827
The Canadin n Mineralo gi st(1996)
Vol. 34, pp.8n-$4(Ba,K,Pb)Na3(Ca,Sr)(Fe,Mg,Mn)
SIGISMUNDITE,
14Al(OH)z(PO4h2,
GROUP
A NEW Ba-RICHMEMBEROFTHEARROJADITEFROMSPLUGAVALLEY.ITALYFRANCESCODEMARTIN
Dipartimento di Chimica Stnrtturale e Stereochimica Innrganicq
Via Venezian 2 I, I-20 I 33, Milano, Italy

Universitd degli Studi,

CARLO M. GRAMACCIOLI
Dipartimento
di ScienzedellaTerra,Universitd
degliSndi, ViaBoxicelli23,I-20133,Milano,Italy
TULLIO PILATI
CentroCNRper lo StudiodelleRelazioni
fra Strutturae ReattivitdChimica,VinGolgi 19,I-20133,Milano,haly
ENRICOSCIESA
CN&ViaBotticelli23,I-20133,Milano,Italy
Alpinae Quatemaria,
Centrodi Studioper la Geodinamica

ABSTRACTa Ba-rich memberof the
The new mineral speciessigismundite(Ba,K,Pb)Na:(Ca,Sr)(Fe,Mg,Mn)r4A1(OH)2(POr12,
anojaditefamily, occursasgreyishgreenlumpsin phengiticquartziteat Madesimo,SplugaValley, Italy, associatedwith quartz,
is monoclinic,spacegrotp (2/c, with a 16,406(5),b 9.945(3),c 24.470(5)A, B 105.73(2)",apatite,andlazulite.SigismunditereflectionsF > 3o(/)l downto R = 0.066.
D,3.544 glcm3,n1u".**11.65(l).The structurehasbeenrefinedusing2846observed
This mineral differs fiom arrojaditeby the replacementof K by Ba the presenceof considerablecontentof I!9 in place oftransition metals, and vacanciesin the Na site, The strongestlines in the powder-diffraction pattem ld in A(I)(hkDl ate:.
3.010(100x424),3.178(sl)(206),2.678(42)(226),2.s23(27)(606),2.80s(2s)(318),4.st9(23)(rr4), 2.77s(21)(r34),
2.74l(21)(135),and2.732(21)(602).
Keywords: sigismundite,new mineral species,barium analogue,arrojadite- dickinsoniteseries,X-ray data,crystal-structurerefinement,SplugaVa1ley,Italy.

SoIvIN4AIRE
fartpaxriede
La sigismundite,nouvelleespdce
min6raledecomposition@aKPb)Na:(Ca,SrXFe,Mg,Mn)1aA1(OII)2(PO)r2'
la famille de l'arrojadite, dont c'est I'analoguebaryfdre. On la fouve en amasvert gdsafte dansune quartzite a phengib a
Madesimo,vall6e du Sp1ug4en Italie, en associationavecquartz,apatiteet lazulite. La sigismunditeest monoclinique,grcupe
1.65(1).Nousen avonsafftnd
b 9.945(3),c 24.470(5)A, p tOs.zl(z)", D,3.5M g/cm3,zl6oyen)spattalC2/c, aveca 16.406(5).
la structue en utilisant 2846r6flexionsobservdes[.| > 3o'(4] jusqu'] un r6siduR 6ga1i 0.066.Elle se distinguede l'arrojadite
lacunespar le remplacementde K paxBa, la pr6senced'une teneurimportanteen Mg i la placedesmdtauxde transition,et de^sdansles sitesoccup6spar le Na. lrs raiesles plus intensesdu spectrede diffraction X (m6thodedespoudres)Lden A(I)(hkDl
som 3.010(100)@fr),3.175(s!(206), 2.678(42)(226),2.s23(27)(606),2.80s(2sx318),4.519(23)(114),2.775(21)(134),
2.741(2r)(I 3s), et 2.732(2r)(602).
(Traduit par la R6daction)
Mots-cl6s: sigismundite,nouvelle espbcemin6ra1e,analoguebaryfhre, solution solide arrojadite- dickinsonite, donn6esde
diffraction X, affinementde la structuregristallins,vall6e du Spluga Italie.

828

TIIE CANADIAN MINERALOGISTINTRoDUCnoN

chlorite, feldspars and rare accessoryminerals (seebelow).
An interesting occurrence of phosphateswas
Sigismundite is associatedwith quartz, albite,
discoveredrecently near Madesimo, Spluga Valley, apatiteand ferrous carbonatespartly transformedinto
Central Alps, Italy. Thesephosphatesinclude lazulite iron oxides. Other primary metamorphicminerals inand apatiteas the most abundantrepresentatives,with the phosphate-bearing
quartzitic layersare K-feldspar,
minor amountsof svanbergite,woodhouseite, goyazite, rutile, schorl, barite, celestite,lazulite, woodhouseite,and crandallite.Of these mineralsosvanbergiteand goyaziteandpyrophyllite. Secondarymineralsderived
woodhouseiteareparticularlyrarein the Alpine region, from alteration of the above speciesare crandallite,
which emphasizesthe importance of the locality kaolinite, mitridatite and diaspore.In the fissuresand(Guelfi & Orlandi 1987,Bedognbet al.1995). Afew wgs of the quartzite, there are crystals of quartz,
yearsago,Dr. PaoloGentile, a mineral collector, gave apatite, svanbergite,barite, hematite, vanadinite andus a grayishgreenlump of an unknownmineral,found rare orange-redwoodhouseite(Bedogndet al. 1995).
in associationwith the other phosphatesdescribed Although a numberof similar outcropsof phosphateabove. Detailed examination confirmed the mineral bearing rocks occur in the vicinity (Val Scalcoggia,
to be a new Ba-rich member of the arrojadite Dair in BregagliaValley), sigismunditewas found at a
dickinsonite series;it is called sigismunditein honor singlelocality.
of Pietro Sigismund (1874 - 1962), a well-known
collector of minerals from Valtellina (especiallyVal
AppSARANcE
ANDPHysrcALPnopsnIFs
Malenco).The new mineralandthe mineralnamehave
been approvedby the IMA Commissionon New
The only specimenof sigismunditethat has been
Minerals and Mineral Names.The type material has found so far consistsof a small grayishgreenlump, up
been depositedat the Civic Museum of Natural to 4 cm in size,somewhatsimilar to massiveapatite,
History,Morbegno,Sondrio,Italy.
directly includedin the rock. The mineralis brittle, theThe very complexcrystal-chemistryof the arrojadite streakis white, and the luster is greasy.On inspecting- dickinsonite series has been the obiect of a thin section of the lump with a petrographic
considerable
investigation(Moore & Ito 1979,Moore microscope,a number of quartz grains are evident at
et al. 198L,Merlino et al. l98L). To provide an easy the border. intermixed with flakes of a colorlesscomparisonof the correspondingdatain the discussion phengite-like mica. The quafiz grains are partlyof the structure, the same labeling of the atomic idiomorphic where they are in contact witl
positionsusedby theseauthorshas beenadoptedhere sigismundite.The texture of accompanyingminerals
for sigismundite.
clearly indicates that the lump of sigismunditeis astructural relic with respect to the last stage of
OccURRENcE
alu PenecnNssts
deformationof the host rock. The individual crystalsof sigismunditeare imperfect,translucent,up to L cm
A single specimenof sigismunditewas found in across. These crystals are intensely microfractured,
phengitic quartzite at Madesimo, Spluga Valley, in some casesbeing ahnost completely divided into
northernItaly. The Tamb6and SurettaUpperPenninic subindividuals (about 10 - 20 W in size) slightly
nappesoutcropin the SplugaValley; they dip slightly misoriented with respect to each other. Within theeastwardand are formed by a pre-Perrnianbasement microfractures, quartz, apatite and an abundantconsisting of paragneissand micaceousschist, with carbonatesimilar to ankerite are invariably presenL
layers of amphibolite and orthogneissoand Variscan and replace a significant portion of sigismundite.
metagranitoidrocks. Theselappes are separatedby a Another distinct set of fracturesformed at a later stage
Perrno-Mesozoicmetavolcanicand metaseis also presentthroughoutthe sample;thesefractures
sequence,composedofmetarhyolite,quartzschistsand are almost perpendicular to the elongation of thechloritic-phengitic gneiss (Permian), phengitic sigismunditelump and are filled with a number ofquartzite (lJpper Peimian to Lower Triassic), and of other minerals,which cannot be identified by optical
calcite and dolomite marbles,gypsum and carbonate meansalone.
breccias (Middle to Upper Triassic). The quartzite
Within the lump, the original crystals ofbeds, derived from quartz-rich sandstoneswith sigismunditeshow rather straight borders, and often
conglomeratelayers, were formed during Alpine give rise to a sort ofpavement-likeaggregations.
ln onemetamorphism,and range from eclogite facies to caseonly, a crystal of comparativelyregularform wasblueschists facies, with a subsequentextensive noticed:its habit is elongate,andthe crystalfacesseem
retrogressionto tle greenschistfacies.The presumable to be almostparallel to the elongation.Underpolarized
presenceof organicmatlerin the sedimentsfrom which light, sigismundite shows a greenish yellow color,the sandstonesoriginated gave rise to the formation without appreciablepleochroism; no zoning wasofvarious phosphatesembeddedin the quartzites. observed,so that extensivevariation of the chemical
Theserocls contain abundantquartz,phengitic mica, composition is not expected,in agreementwith the

SIGISMUNDIIE. A Ba-RICH MEMBER OF TtlE ARROJADITEGROUPTABLE 1. ANALYTTCAL RESULTS FOR SIGISMUNDITE

829

E;ernnremel PnocsDUREs
Chemicalanalysis

Pzos
sio2
AlzQ
FeO
Mgo
MnO
Na2O

Kzo
BaO
Pbo
CaO
SrO
(Hzo)*
Total

4().50

0.u)

2.45
n.g
10.85
0.70
4.44
0.26
5.6E
0.76
1.09
0.86

39.88- 40.96
0.01- 0.03
2.40-2.54- 28.1126.86
10.64- 10,93
0.65- 0.75
4.32- 4.58
025 -0.28
5.61- 5.85
0.63- 0.89
z.ffi-2.20
0.99- 1.30

v7,34

EIVIPIRICALFORMULAs=6.sNa3.9(Ca6.79,Srs.2dt=6.9@as.n,K9.
12,Pbg.s7,516.s)2(Fq.12,Mg5.6,Mn6.a;r-1a.61A\.61(OH)z(Podrz
SIMPLIF]ED trORMUI,A:(Ba,K,Pb)Na3(Ca,Sr)(Fe,Mg,Mn)1aAl(OHbeOd
12-with the crysal
in agreement
ttre *ater conte"tfiasUe"ndeduced
struc,uredata*averageof 10 deeminatiotr on an ARLSEMQ electron
miuoprobe
voltage20 kV, smple currenton brais 15
Conrlitioml Accelerating
nA, ZAF conectionplogxamfromTRACOR.
Analydcalstaralsrds(nstunl standsnls):kaenuriteSi' Al, Mg'
Ca, K; spcsartineMn, Fe; aparie (USNM 104021'Jamsewichet
Pb; albiteNaal. 1980)P; celsianBa; celestiteSr; anglesite

Electron-microprobeanalysiswas doneon polishedgrain-mounts by using an ARL-SEMQ instrumentof ttre ttatlan National ResearchCouncil (C.N'R') at
Centro di Studio per la GeodinamicaAlpina e
Quaternaria,Milan. The standardsand operating
conditions are reported in Table 1; no extensive
variation in the compositionwas found in the different
points examined, ai shown in the third column ofiable 1. An energy-dispersionanalysis was also
performedusing a KEVEX Delta5 equipmentattached
io a 52700 Hitachi scanning electron microscope,
which hasprovedto be particularlyuseful in detecting
the lighteielements. By this method, in addition to
the pievious data, noticeable amounts of fluorine
were observed"so that some substitutionof the OH
group to(25)l by fluorine can be inferred, similarly to
wtraiis found in most ninerals of the arrojaditegroup'
The amount of qaler reported in Table I has been
deduced from the results of crystal-structurerefinementandis relativeto the purehydroxyl-rich end
member.
X-ray-dffiaction studY

The X-ray powder-diffractionpattern, recorded
using a Riguk" D/ilMAX diffractometer(Ni-filtered
Cufcr radiition, internal standard:quartz) is reported
in Table 2. The calculatedpattem was obtainedusing
the program POWLS80 (Will 1979); the unit-cellp*u."t"tt
refined ftom these data we reported inTable 3. A comparison of Table 2 with the(see,forresults obtained with an electron microprobe (see correspondingpowder pattern for anojaditg
that
shows
t98l)
et
al.
Moore
in
tO
faUte
instence,
fractures
The
above-mentioned
Table l, and below).
lowconcem
mostlyandminornareseemto indicatethe presenceof two different cleavage the differences
planes, one more distinct than the other, making an angle or weak reflections;for instance,the {002}forangleof about 110o.The interferencecolorsare very refrecdon (in our C2lc setting) is missing
isreflection
theconversely,
and,
{110}
sigismundite
of
the
those
with
compared
low, and can be roughlyastructure'thedetermineToquartzcrystalspresentin the samesection'For the only missing for arrojadite.
was
mm3
x
0.10
x
0.23
0.22
abo'ttcrystaf"measurin!
(seeextinction
theabove),
distinct crystal observed
angle is about 25o with respectto the elongation. mbunted on an Enraf'Nonius CAD4 diffractometer,< < 14'0"
Becauseof the presenceof considerableextraneous andtwenty-five intensereflectionswith 8.2 e
MoKcr
graqhite-monochromatedusingmaterial, and of the poor quality of the crystals, no were centeredparameters=fne
unit-ceU(),'
A).
0.71073
radiationbeobtained.
could
clear interferencefiguressetting
Owing to this inhomogeneityof the sarnple due (Table 3) were obtainedby refinementof theirrelating
matrixorientation
anwithtogetherangles,phasesmicrostructure,inthepresenceof several
to theA total ofa.reliable experimentalvalue of density could not be mJcrystafaxes to the dtffractometeraxes.
at roomcollected
wereintensities
ilffracted
5747
g/cmr.
No
3.544
is
value
calculated
obtained;the(mafmgg
scan-speed
variablewithlcanfluorescenceat 254 rm and 366 nm was observed. temperature
only an time for eachreflecuon:90 s), for -18 < h < 18,0 < kUsing a Raynertotal-reflectionrefractometeroof 60"'
averageindex of refractionn [= 1.65(1)]could be < 10 and 0 < I < 25, to a maximum20 angle
monitored
periodicallywerereflections
Referencethewithfavorablyverymeasured; it comparesn"ur.(= 1.639)from the Gladstone-Dale duringthe datacollectionto assessinstrumentstability'
corresponding
Lorentz,rule. Accordingto the criterionof Mandarino(1981)' The diffracted intensitieswere correctedfor
polarizationandbackgroundeffects.
the compatibilityindexis superior(-O.011).

830

TIIE CANADIAN MINERALOCISTTABLE 2. OBSERVED AND CALCIJLATED X.RAY POWDERDIFFRACTION DATA FOR SIGISMUNDITE
I

u\

uobs

rq@lc
-

h

k

I

d"b,

W

IABLE 4. FMCTIONAL ATOMIC COORDINATESFOR SIGISMUNDITE

I

I

88.3838.405

13372.9372.931

0 -2

5

7.528 1.572

5

I

-5

7

2.896

1

1-2

7

7.339 7.360

3

3

-2

20

2.8t9

2.819

75.8555.855

3

l

-8

25

2.805

2.807

5

5.470 5.481

I

3

4

2t

2.775

2.773

6

5.t85 5.t82

I

I

-5

21

2.741

2.740

6

0

-2

2t

2.732

2.129

2

6

42

2.678

2.679

202
2

04

l

I

-4

02054.961
3

|

-2

310

4.966

6

4.729 4.728

27

4.6424.47

332n2.6402.640
sr382.5922.592

0

2

2

15 4.566 4.5'75

l

I

4

23

220
2

2 -2

312

2.897

4.519 4.519

r

3

-6

13

2.570

2.568

74.t994.202

6

0

-6

27

2.523

2.524

15 4.155 4.153

0

4

0

13

2.486

2.483

83.984.005

|

3

-7

6

2.401

2.400

02483.7923.793

Muh

AI
Kl)

vz

da"

2

0

Atom

6

2

-2

8

2.393

2.392

3

I

-6

13 3.427 3.429

7

1

-6

t2

2.180

2.09

r

l

6

20

3.368 3.369

0

2

I0

9

2.125

2.t25

3

I

4

t6

3.279 3.282

2

2

t0

12

1.935

1.936

2

2

4

12 3.202 3.206

0

4

8

19

1.89?

1.897

2

0

6

51 3.178 3.181

8

2

2

t4

1.744

t.745

3

1 -7

13 3.097 3.099

6

0

8

14

1.74

t.739

4

2 4

I00 3.010 3.011

2

6

2

t4

t.582

I.593

0.000
0.583(?) 42299(3)x(2) I
0.1345(5)x(3) v2
0.000
x(4) 0.08q8) 0.000&4x) 0.050(8) 0.000
x(5) 0.485(2) 0.000M(1)0.437(5)o.?231(3)M(lx)
0.126(5) 0.205(l)M{2)
0.840(5)0.2118(l)M(3)
0.5r2(4)0.1071(2)M(4)
0.687(5)0.0215(2)M(5)
0.8e3(4)0.0338(r)M(6)
0.8e5(5)0.2036(l)M(7)
0.785(5)0.2r80(l)P(l)
0.620(8)0.1156(3)P(1x) 0.380(8) 0.0802(4)P(2)
0.1299(2)P(3)
0.r26s(2)P(4)
0.1033(2)P(5)
0.t294(2)P(6)
0.t43l(2)o(t)
0.0255(5)o(2)
0.r l r5(5)o(3)
0.1480(5)
o(4)
0.620
0.1808(8)O(4x) 0.380
0.023(2)o(5)
0.0500{5)o(6)0.l le9(5)o(7)
0.r289(5)o(8)
0.2096(6)o{e)
0.084r(5)o(10)
0.0959(5)o ( rl )0.r076(5)o(12)
02249(5)o(r3)
0.0459(5)o(14)
0.0667(s)o(r5)
0.0969(5)o(16)
0.1950(5)o(r7)
0.u74(5)o(18)
0.1324(5)o(le)
0.1330(6)o(20)
0.2050(5)o(2r)
0.058e(5)o(22)
0.1490(6)o(23)
0.1493(5)o(24).
0.2178(6)o(2siT
0.2304{5)B"q.A(A1
0.500
0.2192(4)0.517r(s)0.000
0.014{4)0.l l6(6)0.490(l)0.8881(4)0.948(l)0.0r38(2)0.0165(3)0.2509(2)0.7449(2)o.7ol4(2)0.2930(2)0.0109(4)0.0005(7)0.4u8Q)
0.2510(3)0.'1678Q)
0.7269(2)0.3005(2)0.06s3(7)4.1389(7)0.0808(8)0.M2(l)4.036{2)0.4412(6)0.5963(7)0.3424<7)0.,1608(9)0.I 684(7)0.3968(7)0.r883(7)0.2s22(8)0.6438(6)0.8723(7)0.8r60(7)0.n26(8)0.6742{7)0.67&A
0.8816(7)0.6707(7)0.3476(7)0.3545(8)0.1461(7)oJ579/J)-0.0024(8)0.@o.4832(2)0.1206(3)
0.0@
0.250
0.2J0
0.250

0.385
0.471
0.076

0.17
0.271
o.2l
0.t%t
0.
0.

An-.empirical absorption-correction
was applied r
Atom labcled 6 F in Moore €r 4i. (198t)
according to the procedure already described in Staned
atom wre rsfined istroDicalv. AnistroDically refined arom re eiyfl in
Demartin et aI. (1992); the minimum transmission the fom of the intropic equivaleit disflmem fm*r
defined m:
Bq = 4BId Be,tyb2Se,zy& Be,t)+o46sb)B(
1,3)l
factor is 0.61. After averagingthe symmetry-relateddata(R,r.= 4.7Voon F), 5401,independent
reflections
wereobtained;of these,2846with / > 3o(I) wereusedfor the structurerefinemenr.
Scatteringfactorsfor neutralatomsand anomalousdispersion conections were taken from Cromer &Waber (1974) and Cromer (1.974),respectively.
Starting from the atomic positionsreportedin Moore
TABLE 3, CRYSTAL DATAFOR SIGISMTJNDITE
et al. (1981), the structurewas refined by full-matrix
single crystal
powder data
least-squares, by minimizing rh; function
Xw(F,-klFcD2. The multiplicitiesof X(2), X(3), anda(A)16.406(5)16.394(4)b (A)e.%s(3)Al sites did not show appreciabledifferencesfrom
e.e32(2)c (A)24.470(5)24.437(7)1.00,0.50 and 0.50, respectively,and were fixed at()"P
tos.z3(z)105.78(2)thesevalues during the subsequentcycles.Weights
I'(A')
3s43(2)3828n)
assignedto individual observationswere l/&(F),CRYSTAL SYSTEM: nonelinic
SpACE GROllp: C2Jc Z= 4
where o(d) = [o2(0 + gD2]v"lzF"Lp, o2(0 is rhe
standarddeviationfor eachreflectionas derivedfrom
Mesurcd reflections: 5?4? with 4 < 20 < 60 .
counting statistics,k (= 0.04) is a coefficient forlndependentobssryed reflestiom with 1 > 3c(I): 2546
improving the goodnessof fit, and Lp is the Lorentzpolarization
factor.For all thecalculations"
we usedthe
R = 0.066
Rp = 0.073
PersonalSDP StructureDeterminationPackage(Frenz
1988"1991).The final R andR_ indicesare0.066and
R= [:(Fo-klFcl/xFo]:
R? = [:v(Fo-klFol)2/SwFozl l,
0.073, respectively;these values can be favorablycomparedwith the bestresultsreportedin the literature

831

SIGISMUNDITE"A BA-RICH MEMBER OF TTIE ARROJADITEGROUPTABLE5. BoNDDrsrANcEs (A) erp eNcles f) FoR SIGISMUNDITE TABLE 5. - ontilued
N-rr{))!
xz
Al-O(10) x2

x2

M(lx)r0(2)b
M(1x)-o(8)cM(lxlo{11)dM(lxlo(12)e<M(lx)-O>

2.502(15)
2.163(15)2.3t4(r3)2.37N14)
2.34

M(2!o(3)M(2)-O(19)f
M(2)-o(20)s

2.063(6)2.088(7)M(2>o(21)
M(2)-o(24)s

2.rr't(6')<M(2)-O>

2.058(6)2.081(6)2.081

M(3!o(25)
M(3){(l)aM(3).qe)M(3)-o{r4r
M(3)-qler
M(3)-O(23)<M(3)€>

2.A42G'
2.186(7)2.128(6)2.01s(6)2.'l3(7)2.025(6)2.088x(r)-o(4)x(l).q7)x(l)o(8)x(l)-o(8)hx(llo{l5xx(l)-o(15)sx(r)-o(l6xx(llo(t6)s<x(l)-o>

2.264{rr)2.803(8)x(2)-o(10)x(2)-oo3)x(2!o(16)x(2!o(l?)x(2)"o(20)x(2)-o(21)xQ)-aQ4)
x(2).....o(r2)<x(2)-o>2.307(7)2.323(',7)
2.690/7)
2.652(7)2.404(8')
2.528(8)2 3e3(8)3.471(10)2.471

2.43/7)
2.195(8)2.2s3(7)2.e01(8)2.576{8)2.183(7)2.451

2.r02(6)2.106{6)2.r19(7)2.272(5)2.21X6)2.028|7)
2.141

M(6)4(r2ts
M(6)-ql8)
M(6)-o(24F<tv(6)-o>2.28r(6)2.254(6)2.r2s(6)2.0ee?)
2.or6{?
2.366(6)2.190

M(7)4(25)e
M(?).o(3)M(7)€(7)M(7)-o(16)sM(fa(20)gM(4-o(22)<M(7)-O>

2.m46)
2.386(D2.060(6)2.ts4\'t)2.128(6)2.027(8)2.160x3)-o(e) Y2
Y2

2.6i5(6)2.702(5\2.366{6)2.485(6)
2.542

x2
x2
x2

2.836(8)2.694(1|)
2.Y26{tS)
2.819

M(6)-o(25)eM(6)"0(2)b
M(6)-o(6)x(3)Fo(il)x(3Fo(l4r Y2
x(3)-o(l5r \2<x(3LO>
K4)'ql)x4)-o(3)x(4)o0er<K4IO>x(4xlo(l) x2
X(4xlo(3) x2
x{4x]-o,Q3) x2<X(4x).O>x(s)-o(u)x(sFo{r8)X5)4(21)x(5!o(22)<K5)'O>

x2
x2
x2
x2

P(1)-O(l)P0!o(2)P(l)o(3)P(l)o(4)<P(1)-O>

1.566(7)r.4e7(6)1.503(7)1.534(r2)1.525o(l)-P(1Io(2)o(rlP(1).o(3)ql)-P(1!o(4)o(2)-P(r)-o(3)o{2)-P(r)-o(4)o(3)-P0!o(4)108.9(4)I 10.0(4)l1l.e(5)114.0{4)107.0(5)105.1(5)P(2>o{5)P(z)-o(6)P(2)-O{7)P(2)-o(8)<P(2)-O>

r.54e(6)r.s26(6)1.s34(6)l.sos(8)1.529

o(5FP(2)-o(6)o(5FP(2)-O(7)o(5)-P(2)o(8)oi6!P(2).o(7)o(6!.P(2>c{8)o(7FP(2)4(8)loe.2(3)r02.2(3)l I 1.8(4)l l l.E(4)112.7(4',)
108.8(4)P(4!O(r3)P(4>o(14)P(4)-O{15)
P(4)-o(16)<P(4)-O>

1.552(6)1.532(6)1.510(7)t.52r(7\ql3)-P(4)-O(14)o(13)-P(4!.O(r5)o{r3)-P(4}O(16)o{14)-P(4)-O(15)o(14)-P(4)-o(16)o( r5)-P(4)-o(l6)102.3(3)l l l,e(4)l0e.q(i)l l0.e(3)rtz.8(4)109.1(4)P(6)-0(21)P(6)0(22)P(6)O(23)P(6)-O(24)2.E35(10) <P(6)-0>
2.63400)
2.e4e0)2.806
2.846(6)2.733(6)2.90%6)2.77242.815

P(lxlo{l)POxlo(2)P(lx).o(3)Klxlo(4x)<P(I x)-O>

1.499(8)1.571(8)r.447(8)r.633(20)o(l)-P(lx)-o(2)o(l)-P(1x)-o(3)o(l)-P(lx)a(ax)o(2)-P(lx)-o(3)o(2!P(lxlo(ax)O(3)-P(lx)-o(4x)108.6(5)r7.2(5)109.5(8)l 12.9(5)105.l(7)102.8(8)P(3)Eo(e)P(3)-o(10)1.528(6)1.530(5)P(3)-OO2)<P(3)-O>

1.566(7)1.537o(e)-P(3)-o(10)o(e)-P(3)4(lr)o(e)-P(3)4(12)o(10)-P(3)4(ll)o(10)-P(3)-o(12)o(11).P(3)4(12)10e.7(3)loe.6(3)110.5(4)lll.6(3)107.4(3)lo8.o(3)P(5)-O(17)P(5),o{18)P(5)-O(r9)P(5!q20)<P(5!O>1.534(7)1.520(6)I 541(6)L53e(6)
1.534

o(rlP(s)-o(l8)o0n-P(s)-o(le)o(17)-P(5)-o(20)o(lE)-P(5)4(19)o(r8)-P(5)O(20)o(19)-P(s)€(20)

107.q3)110.8(4)108.5(3)lll.8(4)110.0(4)108.2(3)t <lt

P(3)-o0D

r.s22(6)1.53r(7)r.s27Q)
r.539(5)1.552(',7)'1.537b=x,l+y,z,a=-x.v.ll2-z:
e= ll2-x, lD+y, ll2-z;
d = x,i'-v, ll2+z:
p = riz-;. v-ln. u2-zi h= llz-x. ll2-\. l-2.

c=ln-x'312-y,l-z;
f = x' y-l' z:

replacementof K in the X(5) site by Ba and thepr;sence of cation vacanciesat the Na sites,the latter
requirements.
accountingfor charge-balance
The existenceof Ba-rich arrojaditehasbeenknown
for a long time. A sample from the Buranga mine,
Rwanda, contains 4.32 wt.To BaO, and another one
in Morocco,contains5.36wt.Ea
from Sidi-Bou-Kricha,
BaO (Moore & Ito 1979). More recently, Robinson
et al. (L992) describedtwo sarnplesof arrojaditefrom
Rapid Creek, Yukon Territory, having a BaO content
up to 7.00 wt.qo; consequently,the possibility ofexistenceof a new species,the barium analogue
However,in sigismundite,of anojadite,wassuggested.
a considerableamountof Mg alsois present,exceeding
the range of values so far reported for arrojadite dickinsonite(Moore&Ito I979,Robinsonet al. 1992),
DlscussIoN
andpartly replacingtransitionmetalsat the M [M(1) to
The structurerefinementof sigismunditeshowsthat M(7)l sites.The X(1) site is half-occupiedby Ca andthe major differenceswith respectto the otherminerals Sr, and X(5) containsBa and K. Since in anojaditeinsodiumof the arroiadite - dickinsonite series are the dickinsonite, which is considerablyricher

for the other structures of the arrojadite group.
Significant residualsof electron density in the finaldifferenceFouriersynthesist1.9(3)- 1.3(3)elA"l arelocated close to the X(5) and X(4) positions,andindicate the presence of disorder. Final atomic
coordinates are reported in Table 4, with bonddistancessn6 anglesin Table 5. Tables of atomic
displacement parameters and of observed andcalculated structure-factorsare available from the
Depository of UnpublishedData, CISTI, National
ResarchCouncil, Ottawa,Ontario, CanadaKIA 0S2.
The atomic amangementin two different planes atabouty - t/aandy = % is shownin Figures la and lb,
respectively.

THE CANADIAN

n
\a

t--e

MINERALOGISTSIGISMUNDITE.A BA-RICH MEMBER OF THE ARROJADITEGROT.IP

833

than sigismundite,Na occupiesthe sites X(2), X(3), distortedoctahedralcoordination.A slightly different
X(4), X(6), and X(7), a low occupancyof thesesites situationcanbe observedfor theM(7) site: in arrojadite
was expectedfor sigismunditealreadyon groundsof - dickinsonite,theM(7) coordinationpolyhedroncan
chemical analysis. The refinement of the crystal be either a squarepyramid or an octahedron(i.e.,
structurehas indeed shown that in sigismundite,only disorderedand partly occupied),with O(4x) included
rhe X(2) and X(3) sites are tully occupied by Na, in the coordination sphere.In sigismundite,M(7) is
whereasthe X(4) site is only partly occupied,and the always octahedrallycoordinated,with the O(3) atom,which is not disordered,occupyingthe sixth position'
X(6) andX(7) sitesare empty.
The refinement of the multiplicity of the Al site The overallmultiplicity of theM sitesis 5.18 (on theshows that no significant replacementby other basisofa Fe atomicscatteringfactor);the correspondelementsshould occur; this result is in complete ing resultfrom chemicalanalysisis 5.47.Becauseof
the uncertaintiesin the multiplicity and becauseweagreementwith resultsof the chemicalanalysis.
have modeledthe scatteringfactors to be of the same
shapeand proportionalto the numberof electrons,theDisorder of phosphategroups
acceptable.
resultis considered
Similar to arrojadite from Nickel Plate, South
Dakota (Moore et a!. l98l), one of the six non- TheX sites
equivalent POa grdups is disordered into two
The X sites [X(l) to X(7)] are occupiedby large
alternativeorientations,centeredon P(l) and P(lx),rangeof ionic radius.The
with a P(1)-P(1x)disunceof 0.882(7)A. The model cationswith a considerableof disorder statistically consistsof nvo face-sharing large values of the displacementparametersreflect
tetrahedrahaving the fourth vertex alternatively on the correspondingpositional disorder. This is the
oppositesides with respectto the sharedface. A reasonwhy the largestresidualsof electrondensityare
different situationwas observedby Moore et al. (1981) closeto thesesites.X(1) occurscloseto an inversion
in the structureof two other membersof the family, center and is separatedfrom its centrosymmetrical
where a common edge is shared between the two equivalentby 1.090(9)A; thusit can be at mosthalfto an
occupied.The geometryof this site corresponds
disorderedtetrahedra.
8-coordinatedpolyhedronwith X(l)-O distances
rangingfrom 2.183(7)to 2.901(8)A. The site
TheM sites
multiplicity (0.583) obtained by assuming the
The sevencationsitesM(l) to M(7) we essentially scatteringfactor of Ca for the atom in this position
occupied by Fe2+, Mg and Mn2*. The refined indicatesthat Ca is partly replacedby heaviercations.
multiplicity of these atomic positions (reported in If all Ca and almost all Sr determinedby chemical
Table 4) is basedon the scat[eringcurve of Fe. Unlike analysis are assignedto this site (Table 1), the+the membersof the arrojadite- dickinsoniteseries,the calculatedvalue of the site multiplicity 10.5(Ze,XcaquitepeculiarM(l) siteis split iqto two sitesM(l) and Zs,xs)lzca = 0.601 is in good agreementwith theM(lx), separatedby 0.81(1) A. The occupancyof refinedvalue.
The X(5)-O distances(Table5) areconsistentwith
the M(1x) position is correlated to the disordergroup.Wherethe M(lx)occupationofX(5) by Ba, K, Pb2+andSr. Na occupies
involvingthe P(l) phosphatesite is occupied,then the altemativeorientationof tfie the X(2) andX(3) sites,andthe X(4) sites(seebelow)
phosphategroup [with the P(lx) and O(4x) positions are only slightly populatedby Na. The X(6) andX(7)occupiedl should occur, otherwisean M(Lx)-O(4) sites of anojadite - dickinsoniteare vacant.Here, thedistanceof 1.18(2)A would result. A similar steric scatteringfactor of Na has been assumedfor X(2) to
X(4), andthat of Ba for X(5).
effect couples the occupancy of X(6) and M(l)In sigismundite,monovalentcations(e.9., K) arein arrojadite (Moore et al. 1981). In the present
extensivilyreplacedby divalentcations(Ba andPb2+),case, however,X(6) is vacant. As in anojadite dickinsonite,theM(2) polyhedronis a distortedsquare and hence the structureshould be deficient in somepyramid,andtheM(3),M(4), M(5) andM(6) siteshave cations in order to maintain charge balance. Thise
Hc. l. The crystal structureof sigismundite,as seenalong t0101:(a) part of the structureat about y = tA: (b) part of thestrucfureat abouty = Vz.Thelocationsof the largecationsIX(l) to X(5)l areindicatedby opencircles;the othermetalatoms
are at rhe centerof their coordinationpolyhedralM(l) to M(7)1,and the phosphorusatoms[P(l) to P(5)] are at the centerof the tetrahedra.

834

THE CANADIANMINERALOGISTF., cRAMAccioLl,C.M. & Preu, T. (1992): The
explainsthe low contentof Na in sigismundite,only DEMARTTN,
importanceof accuratecrystal sructure determinationof
about tbree-quartersof that found in most samples
uranium minerals.tr. Soddyite (UOr)r(SiO).2HrO. Actaof arrojadite. If some cations are omitted from the
Crystallogr.C48,1-4.
structureffor instance,asa consequence
ofprogressiveoxidation or leaching of the minerall, the order of FnsNz,
joint
B.A. (1988): Computen and crystallography:
cationomissionshouldbe X(6),X(7) = X(4) > X(5) >>progress.Comput.Phys.2, 4247.
X(3) (Moore et al. 1981,p. 1043).This predictionis
in good agreementwith what is observedhere, since(1991):lmprovedproductivitythroughcrystallothe X(6) andX(7) sitesarenot occupiedat all, andX(4)graphicpackages.CrystallographicComputing5. Oxford
UniversityPress,Oxford,U.K. (126-135).
is only sparselypopulated.This latter site is split iqto
two parrs [X(4) and X(4x), separatedby 1.00(5)A],daboth involved in steric hindranceproblemswith the Gunr,l, F. & OnraNor,P. (1987):Brevissimesegnalazioni
diverselocaliti mineralogicheitaliane. Riv. Mineral. Inl.
disorderedphosphategroup. These steric problems
1 , , 5 96- t .
are particularly evidentif one considersthe following
distances^:X@)-O(4x) = 0.74(2) A, x@x)-Ogi 1 JARosEwrcH,
E.J., Nei,rN, J,A., & NoRBERc,
J.A. (1980):
1.60(a)A; therefore,X(4) and X(4x) cannotboth be
Reference samples for electron microprobe analysis.
populated
ifP is at P(lx) andnotP(1).
GeostandardsNewsletter4, 43-47, 257-258.
ACKNoWLEDGEMENTS

MaNoentuo,J.A. ( I 98I ): The Gladstone-Dalerelationship.
IV. The compatibility conceptand its application. Caz.
Mineral.19.441450.

We aregratefulto Dr. P. Gentile,who collectedandprovided us with the sampleof sigismundite.We are
Menrno, S., MsLLs[, M. &ZsNsn, P.F.(1981):Srrucrurealso indebtedto Mr. I. Campostrinifor a preliminaryof arrojadite, KNaoCaMnnFe,0Al(POrr2(OH,F)r.
Acta
energy-dispersionanalysis of the mineral, to Dr. F.
Crystallogr.B37, 1733-1736.
Pezzottafor the microstructuralstudy of the sample,
and to Dr. S. Mulley for helpful discussion. MooRE, P.8., ARAKI, T., MERLINo,S., MELLNT,M. &Considerablehelp in revising the manuscript was
ZAN^zzJ,
P.F.(1981):The arrojadite- dickinsoniteseries
provided by the Editors and the Referees,among
KNaaCa@e,Mn)?iAl(OH)2@Orr2:crystal structffe andcrystalchemistry.Am. Mineral. 66, 1034-1049.
whom Drs. R.F. Matin and T.S. Erciq their usefulsuggestionsare gratefully acknowledged.
-

RnFERENcEs
BEDooG, F., MALR o, R., MoNTRAsto,
A. & ScrF,sA,
E.
(1995): I minerali della Provincia di Sondrio e della
Bregaglia grigionese. Val Bregaglia, Val Masino, Val
Coderae Valle Spluga.Bettini Press,Sondrio,Italy.

& Iro, J. (1979):Alluaudites,wyllieites,arrojadites:
crystal chemistry and nomenclature.Mineral. Mag. 43,
227-235.

RosD.{soN,
G.W., Ver VBlrsurzr,N,J., Arsnr, H.G. &STURMAN,
B.D. (1992): Mineralogy of the Rapid Creek
and Big Fish River are4 Yukon Territory. Mineral. Rec.
23. 1-47.

CRoMER,D.T. (1974): Intemational Tables for X-Ray Wtt-t-,G. (1979):POWLS:a powderleast-squares
program."I.
Crystallography4. Table 2.3.1. T'be Kynoch Press,
Appl. Crystallogr. 12, 483-485.
Birmingham,U.K. (presentdistributor:Kluwer Academic
Publishers,Dordrecht,The Netherlands).
& WesER,J.T. (1974):Intemntiornl Tablesfor
X-RayCrystallography
4.Table2.2.b.The KynochPress,
Birmingham,U.K. (presentdistributor: Kluwer Academic Received September 13, 1995, revised manuscript accepted
Publishers,Dordrecht.The Netherlands).
March28,1996.