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TIIE
AMERICAN
MINERALOGIST,
PABSTITE,I THE TIN
VOL. 50, SEPTEMBER,
ANALOGUE
1965
OF BENITOITE
EucaNp B. Gnoss, California Diaision of Mines and. Geology, Son
Froncisco, California; JouN E. N. WarNwnrcrrr AND BBnN-q.noW.
Ev.tNS, Department of Geologyand.Geophysics,University of
Calif ornia, Berkeley,Calif ornia.
Alsrnacr
Pabstite is a new barium tin titanium siiicate found in recrystallized siliceous limestone
'I'he
from a quarry at Santa Cruz, California.
mineral occurs in small fractures and as
scattered grains in association n'ith quartz, calcite, tremolite, witherite, phlogopite, diop'fhe
side, forsterite and taramellite.
tin bearing minerals cassiterite,franckeite and stannite
are present locally. Pabstite is found as small anhedral, colorlessto white grains with a pink
tinge on a fresh surface, and appears rarely in crystal form showing a trigonal outline. The
mineral fluorescesbluish white in short-wave ultraviolet light.
Pabstite is uniaxial (-) and has abnormal interference colors Refractive indices are
o: 1.685, e: | 671. The measured specific gravity is 4.03 g/cm3, and calculated density is
407 g/cn3 Sinqle-crystal investigations confirm the presenceof the symmetry elements of
spacegroup P6:2, the same as that of benitoite. The dimensionsof the unit cellare o:6.706
+0.002, c:9 829+0.002 A. Its composition, determined by electron-probe microanalysis,
is Ba(Snn zz'Iio:a)SLOg.
The mineral is named for Professor A. Pabst of the Department of Geology and Geophysics, Universitl' of California, Berkeley.
INrnooucttoN ANDAcr<NowloncMENTS
Pabstite, the barium tin titanium silicate, was discoveredin 1963 by
Gail Dunning and JosephCooper,mineral collectors,at the PacificLimestone Products Quarry in Santa Cruz, California. Pabstite-bearingmaterial was submitted to the California Division of Mines and Geologyfor
identification. X-ray powder photographs of the mineral were very
similar to those of benitoite, with only slight changesin line spacings.A
proceduresshowed
qualitative examination by emission-spectrographic
the presenceof considerabletin, which could account for the refractive
indicesthat are lower than thosefor benitoite.
The authors gratefuliy acknowledge the cooperation of Messrs.
Dunning and Cooper who generously supplied most of the material
studied. The criticisms and suggestionsof various membersof the California Division of Mines and Geologlrare also appreciated.The microprobe anal]-siswas made possiblethrough funds provided by the National ScienceFoundation.
The mineral was named for Dr. A. Pabst, Professorof n'fineralogyat
the Universit;- of California,Berkele-v-;
his contributions to mineralogy
in general,zrndspecificallyto that of California, are widelv known. The
1 Name approved b1, the IMA Commission on Ne'w Minerals and Mineral Names.
tt64
PABSTITIi
1165
name, pabstite, is designatedfor those compositionsin which Sn predominates over Ti.
OccunnBNcB
To date pabstite has been found only at the Santa Cruz locaiity; however, a benitoite containing a small amount of tin has been recovered
from a drill core of recrystallizedlimestonetaken at Rush Creek in eastern Fresno County, California. It is conceivablethat pabstite may also
Frc. 1. Pabstite (white) associatedwith tarameilite (black) and quartz (gray) taken
under short-wave ultraviolet light. X1.5. Photo by Dunning
be found at this locality. At Santa Cruz, pabstite occursboth as fracture
filling and as disseminatedgrains in recrystallized siliceouslimestone
which shows evidenceof contact metamorphism. It is associzrted
with
calcite, qnartz, tremolite, witherite, phlogopite,diopside,minor amounts
of forsterite and taramellite. The tin-bearing suifosalts, stannite and
franckeite, and cassiteriteare dispersedthroughout the host limestone,
aithough only in minor amounts.
Pnysrcel AND OprrcAL PRopERTTES
Pabstite usually occurs as anhedral grains that are colorlessto white,
with a pink tinge when freshly broken. Most specimenswere recognized
in the field by fluorescenceunder ultraviolet light. Grains are commonly
1166
Z. B. GNOSS,J. D. N. WAINWRIGIIT AND B. W. EVANS
Tasrt 1. Puvsrc.tr-eno Oprrc.a.r.
Propnnttrs or Plsstttn ,q.NoBnNrtortr
Pabstite
Composition
Crystal system
Optic sign
Refractive indices
Hardness
Ba(Sno zzTioz:)SLOg
Hexagonal
Uniaxial (-)
o:1 .685
e:1.674
6
BaTiSi:Oe
Hexagonal
Uniaxial (*)
a : | . 75 7 1
e:1.8041
o
I Louderback, 1909.
lessthan 2 mm in diameter and aggregatesdo not exceed10 mm (Fig. 1).
After acid etching of the enclosingcarbonaterock, a few crystals were
found with a trigonal outline. The grains are vitreous and usually include small rods of tremolite which make a clean separation of the mineral difficult. Hardnessis approximately 6 on Mohs' scale,and density is
4.03 g/cm3, determined on a modified Roller-Smith balance. The measured density agreeswell with the calculatedfigure of 4.07 g/ cms.
The mineral is uniaxial (-), showingstrong anomalousblue-violetand
golden-yeliow interference colors. Refractive indices determined with
s o d i u m - v a p o rl i g h t a r e @ : 1 . 6 8 5 + 0 . 0 0 2 a n d e: 1 . 6 7 4 + 0 . 0 0 2 , w i t h l o w
birefringence; dichroism absent. Most of the grains contain minute
bubble and solid inclusions. Known physical and optical properties and
chemical composition of this material are listed in Table 1, with the
correspondingdata for benitoite added for comparison.The optics suggest that at some compositionthe material is isotropic.
CuBlrrsrnv
Pabstite from Santa Cruz has been analyzedwith an A.R.L. electronprobe microanalyzer(Table 2). No elementspossessingatomic numbers
greater than 10 (other than those listed) were detected by the microTllrln
2. AN,e.r,vsrsor Paesrrrn lnolr Serra Cnuz
wt.7a
SiOz
Tio:
SnOz
BaO
Total
3.8
24.4
33.2
99.r
1167
PABSTITE
probe; detection limits are O.0t7o for most elements,but rise from this
value to 0.1/6lrom Si(14) to Na(11). Some antipathetic variation of Ti
and Sn was found from point to point, amounting to approximately
+057a TiOz and t10/6 SnO2.SiKo, TiKa, and BaLB2lines were standardizedwith natural benitoite,which was consideredaspure BaTiSirOg,
an assumption that appearsreasonablejudging from the analvsesof Blasdale (Louderback, 1909). Cassiteritefree from Fe, Mn, W, and Ta impurities was used for the Sn determination. Correctionswere made for
background, r-ray absorption, and atomic number (using tables prepared by I. Adler), exceptin the caseof Sn. Becauseof the large difference
in mean atomic number betweenpabstite (30) and cassiterite(41), it was
Tasrn 3. Cnr,r, Darl
lon Bnlqrtottn,
Benitoite
o (A)
d (A)
Volume of cel (43)
Cell content
Measured density
Calculated density
Space group
Panstrr,
aNo BaSnSi:Og
Pabstite
6 6410+0.0007 6 . 7 0 6 + 0 . 0 0 2
9 . 7 5 9 7 + 0 . 0 0 1 0 9 .829+0.002
382.76
372.77
Ti)SLOe]
2(BaTiSlOs) 2[Ba(Sn,
3 .65 g/cm3
3 68 g/cm3
P6c2
4.03 g/cma
4.07 g/cmg
P6c2
BaSnSLOg
6.724+0.002
9.854+0.002
385.83
2(BaSnSfuOs)
4.17 g/cmg
preferred for the Sn determination to use tables by Colby and Niedermeyer (1964) for absorption and an expressionfor the atomic number
correctionby Reed and Long (unpublished).
On the basis of nine oxygens, the analysis in Table 2 canbe recast to
which clearly shows the analogy with benitoite,
Bar orSno.zzTi6.23Si2.eeOe,
may be applied
BaTiSiaOg.Thus, an ideal formula of Iia(Sno.z7Ti0.ze)SLOe
to the titanian pabstite from Santa Cruz.
D e s p i t e t h e c l o s es i m i l a r i t i e si n c h a r g ea n d i o n i c s i z e ( S n a + : 0 . 71 h ,
1ia+:0.68 A), appreciablesubstitution of Sn for Ti seemsto have been
recordedrarely. Ramdohr (1936) describeda variety of sphenecontaining at least 10/6 Sn from Arandis, S. W. Africa. SnOzin benitoite from
Fresno County, California was found with the electron probe to range
from zero to 4.1/6, that is, up to ll. /e substitution of pabstite for
benitoite. The benitoite of the type locality is completely free of Sn.
Pure barium tin silicate has been synthesizedfrom a mixture of stoichiometric composition in a simple hydrothermal apparatus at 330oC. and
saturated-water-vaporpressure.Large crystals of sanbornite, BaSizOs,
were
were producedat the sametimelhowever, the crystalsof BaSnSiaOs
1168
E. B, GROSS,J. E. N, WAINWRIGHT AND B. W. EI.ANS
Tenr,n 4. CouperrsoN ol OtsBnvpn Powoon LrNns. CuKa Rllu.rror,l
hkl
100
002
lo2
110
111
200
r72
202
004
104
2t0
211
212
114
300
20+
213
302
220
006\
2r4l
310
qrr)
,tlc \
Pabstite
dAmeas.
Iobs.
5 829
4.910
3.762
3 .363
3.181
2.912
2 775
2 505
2.465
2 267
2.204
2.t31
2 0t2
1 987
1.941
1. 8 8 1
1 .807
t.682
r.643
30
l.)
100
30
10
18
90
3
5
l.)
5
faint
20
IJ
l.)
lt
7
l.)
3o4J
116
s.848
4.933
3.770
3 370
3.192
2.917
2.784
2.512
2.465
2.273
2.206
2.132
2.014
1.989
1.950
1 883
1.857
1.811
1.682
35
20
100
50
15
20
90
8
22
7
t7
10
8
30
20
20
very faint
22
12
r.&3
20
1.614 very faint
1.591
15
not resolved
1o6J
3 12\
BaSnSi3Oe
dAmeas.
Iobs
1.535
13
not resolved
1.476
15
5
18
1. 5 8 1
1. 5 3 9
1.527
1.477
Benitoite
dAmeas.
Iobs.
s 750
4.880
3.723
s.326
3.148
2.875
2.747
2.481
2.436
2.2+3
2.175
2.122
|.987
1.966
|.9t6
1.860
1.807
1.784
r.662
1.622
30
7
100
25
20
35
90
13
18
15
25
15
20
25
15
t7
3
20
10
20
1 598
very faint
| 574
20
not resolved
10
IJ
l.)
20
1.518
20
not resolved
1.460
20
not of a size suitable for single-crystal examination. synthesis was also
successfullycarried out at 500' C. and 15,000psil again,sanbornitewas
present.No other phasesappearedto be present.
X-nay CnvsrarrocRApgy
X-ray diffraction patterns of pabstite are very similar to those of
benitoite, but relatively minor changes in the intensity of certain lines
and small changes in spacings were observed in powder photographs.
Examination of single-crystal photographs taken with both the Weissenberg and precession devices confirm the similarity; at the same time,
those spectra most affected by the substitution of Sn for Ti are clearlv
discernible.
The spacegroup for pabstite has been deduced as p6c2, the same as
PABSTITE
1169
that of benitoite. The pertinent crystallographic data for benitoite,
pabstite, and synthetic BaSnSirOgare listed in Table 3. Cell dimensions
for pabstite and benitoite were determined from single-crystalobservations, those of BaSnSirOgfrom powder lines in which the Ka components were resolved.The refined data for benitoite are from Fischer
(1964).A comparisonof observedpowderlinesfor benitoite,pabstite, and
BaSnSirOgis presentedin Table 4. Line intensities were estimated by
visual comparison with a film of scaleddensities.
RnlnneNcBs
(1964) Absorption correction tables for microprobe
Cor-rv, J. W. ,qsl J. Ir. Nroornuovur
analysis. USAEC Report NLCO-914.
Frscnnn, K. F. (1964) Personal communication.
Lountnr.tcr,
G. D. (1909). Benitoite, its paragenesis and mode of occtrrence. Univ.
Cal,iJ.P ubl..Geol..5, 23, 331-380.
RATDoHR, Paul (1936) Ein Zinnvorkommen im Marmor bei Arandis, Deutsch-Siidwestafrika. Neues f ahrbuch Mineral,.70, Abt. A, 1-48.
Resn, D. E. ,qNo Rusruu Rov (1955) On the stability and hydrothermal synthesis of
benitoite. A ln. M iner al. 4o, 542-SM.
Zacnrr:asnN, W. H. (1930) The structure of benitoite. Zei.t. Kri.st.74,139-746.
Manuscr,iptreceired, f anmly7,
1965; accepted,Jorpubl,i'cation,February 9, 1965.