Mineralogical Magazine, December 2012, Vol. 76(7), pp. 2773 2783

D’ansite-(Mn), Na21Mn2+(SO4)10Cl3 and d’ansite-(Fe),Na21Fe2+(SO4)10Cl3, two new minerals from volcanic
fumaroles
F. DEMARTIN1,*, I. CAMPOSTRINI1, C. CASTELLANO1, C. M. GRAMACCIOLI1 AND M. RUSSO2
1
2

Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy
Istituto Nazionale di Geofisica e Vulcanologia, Sez. Napoli ! Osservatorio Vesuviano, via Diocleziano 328,
80124 Napoli, Italy[Received 2 July 2012; Accepted 12 October 2012; Associate Editor: Stuart Mills]
ABSTRACTThe new minerals d’ansite (Mn), Na21Mn2+(SO4)10Cl3, and d’ansite (Fe), Na21Fe2+(SO4)10Cl3, occur
as encrustations in fumaroles at Vesuvius, Naples, Italy and La Fossa crater, Vulcano, Aeolian Islands,
Italy, respectively. Both minerals are cubic and crystallize in space group I4̄3d. D’ansite (Mn) forms
colourless translucent tristetrahedral crystals up to 0.2 mm on edge; d’ansite (Fe) forms aggregates ofcolourless to white complex isometric crystals of about the same size. Chemical analyses obtained byenergy dispersive spectrometry on an electron microprobe gave the following mean compositions:d’ansite (Mn), Na2O 39.37, MnO 3.46, MgO 0.13, SO3 49.99, Cl 6.36, O Cl !1.44, total 97.87 wt.%,
corresponding to an empirical formula, on the basis of 43 anions, ofNa20.61(Mn2+
0.79Mg0.05)S0.84S10.13O40.09Cl2.91; and d’ansite (Fe), Na2O 39.12, FeO 4.18, MgO 0.12,
SO3 49.91, Cl 6.81, O Cl !1.54, total 98.60 wt.%, corresponding to an empirical formula ofNa20.42(Fe2+0.94 Mg0.05)S0.99S10.08O 39.89Cl3.11. The six strongest reflections in the X ray powder
diffraction pattern of d’ansite (Fe) [listed as dobs(Å) (I) (hkl)] are as follows: 2.807(100)(044),
2.570(37)(235), 1.714(29)(129), 3.384(27)(233), 3.113(26)(134), 2.108(15)(237). The unit cellparameters obtained from single crystal data are 15.9291(9) and 15.882(3) Å for d’ansite (Mn) andd’ansite (Fe), respectively. The structure of both minerals was refined, using single crystal diffraction
data, to final R parameters of 0.0309 and 0.0336 on reflections with I > 2s(I). The structure contains
three independent Na sites, one of which is partially occupied by Mn2+ or Fe2+, two independent sulfate
anions and one chlorine site.
K EY WORDS : d’ansite (Mn), d’ansite (Fe), new mineral species, crystal structure, sublimates, fumaroles,
Vulcano Island, Vesuvius, Italy.

Introduction
D’ANSITE, Na21Mg(SO4)10Cl3, was first describedin 1909 by R. Görgey from evaporite deposits
near Innsbruck in the Tyrol region, Austria, but it
was not named or studied mineralogically until
Autenrieth and Braune (1958) produced crystals
in their studies of the system* E mail: francesco.demartin@unimi.it
DOI: 10.1180/minmag.2012.076.7.10# 2012 The Mineralogical Society!
Na +!Mg2+ !SO2!
4 !Cl !H 2 O. Strunz (1958)
determined the structure of synthetic material
produced by these authors and reported that themineral crystallized in space group I4̄3m. Burzlaff
and Hellner (1961) synthesized several analogous
phases containing a number of different cations inplace of Mg2+, including Ni2+, Co2+, Fe2+, Mn2+,
Cd2+ and Zn2+, and determined the structure of‘Zn d’ansite’, also in space group I4̄3d.
In 1972, d’ansite was found to be widelydistributed in a Palaeogene salt deposit in Central
China (Yihua et al., 1975). The structure wasF. DEMARTIN ET AL.

FIG. 1. A backscattered electron image of a tristetrahedral crystal of d’ansite (Mn) with aphthitalite from Vesuvius,
Naples, Italy.

solved in space group I4̄32, but the agreement
index, R, of ~15% was poor. The structure of ‘Znd’ansite’ was reconsidered by Burzlaff and Grube(1980) who noted that the crystals of this
synthetic phase were invariably twinned andproposed a lower symmetry. On the basis of the
optical properties and the anomalous displace
ment parameters for the atoms on the threefold
axis, R3c or Cc were reported as possible spacegroups. Fifteen years later, Lange and Burzlaff(1995) applied the Laue diffractometer techniqueto a crystal of ‘Zn d’ansite’, and refined its
structure in space group I4̄3d.
In the course of our studies of fumarole
minerals, which have already resulted in the
discovery of several new species (Demartin et al.,2010a,b, 2011; Campostrini et al., 2011), two newminerals related to d’ansite, containing Fe2+ andMn2+ in place of Mg2+, have been characterized
and named d’ansite (Fe) and d’ansite (Mn),respectively. The first of these minerals wascollected in 2008 in an intracrater fumarole witha temperature of about 300ºC at La Fossa Crater,
Vulcano Island [fumarole FA in Borodaev et al.
(2000) and Pinto et al. (2006)]; this mineral was
described in Campostrini et al. (2011) as
unknown species UKI fo29. The second of theseminerals was collected in May 1927 by A.
Malladra in a 1926 eruption fumarole with a2774

temperature of about 350ºC at Vesuvius, Naples.
Both minerals and their names have been
approved by the IMA Commission on New
Minerals, Nomenclature and Classification (IMA2011 065 and 2011 064). Holotype d’ansite (Mn)has been deposited in the mineral collections of
the Osservatorio Vesuviano, Naples (undercatalogue number OV128). The crystal fragmentused for the structure determination is housed in
the reference collection of the Dipartimento di

FIG. 2. Crystal drawing of d’ansite (Mn).

D’ANSITE (MN) AND D’ANSITE (FE), TWO NEW MINERALS

FIG. 3. Backscattered electron images of d’ansite (Fe) with adranosite from La Fossa Crater, Vulcano, Aeolian
Islands, Italy.

Chimica at the Università degli Studi di Milano(catalogue no. 2011 03) together with the typespecimen of d’ansite (Fe) (catalogue no. 201102). A description of the two new species isreported in the following text.

Occurrence, physical properties andchemical data
D’ansite (Mn) forms colourless translucent triste
trahedral crystals up to 0.2 mm on edge (Figs 1
and 2) associated with halite and aphthitalite. Its

FIG. 4. Backscattered electron images of d’ansite (Fe) with adranosite from La Fossa Crater, Vulcano, Aeolian
Islands, Italy.

2775

F. DEMARTIN ET AL.

FIG. 5. Crystal drawing of d’ansite (Fe) (see the crystal
in Fig. 4, upper left, for comparison).

calculated density is 2.610 g cm!3 (from single
crystal X ray data and chemical composition). It
is optically isotropic with n
1.50(1) (at awavelength of 589 nm, determined by immersion
in benzene!monochlorobenzene). The compat

ibility index, [1 ! (Kp/Kc)], is 0.001, which issuperior according to Mandarino (1981).
D’ansite (Fe) occurs as aggregates of colour
less to white complex isometric crystals up to
0.2 mm in size (Figs 3!5) on a pyroclastic
breccia, associated with sassolite, adranosite andas yet uncharacterized sulfate chlorides, which
are currently under investigation. Its measured
density is 2.62(1) g cm!3 (determined by flotationin tribromomethane!trichloromethane); and its
calculated density is 2.644 g cm!3 (on the basis ofsingle crystal X ray data and chemical composition). It is optically isotropic with n 1.51(1) (at awavelength of 589 nm, determined by immersion
in benzene!monochlorobenzene). The compat
ibility index, [1 ! (Kp/Kc)], is !0.005, which issuperior according to Mandarino (1981).
Both minerals have a white streak and avitreous lustre, and neither is fluorescent when
exposed to either LW or SW ultraviolet radiation.
Their hardness was not determined, their tenacity
is brittle and no cleavage is evident.
Chemical analyses of both minerals werecarried out on a JEOL JSM 5500LV electron
microscope equipped with an energy dispersive
spectrometer operating at 20 kV, 10 pA with a

TABLE 1. Analytical data for d’ansite (Mn) and d’ansite (Fe).
Constituent

Mean (wt.%)

Range

SD

Probe standard

D’ansite (Mn)*
Na2O
MnO
MgO
SO3
Cl
O=Cl
Total

39.37
3.46
0.13
49.99
6.36
!1.44
97.87

38.47!40.20
3.38!3.62
0.06!0.18
49.22!50.68
6.20!6.63

0.52
0.22
0.16
0.35
0.24

AlbiteAlmandine spessartine
Almandine spessartine
Adranosite
Adranosite

D’ansite (Fe)**
Na2O
FeO
MgO
SO3
Cl
O=Cl
Total

39.12
4.18
0.12
49.91
6.81
!1.54
98.60

38.49!41.05
3.91!4.35
0.07!0.18
49.56!51.68
6.28!7.42

0.53
0.25
0.13
0.36
0.24

AlbiteAlmandine garnet
Almandine garnet
Adranosite
Adranosite* The mean values based on 6 analyses. The empirical formula derived from chemical analysis on the basis of 43
2+anions p.f.u. is Na20.61(Mn2+
0.79Mg0.05)S0.84S10.13O40.09Cl2.91. The simplified formula is Na21Mn (SO4)10Cl3.
** The mean values based on 8 analyses. The empirical formula derived from chemical analysis on the basis of 43
2+anions p.f.u. is Na20.42(Fe2+
0.94Mg0.05)S0.99S10.08O39.89Cl3.11. The simplified formula is Na21Fe (SO4)10Cl3.

2776

D’ANSITE (MN) AND D’ANSITE (FE), TWO NEW MINERALS

2 mm beam diameter. The analytical results arereported in Table 1. The elemental concentrations
were determined using the Ka lines of Na, Mg,
Mn, Fe, Cl and S. The empirical formula (on thebasis of 43 anions) derived from the chemical
analysis of d’ansite (Mn) is
Na20.61(Mn2+
0.79Mg0.05)S0.84S10.13O40.09Cl2.91; thatof d’ansite (Fe) is Na20.42(Fe2+0.94 Mg 0.05 ) S0.99
S10.08O39.89Cl3.11. The corresponding simplified
form ul ae ar e N a 2 1 M n 2 + (SO 4 ) 1 0 Cl 3 andNa21Fe2+(SO4)10Cl3, respectively.

X-ray data
The X ray powder diffraction data for d’ansite(Fe) were collected using a Rigaku D MAXII
diffractometer with CuKa radiation (Table 2).
The unit cell parameter a
15.8842(7) Å was
obtained from a least squares refinement using the
program UNITCELL (Holland and Redfern,1997). The powder pattern of d’ansite (Mn)
could not be measured due to the extreme scarcity
of material and the pattern calculated from single
crystal X ray data is reported in Table 2 instead.

TABLE 2. X ray powder diffraction data for d’ansite (Mn) and d’ansite (Fe).

h k l
1 1 2
0 2 2
0 1 3
1 2 3
0 0 4
0 2 4
2 3 3
2 2 4
1 3 4
1 2 5
0 4 4
0 3 5
2 3 5
0 2 6
1 4 5
1 3 6
4 4 4
3 4 5
1 2 7
2 4 6
0 3 7
2 3 7
0 0 8
0 2 8
3 5 6
2 2 8
1 3 8
2 5 7
0 1 9
1 2 9
4 6 6
1 5 8
3 6 7
4 4 8
1 1 10D’ansite (Mn)
(I/Io)calc*
10
1
3
30
35
12
95
3
45
15
100
3
38
25
8
5
8
10
18
2
1
16
3
2
17
2
9
2
3
25
4
2
6
4
3

dcalc (Å)*(I/Io)obs

6.503
5.632
5.037
4.257
3.982
3.562
3.396
3.252
3.124
2.908
2.816
2.732
2.584
2.519
2.458
2.349
2.299
2.253
2.168
2.129
2.092
2.023
1.991
1.932
1.904
1.877
1.852
1.804
1.759
1.718
1.698
1.679
1.643
1.626
1.577

7
1
3
6
4
2
27
8
26
14
100
37
12
5
3
1
4
15
2
2
15
2
14
9

29
2
4
3
3

D’ansite (Fe)(I/Io)calc*
dobs (Å)
10
1
3
31
35
12
96
2
43
16
100
3
36
25
11
5
6
9
16
2
2
14
6
2
15
2
7
2
3
25
4
2
5
4
2

dcalc (Å)**

6.499
5.586
5.055
4.239
3.969
3.545
3.384
3.216
3.113
2.900
2.807

6.485
5.616
5.023
4.245
3.971
3.552
3.387
3.243
3.116
2.900
2.808

2.570
2.514
2.451
2.337
2.298
2.246
2.161
2.133
2.083
2.018

2.577
2.512
2.451
2.342
2.293
2.246
2.162
2.123
2.086
2.017

1.927
1.899
1.875

1.926
1.899
1.872

1.714

1.713

1.676
1.632
1.623
1.574

1.674
1.638
1.621
1.573

* Calculated from the refined structure.
** Calculated from a = 15.8842(7) Å, obtained from least squares refinement of the observed data using the program
UNITCELL (Holland and Redfern, 1997).

2777

F. DEMARTIN ET AL.

TABLE 3. Crystal data and structure refinement details for d’ansite (Mn) and d’ansite (Fe).
D’ansite (Mn)D’ansite (Fe)Weighting scheme

Na21.48Fe0.52(SO4)10Cl3
Na21.49Mn0.51(SO4)10Cl3
cubic
cubic
I43d
I43d
15.9291(9)15.882(3)4041.8(4)4006(1)
4
4
2.611
2.644
0.71073
0.71073
1.256
1.287
0.920, 1.000
0.883, 1.000
0.0760.0760.07
0.0360.0360.03
0.99!34.05
1.00!24.21!24 4 h 4 24, !24 4 k 4 24, !184 h 4 18, !18 4 k 4 18,!24 4 l 4 24
!18 4 l 4 18
23,904
11,394
1366, 0.035
540, 0.16
1287
407
Full matrix least squares on F2
Full matrix least squares on F2
0.03090.03360.08220.05481.061
0.925
w = 1/[s2(Fo2) + (0.0469q)2 +w = 1/[s2(Fo2) + (0.0201q)2]
5.803q]

Min and max electron density
residual (e Å!3)!3.86, 4.80

FormulaCrystal system
Space groupa (Å)
V (Å3)Z
Dcalc (g cm!3)
Wavelength (Å)
m (mm!1)
Min/max transmission factors
Crystal size (mm)y range for data collection (º)
Index ranges
Measured reflections
Unique reflections, Rint
Observed reflections [I > 2s(I)]Refinement methods
R [observed reflections]wR2 [all data]
S (goodness of fit on F2 )!0.27, 0.32

Refinement parameters are: R = S||Fo| ! |Fc||/S|Fo|; wR2 = {S[w(Fo2 ! Fc2)2]/S[w(Fo2)2]}!;q = [max(0, Fo2) + 2Fc2]/3; S = {S[w(Fo2 ! Fc2)]/(n ! p)}! , where n is the number of reflections and p is thenumber of refined parameters.

The unit cell parameters obtained for bothminerals from single crystal reflections with I >2s(I) are reported in Table 3, together with otherdetails concerning data collection and refinement.
The diffraction intensities were collected using a
Bruker Apex II diffractometer equipped with a 2K
CCD detector and MoKa radiation (l0.71073 Å); a one minute frame time and 0.5ºframe width were used. Intensity data werereduced using the program SAINT (Bruker,
2001), and corrected for Lorentz, polarization
and background effects. An absorption correction
was applied using the SADABS program(Sheldrick, 2000). Taking the debate on thespace group of d’ansite, outlined in the foregoing
text, into account, and having checked that no
violations of the extinction rules for the I4̄3d
space group were present, such a symmetry wasconsidered to be the most plausible and thestructure was solved ab initio by direct methods
2778

and refined using the SHELXL97 program(Sheldrick, 2008) implemented in the WinGX
suite of software (Farrugia, 1999). In agreementwith the indications of the chemical analysis andof the anisotropic displacement parameters,
during the refinement a partial replacement of
Na by Mn or Fe in Wyckoff site 16c was allowed
and the corresponding occupancies refined(Tables 4 and 5).
The chemical formula obtained from therefinement of d’ansite (Mn), Na 21.49 Mn 0.51
(SO4)10Cl3, is in good agreement with theformula calculated from the chemical analyses
and has 22.51 positive charges for the cation sum,compared to 23 negative charges for the anions.
Due to the similarity in the scattering factors of
Mg and Na, a structural model with the small
amount of Mg that was detected in the chemical
analysis was not refined, although such a model
might have improved the charge balance.

48e
24d
16c
24d
16c
48e
48e
48e
16c
12b

Wyckoffsite

0 88363(6)0 00000 07623(7)0 01843(4)0 96021(3)!0 0337(1)0 0727(1)0 9134(2)0 9078(2)0 0000x/az/c

0 37538(6)0 84843(6)0 25000 0442(1)0 57623(7)0 92377(7)0 50000 75000 46021(3)0 03979(3)0 4269(1)0 7295(1)0 5211(1)0 6784(1)0 4767(2) !0 0372(1)0 4078(2)0 0923(2)0 25000 8750y/b
0 0216(4)0 176(3)0 0356(6)0 0114(2)0 0150(1)0 0238(7)0 0340(9)0 068(2)0 085(2)0 0191(2)U11
0 0241(4)0 048(1)0 0356(6)0 0172(3)0 0150(1)0 0248(8)0 0305(9)0 045(1)0 085(2)0 0191(2)U22
0 0247(4)0 0154(7)0 356(6)0 0125(2)0 0150(1)0 0326(9)0 0320(9)0 031(1)0 085(2)0 0170(3)U33
0 0044(3)0!0 0039(4)0 0007(2)!0 0011(1)!0 0044(6)0 0066(7)!0 0081(9)0 030(2)
0

U23

U12

0 0034(3)0 0049(4)0!0 045(2)!0 0039(4)0 0039(4)00!0 0011(1)0 0011(1)!0 0035(6) !0 0077(6)0 0210(7)0 0011(7)!0 025(1)0 023(1)0 030(2) !0 030(2)
0
0

U13

2779

48e
24d
16c
24d
16c
48e
48e
48e
16c
12b

Na1
Na2
Na3/Fe
S1
S2
O1
O2
O3
O4
Cl

0 88098(4)0 00000 08027(4)0 01852(3)0 96103(3)!0 03390(6)0 07233(6)0 91376(8)0 90884(8)0 0000x/az/c

0 37440(4)0 84834(3)0 25000 04293(5)0 58027(4)0 91973(4)0 50000 75000 46103(3)0 03897(3)0 42636(6)0 73325(6)0 51656(6)0 67692(7)0 47536(7) !0 03641(7)0 40884(8)0 09116(8)0 25000 8750y/b
0 0236(3)0 152(1)0 0454(3)0 0102(2)0 0164(1)0 0194(5)0 0355(6)0 0887(9)0 1002(9)0 0244(2)U11
0 0239(3)0 0371(6)0 0454(3)0 0240(3)0 0164(1)0 0323(6)0 0312(7)0 0642(8)0 1002(9)0 0244(2)U22

0 0252(3)0 0180(5)0 0454(3)0 0172(3)0 0164(1)0 0305(6)0 0449(7)0 0259(6)0 1002(9)0 0136(4)

U33

U13

U12
0 0024(3)0 0017(3)0 0014(3)00!0 0320(7)!0 0027(3) !0 0027(3)0 0027(3)0 0034(3)00!0 0018(2) !0 0018(2)0 0018(2)0 0005(5)0 0027(5) !0 0101(6)0 0132(6)0 0243(6)0 0076(6)!0 0094(6) !0 0257(7)0 0365(7)0 0308(8)0 0308(8) !0 0308(8)
0
0
0

U23

Ueq

+

+

0 0243(2)0 0689(4)0 0454(3)0 0171(1)0 0164(1)0 0274(3)0 0372(4)0 0596(4)0 1002(9)0 0208(2)Refined occupancies for the Na3 site are Na = 0 870(1), Fe = 0 130(1) The anisotropic displacement factor exponent takes the form: !2p2(U11h2(a*)2 +2U12hka*b* + ) The value of Ueq = ˆ!¯(U11 + U22 + U33)

Wyckoffsite

Atom

TABLE 5. Atom coordinates and displacement parameters [Uij/Ueq] (Å2) for d’ansite-(Fe).

Ueq
0 0235(2)0 080(1)0 0356(6)0 0137(1)0 0150(1)0 0270(4)0 0322(4)0 0479(6)0 085(2)0 0184(2)Refined occupancies for the Na3 site are Na = 0 873(1), Mn = 0 127(1) The anisotropic displacement factor exponent takes the form: !2p2(U11h2(a*)2 +2U12hka*b* + ) The value of Ueq = ˆ!¯(U11 + U22 + U33)

Na1
Na2
Na3/Mn
S1
S2
O1
O2
O3
O4
Cl

Atom

TABLE 4. Atom coordinates and displacement parameters [Uij/Ueq ] (Å2) for d’ansite-(Mn).

D’ANSITE (MN) AND D’ANSITE (FE), TWO NEW MINERALS

F. DEMARTIN ET AL.

TABLE 6. Relevant interatomic distances (Å), angles (º) and bond valences (vu).
D’ansite (Mn)D’ansite (Fe)Na1!O1Na1!O1Na1!O2
Na1!O3
Na1!O3
Na1!Cl2.334(2)2.449(2)2.354(2)2.479(2)2.509(2)2.758(1)<Na1!O>

2.425

Na2!O1 62
Na2!O2 62
Na2!O3 62
Na2!O4 62
Na2!Cl

2.893(2)2.432(3)2.689(3)3.010(1)2.696(2)<Na2!O>

2.756

Na3!O1 63
Na3!O2 63
Na3!O3 63
Na3!O43.005(2)2.248(2)3.104(3)2.249(3)<Na3!O>

2.732

S1!O1 62
S1!O2 62

1.467(2)1.470(2)<S1!O>

1.469

1.463

111.1(2)109.9(1)108.9(1)108.0(2)109.5

110.5(1)109.5(1)109.4(1)108.6(1)109.5

O1!S1!O1
O1!S1!O2 62
O1!S1!O2 62
O2!S1!O2<O!S1!O>

0.20
0.16
0.19
0.15
0.14
0.17
S = 1.01

2.349(1)2.419(1)2.355(1)2.489(1)2.504(1)2.767(1)2.423

0.06 62
0.16 620.10 620.05 620.19
S = 0.93

2.882(1)2.449(1)2.680(1)3.008(1)2.667(1)0.07 62
0.16 620.10 620.05 620.20
S = 0.96

2.755
0.05 63
0.24 63
0.04 63
0.24
S = 1.23

3.034(1)2.177(1)3.202(1)2.161(1)0.05 63
0.28 63
0.03 63
0.29
S = 1.37

2.740
1.53 62
1.52 62
S = 6.10

1.56 63
1.61
S = 6.29

1.460(1)1.465(1)S2!O3 63
S2!O4

1.460(3)1.447(3)<S2!O>

1.457

1.432

111.8(1)
107.1(1)
109.5

112.9(1)105.8(1)
109.4

O3!S2!O3 63
O3!S2!O4 63<O!S2!O>

0.20
0.17
0.19
0.15
0.14
0.17
S = 1.02

The chemical formula obtained from therefinement for d’ansite (Fe), Na 21.48 Fe 0.52
(SO4)10Cl3, is in good agreement with theformula calculated from the chemical analyses
and has 22.52 positive charges for the cation sum,compared to 23 negative charges of the anions.
This result can be considered to be satisfactory,
especially in view of the weak scattering power ofthe crystal as a result of its small size

1.431(1)1.436(2)1.56 62
1.54 62
S = 6.20

1.68 63
1.66
S = 6.70(~0.0360.0360.03 mm) and low quality. Finalatom coordinates and displacement parameters
are listed in Tables 4 and 5. Relevant interatomic
distances are listed in Table 6.
Results and discussion

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Our structure refinements of d’ansite (Mn) andd’ansite (Fe) confirm that the correct space group

D’ANSITE (MN) AND D’ANSITE (FE), TWO NEW MINERALS

for the d’ansite mineral series is I4̄3d. A view ofthe structure of d’ansite (Mn) is shown in Fig. 6.
The asymmetric unit contains a site in a general
position (Na1), and another site on a twofold axis
(Na2), both exclusively occupied by Na+; a thirdsite [Na3/Mn or Na3/Fe] on a threefold axis isstatistically occupied by Na+ and Mn2+ (or Fe2+);
two sulfate anions are located about a twofold2!
axis (S1O2!
4 ) and a threefold axis (S2O4 ),respectively and a chloride anion is located on a4̄ position. The coordination geometry of eachsodium site is different. Taking into account someinteratomic distances that are significantly greaterthan the sum of the ionic radii of sodium andoxygen (of ~2.6 Å up to 3.1 Å), the Na1 site canbe considered to have a distorted octahedral
coordination with a mean Na1!O distance of
2.423 and 2.425 Å for the two minerals,
respectively, and a chloride ion in an apical
position at ~2.76 Å from the Na+ ion. The Na2site has a distorted ninefold coordination with amean Na2!O distance of 2.755 and 2.756 Å and a
Na2!Cl distance of ~2.68 Å. Partial substitutionof Na for Mn or Fe occurs at the Na3 site, which

has a coordination number of 10, and a mean
Na3!O distance of 2.732 and 2.740 Å (Fig. 7).
The chloride ion is octahedrally coordinated in a
[ClNa6 ]5+ moiety, with an average Na!Cl
distance of 2.736 Å, which is slightly but
significantly shorter than the corresponding
distance in sodium chloride (2.820 Å). A bondvalence analysis carried out using the parametersof Brown (2009) (Table 6) is in agreement withthe exclusive occupation of the Na1 and Na2 sites
by sodium, and with partial replacement of
sodium by a divalent cation at the Na3 site.
The sulfate anions have an average S!O
distance which is comparable to the grand meanvalue found in sulfate minerals (1.473 Å;Hawthorne et al., 2000), with a significant
difference in the case of d’ansite (Fe) probably
due to the lower accuracy of the diffraction data
resulting from the poorer quality of the crystal.
This difference reflects also in an overestimationof the valency of S2 calculated using the bondvalence parameters reported in Brown andAltermatt (1985) in comparison to the theoreticalvalue of 6.

FIG. 6. A projection along [100] of the crystal structure of d’ansite (Mn), which is made up of [ClNa6]5+, Na+/Mn2+
cations and SO2!
4 tetrahedra.

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F. DEMARTIN ET AL.

FIG. 7. The coordination polyhedra of the Na sites.

This report of d’ansite (Mn) and d’ansite (Fe)from Vesuvius and Vulcano is the first record ofd’ansite series minerals from fumaroles, anenvironment which differs substantially from theevaporites from which the magnesium analogue,d’ansite, was first described. We have recently
been informed that d’ansite (Fe) has also beenfound as a secondary mineral at Mežica(Slovenija), where it is associated with d’ansite
and metasideronatrite 2M (M. Ciriotti, pers.
comm.).
Acknowledgements
The authors thank the referees Anna Garavelli,
Anthony Kampf, Peter Leverett and Principal
Editor Peter Williams for useful suggestions.
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