American Mineralogist, Volume 65, pages 936-939, 1980
PeretaiteoCaSboOu(OH)r(SO 4)2. 2}I2O, a new mineral from Pereta, Tuscany, Italy
Snvro MENcHETTI
NIcoLA Crpnntt.
I stituto di Mineralogia dell' Universitd
Via La Pira 4, 50121 Firenze, Italy
Pnoro
Onr-eNot
Istituto di Mineralogia e Petrografia dell'Universitd
Via S. Maria 53, 56100 Pisa,Italy
AND CESARE SABELLI
CNR Centro di Studio per la Mineralogia e le Geochimica dei sedimenti
I stituto di Mineralo gia dell' Univ ersitd
Via La Pira 4, 50121 Firenze,Italy
Abstract
Peretaite,a new calcium and antimony sulfate mineral, occursas aggregatesof colorless
tabular crystalsin the antimony-bearingvein at Pereta,Tuscany,Italy. It is monoclinic, space
gtoupC2/c,with a: 24.641,
densityis
D : 5.598,c: 10.180A,
B:95.95". The calculated
4.06g cm-3. The cleavage{100} is perfect.Crystalsare alwaystwinned (100).Peretaiteis biaxial (+) with mean refractive index 1.841.The five strongestlines in the X-ray diffraction
3l l0.OO.
pattern are(d rn A, t, tttc4:12.191002oo;6.1221 400;3.1024 512;3.0667 8Cf/;2.451
On the basisof the wet-chemicalanalysis,the IR spectroscopy,the TGA spectrum,and espe'2H2Q.
cially the structuredetermination,the chemicalformula is CaSboO+(OH)r(SO4),
Introduction
In a paper dealing with a new find of klebelsbergite (Cipriani et al., 1980),some of us pointed out
that a new mineral is present among the accessory
minerals of the antimony-bearing vein at Pereta,
Tuscany, ttaly. Further study fully confirmed the
thesis.
The new species,CaSboOo(OH)r(SOo)r.2HrO,
is
named peretaite for the locality. Both the mineral
and the name have been approved by the Commission on New Minerals and Mineral Names, IMA.
Type specimensare depositedin the mineralogical
museumsof FlorenceUniversity (regionalcollection,
#164/l) and PisaUniversity.
Occurrence and paragenesis
columnar stibnite. Crystals of peretaite associated
with acicular crystalsof klebelsbergiteafe shown in
Figure l Other associatedminerals are stibnite,
qrrartz,calcite, pyrite, valentinite, kermesite,sulfur,
and gypsum. Aggregatesof klebelsbergitecrystals
and rarely of peretaite are often red from incrustations of valentinite. Unlike klebelsbergite,
which was found rather abundantly in the fissuresof
the stibnite veinlets, peretaite occurs closer to the
boundary with limestones.The mineral, as well as
klebelsbergite,has apparentlybeenformed by the action of sulfuric acid on stibnite; the sourceof the calcium in peretaiteis likely the limestoneof the countrv rock.
Chemistry
The environment where peretaite was found has
qualitative
Preliminary
analysesof peretaite were
been describedby Cipriani et al. (1980).Peretaiteoc- made with an oRTECX-ray microanalyzer and an
curs, in small quantities, as aggregatesof tabular ARL sEMe electron microprobe. However, since the
crystalsin the geodesof a deeply silicified limestone crystalsdecomposeunder the electronbeam, microfrom "Calcare Cavernoso,"and also in the cavitiesof probe resultswere considerednot reliable for a quanw3-wx/80/0910-0936$02.00
936
937
CIPRIANI ET AL.: PERETAITE
Table 2. X-ray powder diffraction-data for peretaite; d values are
inA
r/1o
dobs
dcalc
100 12.19 12.254
21
16
Table I
Chemical analysis of peretaite. All values are weight
percent
sb2o3
68. 31
69.09
6.58
6 .44
so3
18.78
17.62
Hzo
6.33
CaO
6.0
' l0 0 . 0 0
(1)
Tdo^l
(2) From
naro+:i
ana l vfi
31
110
11
9 1 0
2.0682.066
2.010
1'l
4.851
4.758
111
2.059 2.059
5
4.08
4.085
600
2.058
5
3.68
3.688
510
2
3.55
3.556
11
3.51
3.516
1.878 1.878
3
3.38
3.381
5
3.35
3.354
-602
312
820
11 1 0
-8
0 4
6 0 4
-2
2 4
1.817
0 2 4
1.858 1.859
8 0 4
11
511
I
10 0 0
4.-16
-5
k
2.449
4.85
16
h
2.451 2.451
400
-1
dcalc
1.860 -10 0 4
10 2 0
5
1.844 1.844
A
1.110 1.710 -14 0 2
3.31
3.316
3 . 10
3.098
3
1.699
'l
4
1.684 1.684 -11
't
.700
3 3 2
67
3.06
3.064
800
A
4
3.03
3.O29
602
2
1.668 1.668
4
2.967 2.968
710
1
1.609 1.609 -12 2 2
14
2.814 2.876
512
2
1.604 1.604
020
2
1 .582
12
2.799 2.799
'1
.582
-s
3 2
14 0 2
-5
1 6
3 1 6
13
2.727 2.129
220
2
1.556 1.556
5
2.696 2.698
o21
2
1.549 1.549
8 2 4
20
2.532 2.532
-204
6
1.532 1.532
16 0 0
1
1.511 1.5'tO -16 0 2
4
1.397 1.396
z-)31
004
17 1 0
to Ca, o,Sbo,rS'roO,uHr86on the basis of 16 oxygens,
or ideally CaSbi*O.(OH),(SO,), ' 2H,O from the
structural results and the infrared spectrum. Indeed,
both the structural determination and the IR spectroscopy gave clear indications, the first without any
doubt, on the presence ofsulfate groups as well as of
H-bonded water molecules and hydroxyl groups.
CrystallograPhy
(1)
Oxide
5 -451
200
deSs
4
24
titative determination, especially for sulfur. Therefore a wet-chemical analysis was perfoflned. About
20 mg of purified material was dissolved in I :5 HCI
and diluted to 25 ml with distilled water. Calcium
was determined by atomic absorption spectrometry,
using a Perkin Elmer 303 instrument. Antimony was
determined by alternating current anodic stripping
voltammetry, on hanging-drop mercury electrode in
lM HCl. Total sulfur was potentiometrically titrated
with Pb(ClOo), and an oRIoN 94-82lead ion electrode. The water content was inferred from a TGA
spectrum. The result, given in Table l, corresponds
5.45
6.121
I,/Io
s
't2
Fig. l. Crystals of peretaite associated with acicular crystals of
klebelsbergite; the largest crystal is 1.5 mm long (photo P. B.
Scortecci).
6.12
hkl
99.15
ta
ca l
results
X-ray single-crystal study (Weissenberg camera
and single-crystal diffractometer) indicated Laue
symmetry 2/m. Systematic extinctions are consistent
with the space groups A/c or Cc. The former, however, is the correct one from the structural study
(Menchetti and Sabelli, 1980b). All the examined
crystals appeared to be twinned with (100) as twin
plane.
The X-ray powder diffraction pattern (Table 2)
was obtained by means of a Philips diffractometer,
with CoKc radiation, NaF as internal standard, and
0.25o per min scanning speed. Indexing was per-
938
CIPRIANI ET AL.: PERETAITE
Fig. 2. Typical habit of a peretaite crystal.
formed on the basisof single-crystaldata and taking
into accountthe intensitiesof the reflectionscollected
for the structural study. In the powder pattern there
is a systematicenhancementof the intensitiesof ft00
reflectionsbecauseof a preferential orientation due
to the {100} cleavage.The unit-cell parameters,determined from powder data by means of leastsquarescalculations,are;a:24.641(2\, b : 5.598(2),
c : 10.180(l)A,
F : 95.95(l)'.',
Peretaitecrystalsappearflattened(100) and sometimes elongated[001].Two typical habits of peretaite
are shown in Figures 2 and 3. The observedforms
are {100}, [310], fl10] , {r22}, {00U, {010}, QrO],
{20U, {302}, and {601}. The largestcrystalshave
dimensionsup to 5 x 2 x 0.5 mm.
indentation hardness(VHN) with a l5-g load is between 170and 190kg mm-'.
Crystals are optically biaxial positive (+) with a
very large axial angle. The value of 2Ea measured
with a universalstage,usinghemisphereswith refraction index of 1.649,is nearly 102". The optical plane
is parallel to (010). By the prism method [(100) n
(310)la first index of refractionof 1.841(l)was measured. The correspondingvibration direction makes
an angleof about 28" with the 6 axis.A secondindex
of 1.935(1)wasmeasuredfor a vibrationdirectionalmost parallel to c. The mean index of refraction calculated from the Gladstone-Dalerelationship,using
the ideal chemical formula, the calculated density,
and the constants given by Mandarino (1976), is
1.841.
The TGA spectrum (taken under nitrogen atmosphere)showsa weight lossof about 67o,which is attributed to a dehydration reaction including both
HrO and OH. The tracing is not very sharp;however,
it seemspossibleto identify two successivestepsin
the temperaturerange 2W-240"C. This temperature
is about 60-70'C lower than that found for the corresponding effect in klebelsbergite.In the latter, however, only OH groups are present.
Physicalproperties
Crystalsof peretaiteare transparentand colorless,
with vitreous luster and [l00] cleavage.A density
>3.8 g cm-' was determined by the heavy-liquid
method; crystalsseemto float in Clerici solution with
a density of about 4.0 g cm-3.The calculateddensity
(for the ideal formula) is 4.06 g cm-'. The microI Lattice parametersusedin the crystal structuredetermination
are those measuredwith a single-crystaldiffractometer.They are
a : 24.66s(4),
6 : 5.6006(9),
c : 10.185(l)A,F : 9s.98(l)'.
Fig. 3. Another frequentlyencounteredcrystalhabit. Sometimes
the fqrm {001) is lacking.
CIPRIANI ET AL.: PERETAITE
WAVELENGTH
(PM)
N
z
o
o
2
=
o
z
E
F
2000
1800
1600
1400
1200
1000
FREAUENCY (CM-1)
Fig. 4. Infrared absorption spectrum ofperetait€.
The infrared spectrumwas obtainedfrom a potas- inversion center in the structure of peretaite and to
sium bromide disc containing peretaite. The pellet more strict selectionrules.
was heatedat l20oC for two hours. The spectrum,
taken from 4000 to 400 cm-', is shown in Figure 4.
Acknowledgments
The sharp absorptionat 3310cm-' due to the O-H
We thank the sAMIN SpA Company (F. Principato) for samstretching mode supports the presenceof hydroxyl pling permission,G. Sbrana and V. Schettinofor obtaining and
groups, with H-bonds strongerthan that of klebels- interpreting the infrared spectrum,and A. Bencini, P. Cellini Lebergite,which has the samepeak at 3435cm-'. The gittimo, and G. Piccardi for the chemicalanalysis.
occurrenceofa very broad band, ranging from 3500
References
to 2500 cm-' with a maximum at about 3000 cm-',
and of a weak band at 1640cm-', indicatesthe pres- Cipriani, N., S. Menchetti and C. Sabelli (1980) Klebelsbergite
and another antimony mineral from Pereta, Tuscany, Italy.
ence of water of hydration with strong H-bonds. In
NeuesJahrb. Mineral. Monatsh..223-229.
klebelsbergitethe correspondingpeaksare absent:in
Mandarino, J. A. (1976)The Gladstone-Dale relationship-Pan
the structureof this mineral there are no water moleI. Derivation of new constanrs.Can. Mineral., 14, 498-502.
cules (Menchetti and Sabelli, 1980a).Of the SOI- Menchetti, S. and C. Sabelli (1980a)The crystal structureof klestretchingvibrations, v., vr, and rr4were observed,at
belsbcrgite,Sb4O4(OH)2SOa.Am. Mineral., 65,931-935.
( 1980b) pereraite, CaSb+Oa(OH)z
and _
frequencies slightly different from klebelsbergite.
(SOa)2.2H2O:
its
atomic
arrangementand twinning. Am. MinThe presenceof z, (at 975 cm-') showsthat the suleral., 65,940-946.
fate tetrahedronis distorted.In addition rrrappearsas
a single peak and z, showsfewer structuresthan in
Manuscript received, April 2, 1980;
klebelsbergite:this may be due to the presenceof the
acceptedfor publication, April 22, 1980.