimensare on deposit at the National
Museum of Natural History, Smithsonian Institution and the Geophysical Laboratory,
CarnegieInstitution of Washington.The mineral is namedin honor of Dr. Larry W. Finger,
Geophysical Laboratory.
Introduction
Locality and occurrence
Naturally occurring Cu11O2(VOa)6
has been discovered
Izalco volcano is a basaltic composite cone that has
in the fumaroles in the summit crater of Izalco volcano,
been intermittently active since its birth in 1770. The
El Salvador, Central America (13'49'N; 89'38'W). The volcano rises to an altitude of 1965m, with 650 m relief,
authors are pleasedto name the new mineral fingerite in
and has an approximate volume of 2 km3. The geology of
honor of Dr. Larry W. Finger of the GeophysicalLabora- the volcano is describedby Meyer-Abich (195E),Rose
tory, Carnegie Institution of Washington. Dr. Finger is
and Stoiber (1969)and Stoiberet al. (197!.
well known for his work in the fields of mineralogy,
In 1963 the first-known, high-temperature vanadium
crystal chemistry and crystal physics, and has served mineral was discoveredin the summit crater fumaroles of
both the Mineralogical Society of America and the InterIzalco volcano. Since that time, the volcanic gasesand
national Mineralogical Association through his service on
sublimatemineralshave beenextensivelystudied.Severseveral committees.
al new vanadium minerals have been discovered at the
Type specimensoffingerite have beendepositedat the site, including bannermanite [(Na,K)*Vl* Vl1*O,r;
Geophysical Laboratory, Carnegie Institution of Wash- Hughesand Finger, l983al, shcherbinaite(VzOsiHughes
ington and the National Museum of Natural History,
and Finger, 1983b),and three vanadatesin the system
SmithsonianInstitution. The total amount of the new CuO-V2O5. Fingerite is the fourth sublimate mineral in
mineral on hand is a few milligrams. The mineral and this chemicalsystem,joining stoiberite(Cu5V2O16;
Birnie
mineral name have been approved by the Commissionon
and Hughes, 1979), ziesite (B-Cu2Y2O7;Hughes and
New Minerals and Mineral Names, LM.A.
Birnie, 1980),and Cu3V2O3(Christian and Hughes, in
0003-004x/85/0102-0193$02.00
193
r94
HUGHES AND HADIDIACOS: FINGERITE: DESCRIPTIVE MINERALOGY
prep.). It has beendemonstratedthat the mineralsformed
as sublimatesfrom a vanadium-bearingvolcanic gas, at
temperaturesup to 760"Cand oxygen fugacities of 10-3'5
bar (Hughesand Stoiber, 1985).
Fingerite is found in the "Y" fumarole (Stoiber et al.,
1975,Fig. l), one of five major fumaroles in the summit
crater of Izalco. The mineral occurs as black grains up to
150pm in greatestdimension. Fingerite was found in the
outer sulfate zone of the fumarole, indicating a sublimation temperature between lfi) and 200"C (Stoiber and
Rose, 1974). The mineral is intimately associatedwith
thenardite (NazSOr) and euchlorine [(Na,K)zCuro
(SO4)r0(OH)7'l0HzOl; it is commonly intergrown with
the latter.
Table l. Microprobe chemical analysesof fingerite
f*
CUO
3 9 . 6 5( 4 0 )
v^o-
2*
3
s9.s3(33)
51.59
39.67(18)
38.4r
r00.00
Total
of
7 analyses
Z. *, ot
15 aalyses
1. f
of
type crystal
of
3 cryslals.
for
chenical
Fomula
analyses'
(o=25) |
ctlo.oot.:(voc)6.2
3. Ideal cutto2 (vo4) 6.
* One standard
deviation
in parentheses.
System CuGV2O5
The first study of compounds in the CUO-V2O5binary
systemwas undertakenby Brisi and Molinari (1958),who
identified five incongruently melting compoundsbetween
the CuO and VzOs end members (Fig. l). The phases
reported by Brisi and Molinari have CuO:V2O5 molar
r a t i o so f l : 1 , 2 : 1 , 3 : 1 , 4 : l a n d 5 : 1 ( s t o i b e r i t e )S. u b s e quent studies have been undertaken on both specific
compoundswithin the binary system and phaserelations
among the various compounds. For example, MercurioLavaud and Frit (1973)demonstratedthat a high temperature polymorph of the 2:l phase (ziesite, ftCn2Y2Ol)
exists above 712"C.Fleury 0966, 1969)redeterminedthe
phaserelations within the system and was able to reproduce all of the compounds except CurVzOqreported by
Brisi and Molinari.
Fingerite was first identified as a new mineral by
comparisonof its diffraction pattern with that of CuaV2Oe
(rcros 16-420;note that the most intense peak of rcros
16-420is listed as 3.524, whereasthe original publication
lists the peak as 3.594). The similar patterns suggested
that fingerite is the natural analog of Cu+VzOq.As shown
Brisi
subsequentlythe formula of fingerite is Cu11V6O26'
and Molinari (1958), however, never analyzed the reaction products in their study of system CuG-VzOs. Their
proposed chemical formulas were derived from the ratio
of the system components at which the most intense
powder diffraction peaks of each product was observed.
This error in chemical formula perhaps explains the
inability of Fleury 0966, 1969)to synthesizethe CuaV2Oe
phaseof Brisi and Molinari.
is preferred for fingerite
The formulation Cu11O2(VOa)6
to emphasizethe fact that it is a member of the class of
vanadatesbasedon tetrahedralVOa $roups, in contrast to
the vanadium bronzes such as bannermanite,which have
sheet structures based on linked, distorted VO6 octahedra. All the compoundsin Figure I are tetrahedral types:
Cu(VOr)z (metavanadate,probably tetrahedral chains);
Cuz(VzOz) (divanadate); Cur(VO+)z (orthovanadate);
CurrOz(VOn)o(fingerite); and CusOz(VOa)2(stoiberite).
ChemistrY
Energy dispersive chemical analysesof fingerite were
performed with a rpor seu/Microprobe. The analyses
showed that among elements withZ > 9, only Cu and V
are present. Quantitative wavelength dispersive analyses
of fingerite were performed with rnol 35 and unc400
vzos
electron microprobes. Cu metal and V metal were usedas
Mol % CUO
standards.The results of the analysesare summarizedin
Fig. l. Phase diagram of the system CuO-V2O5 (after Brisi
Table l.
and Molinari. 1958). Similar diffraction patterns of fingerite
Calculation of the empirical formula suggestedthat the
(Cu11V6O26,
3.67CuO:V2O5)and the CuaV2Oe(4 CuO:VzOs)
CuaVzOg(CuO : VzOs : 4 : l) formula of Brisi and Molinari
phase of Brisi and Molinari suggestthat their determination of
(1958)was incorrect. On the basis of density, volume/
phasecomposition is in error. The high-temperaturepolymorph
oxygen atom, and the empirical formula, a formula of
of the 2CuO:V2O5 phase (FCrtz\zOz, ziesite) was not recog(CuO:VzOs -- 3.33:1) was proposedfor the
CuroVoOzs
phase
5CuO:V2O5
The
study.
Molinari
and
in
the
Brisi
nized
A subsequentstructure determination, denew
mineral.
=
(CusVzOro) stoiberite.
HUGHES AND HADIDIACOS: FINGERITE: DESCRIPTIVE MINERALOGY
r95
scribedin the following paper (Finger, 1985),demonstrat- 8.0437Q)4, d = 107.144(5)', = 91.389(7)","y :
F
ed that the correct formula for fingerite is Cu11V6 106.441(5fand Y: 493.E46)43.
O26[Cu11O2(VOa)5].
Analysis 2 in Table I is thus in error
Frecessionphotographs demonstratedthat fingerite is
by -3.8% and +2.8Voof the amount present for CuO and triclinic, space group Pl or PT. The structure study by
V2O5,respectively.
Finger to be reported subsequently demonstrates that
fingerite crystallizes in spacegroup PT.
X-ray crystallography
Physical properties
Diffraction patterns of fingerite in vacuo were obtained
with a 114.6 mm Gandolfi camera with Ni-filtered. Cu
Fingerite occurs as euhedral, subhedral and anhedral
radiation. Intensities were visually estimated. The in- crystals up to approximately 150 g,m in greatest dimendexed Gandolfi pattern, together with the pattern calcu- sion. The mineral is black with a metallic luster. The
lated from the crystal structure, is presentedin Table 2.
streak of fingerite is dark reddish brown, similar to the
After definition of the reduced lattice by precession streak of hematite.
methods, precession photographs were taken with ZrCrystals of fingerite grow in both plateJike and equant
filtered, Mo radiation. Cone-axis and precession photo- habits. Figure 2 is an SEM micrograph of a twin intergraphs of the 0, I and2levels were taken along a, b, and growth of two plate-like twin members and
one equant
c. The axial parameterswere refined using 20values from
twin member; the figure shows the relationship between
the Gandolfi pattern, and these values were subsequently morphology and principal axesof the plate-like habit. The
confirmed in the structure work by Finger to be reported two plate-like twin membersare related by a 180"rotation
in the subsequentreport. Becauseofthe higher precision about [010].
ofFinger's data, those parametersare reported here. The
No cleavageswere observed in optical or SEM examiaxial parameters were refined from the positions of 20 nation of fingerite crystals.
independentobservations with 39. < Z0 < 54. measured
The calculated density of fingerite (MW : 1420.65gml
on a four-circle difractometer by the eight-reflection mol) is 4.776 gmlcc, Z = l. Sample scarcity prohibited
centering method of King and Finger (1979).The refined direct measurementof the density. Crystals of fingerite
unit cell parametersof the all-obtuse normal reoresenta- were observed to sink rapidly in methylene iodide (S.G.
tion of the unit cell area :8.1576(6), U : g.Zei\S\, c :
: 3.32 gm/cc). The density and volume/oxygen atom
Table 2. Calculated and observed powder patterns offingerite*
al(obs)
d(calc)
-
7,770
-
{.oJJ
7.53
5.48
7.528
6,\79
6,\7\
5.80
5.795
!.zsa \.735
3,891+ 3.885
3.882
3.517 3'639
3.512
3.r98
3,597
3.293(d)3.309
3,277
3.192 3.187
3.108 3.115
3.091
3.0\2 3,ol+\
3 .o l { o
3.020
2.901 2.898
2.822 2.830
2.820
e,7i3 2.7\7
l.lLO
Z. lro
2,7L6
2.668(d.)2.69\
2.680
2,666
2.5\3
2.633
I(obs)
10
r00
10
50
ou
ou
OU
10
t0
80
40
7O
u0
l+o
[0
I(calc)
3.8
'1.6
2.'
13.?
93.2
rt.8
55.r
20.5
1L.L
!!.1
23.r
20.2
59.O
5r.3
\7.5
r3,8
15.8
9.3
26.11
69.9
\2.9
81.8
2r.5
?8.r
6U,7
80.2
38.5
100.0
63.0
!7.1
29.2
20.8
h k I
q(006./
q(carc./
1o 0
o o l
010
rro
011
101
r I 0
200
fz o
Eor
111
211
102
201
10 2
22r
211
210
I 2 0
oL2
021
doz
r22
zTz
131
3 1 0
z td.
2 r 2
oi:
2tl
031
r30
2.52'
2.r7\
2.540
iobserred alata obtained froe 11!.6 m
veuu,
vlswl
lntelsity
estiuates.
structue .
2 q21
rtoos,
!o
6 lines,
2.52-2.fi
2.\t%
2,\66
z,t+j6
2.\\7
2.4].9
2.358
zo
2,328
c
tAa
c
aA1
z.z
2.OTO
2.O25
r.r+5
r.72O
r.688
1
q?1
L.)25
-
-
r
\o
I!
2.209
2.O5tt
2.O22
I .9Lr
L.7r7
r.585
1.588
(tt
!,)1)
50
?o
30
30
zo
20
20
r.tr89
1.1+86
r.40f
r.\62
1.1+10
1.358 7.357
1 .3 4 3 1 . 3 1 3
lio
20
r(cBfc,
hkl
31,3
,i.3
6\.2
r 2r
zlt
r f r
\6.2
\T.r
r7.7
39.r
o Ja
zd t
22L
L2 3
28.9
25.7
10.6
r3.2
r1.8
6l+.3
59.r
29.9
8\.3
77,\
12.r
26.1
rl+.8
33.r
L8.o
19.r
52.9
29.I
51.0
29,r
35'7
28.5
5.\
Gmdotfi c@ra,
Ni-fiLtered. Cu radiatlon,
Cslculated data obtained frcn the crystal
L22
2 2 0
o22
321
131
f ri
3 o z
o!3
r!1
203
5\o
303
rL5
z T tr
E l+I
2 l* 3
5 0 1
3 4 lr
2oZ
rt l
L 2 l+
3 l+ 3
\51
196
HUGHES AND HADIDIACOS: FINGERITE: DESCRIPTIVE MINERALOGY
References
a
Birnie, R. W. and Hughes,J. M. (1979)Stoiberite,Cu5V2O16,
new copper vanadatefrom Izalco volcano, El Salvador, Central America. American Mineralogist, 64, 941-944.
Brisi, C. and Molinari, A. (1958)Il sistemaossidoramicoanidride
vanadica. Annali di Chimica. Roma. 48, 263-269.
Finger, Larry W. (1985)Fingerite, CurrOz(VO+)e,a new vanadium sublimatefrom Izalco volcano, El Salvador: Crystal structure. American Mineralogist, 70, 197-199.
Fleury, P. (1966)Sur le systemeCuO-V2O5.ComptesRendusde
I'Academiedes Sciences,Paris, Ser. C,263,1375-13'17.
Fleury, P. (1969)Etudes sur les systemesV2O5ou Ag2O ou
Tl2O3 et sur les combinaisons interoxydes correspondantes.
Revuede Chimie Minerale,6, 819-81.
Hughes,J. M. and Birnie, R. W. (1980)Ziesite, ftCtt2Y2Ol,a
new copper vanadate and fumarole temperature indicator.
American Mineralogist, 65, 1146-1149.
(1983a)Bannermanite,a new
crystal Hughes,J. M. and Finger, L. W.
of a multiply-twinned
Fig. 2. SEM photomicrograph
with pNa*V6O15.
vanadate
isostructural
sodium-potassium
of fingerite,denotingb andc axesof thedominanttwin member.
6f4-641.
Mineralogist,
68,
American
Both the {100}and {010}pinacoidalforms are presenton the
Hughes,J. M. and Finger, L. W. (1983b)The crystal chemistry
dominanttwin member.Scalebar represents100microns.
of shcherbinaite,naturally occurring V2O5.American Mineralogist,68,1220-1222.
(18.994) of fingerite are both within the range of other Hughes,J. M. and Stoiber,R. E. (1985)Vanadiumsublimatesin
the fumaroles of Izalco volcano, El Salvador. Journal of
copper vanadates.
Volcanology and GeothermalResearch,in press.
reflected
light.
In
Fingerite is opaque in transmitted
King, H. E. and Finger, L. W. (1979)Ditrractedbeam crystal
light in air, fingerite is medium gray. The mineral is noncenteringand its application to high-pressurecrystallography'
pleochroic and randomly oriented grains exhibit 2 extincJournal of Applied Crystallography, 12, 374-378.
tions per complete rotation of the stage.
Mandarino, J. A. (1976)The Gladstone-Dalerelationship part I.
Determination of quantitative reflectance values was
Derivation of new constants.CanadianMineralogist, 14, 498hampered by the small grain size of fingerite and the
502.
extensiveplucking that resultedfrom polishing. Reflec- Mercurio-Lavaud, D. and Frit, M. B. (1973)Structure cristalline
de la variete haute temperature du pyrovanadate de cuivre:
tance in blue-filtered white light in air was determinedby
Cu2V2O7.ComptesRendusde I'Academiedes Sciences,Parcomparisonwith standards.Randomly oriented grains of
is, ser. C., 277, ll0l-1104.
fingerite were found to have a reflectance indistinguishH. (1958)Active volcanoes of Guatemalaand El
Meyer-Abich,
able from that of magnetite. Thus the reflectance of
Salvador. In Catalogueof the Active Volcanoes of the World
fingeriteis estimatedatZlt2Vo.
Including Solfataras, Part VI, Central America, p. 39-105.
The mean index of refraction of fingerite, calculatedby
International Association of Volcanology, Rome, Italy.
the rule of Gladstoneand Dale with the specificrefractivi- Rose,W. I. and Stoiber,R. E. (1969)The 1966eruptionof Izalco
ty valuesgiven by Mandarino(1976),is 2.124.
volcano, El Salvador. Journal of Geophysical Research, 74,
Sample scarcity and size prohibited measurementsof
3119-3130.
hardness.The mineral does not fluorescein short- or Stoiber, R. E. and Rose, W. L (1974)Fumarole incrustationsat
active Central American volcanoes.Geochimicaet Cosmochilong-wave ultraviolet radiation.
mica Acta. 38. 495-516.
Stoiber, R. E., Rose, W. L, Lange, I. M., and Birnie, R. W.
Acknowledgments
(1975)The cooling of Izalco volcano (El Salvador) 1964-1974.
from
This work wassupponedin part by grantPRM-8117456
GeologischeJahrbuch,13, 193-205.
theNSF (Hughes).Drs. JamesDavisandThomasLaskowskiof
Owens-Corning
Fiberglas,
Inc., arethankedfor theirassistance
The manuscriptbenein obtainingthe SEM photomicrographs.
fittedfromreviewsby Drs. HowardT. Evans,Larry W. Finger,
RobertM. Hazen.MalcolmRossandHattenS. Yoder,Jr.
Manuscript received, February 7, 1984;
accepted for publication, August 13, lgM.