Eur. J. Mineral., 32, 57–66, 2020
https://doi.org/10.5194/ejm-32-57-2020© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Aluminosugilite, KNa2Al2Li3Si12O30, an Al analogue ofsugilite, from the Cerchiara mine, Liguria, Italy
Mariko Nagashima1 , Chihiro Fukuda2 , Takashi Matsumoto3 , Teruyoshi Imaoka1 , Gianluca Odicino4 ,and Gianluca Armellino5
1 Graduate school of Sciences and Technology for Innovation, Yamaguchi University,

Yoshida 1677-1, Yamaguchi 753-8512, Japan
2 Gem Research Japan Inc., Nagahorido BLDG 5F 1-3-10, Higashi-Shinsaibashi,

Chuo-ku, Osaka 542-0083, Japan
3 Application Laboratories, Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan
4 Associazione Micro-mineralogica Italiana, via Fasceto 15, 16032 Camogli, Genoa, Italy
5 Associazione Micro-mineralogica Italiana, via Piani del Monastero 17, 17017 Millesimo, Savona, Italy

Correspondence: Mariko Nagashima (nagashim@yamaguchi-u.ac.jp)
Received: 28 June 2019 – Accepted: 16 September 2019 – Published: 16 January 2020

Abstract. Aluminosugilite (IMA2018-142), ideal formula KNa2 Al2 Li3 Si12 O30 , is a new mineral that was foundin the interstices in manganiferous metacherts from the Cerchiara mine, Liguria, Italy. Aluminosugilite is an Al
analogue of sugilite belonging to the milarite group. It occurs as aggregates of small prismatic and/or granular
crystals up to 1 mm in length, and it is pinkish-purple with a pale purple to white streak and a vitreous lustre.
It has a Mohs hardness of 6–6.5. Its cleavage is indistinct, poor on (0001). Measured and calculated densities
are Dmeas. = 2.71–2.72 g cm−3 and Dcalc. = 2.73 g cm−3 , respectively. Aluminosugilite is optically uniaxial (–),
with ω = 1.577–1.586 and ε = 1.575–1.585, with a weak pleochroism. The magnetic susceptibility is lower thanthat for sugilite. Aluminosugilite is insoluble in HCl, HNO3 and H2 SO4 , like sugilite. The empirical formula ofaluminosugilite calculated on the basis of O = 30 from the result obtained by electron microprobe analysis and3+laser-induced breakdown spectroscopy is K0.99 Na1.99 (Al1.38 Mn3+
0.31 Fe0.24 Ti0.05 Mg0.01 )61.99 Li3.06 Si11.99 O30 .
Structure refinement converged to R1 = 2.17 %. Its space group is hexagonal P 6/mcc, with unit-cell parameters a = 9.9830(4) Å, c = 13.9667(5) Å and V = 1205.45(7) Å3 . Based on the refined site occupancies, theT2 T1ideal structural formula of aluminosugilite is C KB NaA
2 Al2 Li3 Si12 O30 . The variation of the A–O3 distance isgoverned by the cationic substitution at the A site. The a and c dimensions of aluminosugilite are shorter thanthose of sugilite due to Al substitution for Fe3+ at the A site.

1

Introduction

Aluminosugilite(IMA2018-142),
ideal
formulaKNa2 Al2 Li3 Si12 O30 , was found in manganiferous
metacherts from the Cerchiara mine, Liguria, Italy. To
the best of our knowledge, this is the ninth new mineral
species discovered from this locality. For instance, oneof the new species from this locality was the Li-bearing
mineral, balestraite KLi2 V5+ Si4 O10 O2 (Lepore et al.,2015). Aluminosugilite is an Al analogue of sugilite,
KNa2 Fe3+
2 Li3 Si12 O30 (Murakami et al., 1976; Kato et al.,
1976; Armbruster and Oberhänsli, 1988) belonging to themilarite group, which is also known as the osumilite group(synonymous). Milarite-group minerals are chemically very
diverse. More than 20 independent species are currently
known (see Table 2 in Gagné and Hawthorne, 2016; also
Table S1 in the Supplement linked to this article and freely
available at https://pubs.geoscienceworld.org/eurjmin, lastaccess: 30 October 2019). Its general formula is representedIV
XII IVas VI AIX2 B2 C (T 2)3 (T 1)12 O30 (e.g. Forbes et al.,1972), where A = Al, Fe3+ , Fe2+ , Mg, Zr, Sn, Y, Ca, Sc andothers; B = K, Na,  (vacant), H2 O; C = K, Na, Ba, (vacant); T 1 = Si, Al; T 2 = Li, Be, B, Mg, Al, Si, Zn, Fe2+ ,Published by Copernicus Publications on behalf of the European mineralogical societies DMG, SEM, SIMP & SFMC.

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M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy

Mn2+ . Milarite-group minerals are double-ring silicates withmaximum topological symmetry of space group P 6/mcc.
However, cation or vacancy order may lead to symmetry
lowering, for example armenite (Armbruster and Czank,
1992; Armbruster, 1999) and roedderite (Armbruster, 1989).
The crystal structure is characterized by two T 16 O18 rings oftetrahedra forming a T 112 O30 double-ring through linkagesof their apical vertices. Heterovalent (coupled) substitutions
among the A, B and T 2 sites are common in this group,
leading to the observed chemical variability.
The mineral aluminosugilite is named after sugilite,
which has Fe3+ -dominant composition at the A site. Thus,“alumino-” is added as prefix in accordance with the guideline on mineral nomenclature of the IMA Commission(Nickel and Grice, 1998), especially on the use of prefixes
and suffixes (Hey and Gottardi, 1980). Sugilite was named
by Murakami et al. (1976) in honour of late Ken-ichi Sugi
(1901–1948) of the Kyushu Imperial University, who firstfound the occurrence of sugilite on the Iwagi Islet, Ehime,
Japan, representing the type locality of sugilite. The typespecimen of aluminosugilite will be deposited in the National Museum of Nature and Science, Tsukuba, Japan, under the specimen number NSM-MF-16503 (holotype). In thepresent study, the new mineral from the Cerchiara mine was
examined using electron microprobe analysis (EMPA), laserinduced breakdown spectroscopy (LIBS) and X-ray singlecrystal diffraction methods. In addition, sugilite from theIwagi Islet was also studied as a reference material for further
understanding.
2

Occurrence

Aluminosugilite was found in the interstices in manganiferous metacherts from the Cerchiara mine, Faggiona, Borghetto Vara-Pignone, La Spezia, Liguria, Italy(44.116◦ N, 9.420◦ E). Mineral assemblages, mineralizationof Mn ores and ore genesis of the Cerchiara mine were studied by Lucchetti et al. (1988) and Cabella et al. (1998). The
Cerchiara mine exploited braunite and hematite until 1945. It
is a manganese and iron ore deposit hosted in Jurassic ophiolitic metacherts consisting of braunite with minor quartz
layers interbedded with hematite and quartz bands formedat condition of prehnite–pumpellyite facies (Lucchetti et al.,
1988; Cabella et al., 1998). The ore was produced by precipitation from submarine hydrothermal vents and reworked byturbiditic resedimentation (Cabella et al., 1998). According
to Lucchetti et al. (1988), the two very common assemblagesof ores are braunite + quartz and hematite + quartz, and mineral assemblages are characterized by Na-clinopyroxene, alkali and sodic-calcic amphiboles, andradite, piemontite, pectolite, ganophyllite, and carbonates. In particular, the compositional variety of Na-clinopyroxene is distinct, which varies
from pure aegirine to aegirine–augite with variable Mg, Mn
and Ca contents.

Eur. J. Mineral., 32, 57–66, 2020

The presence of hematite and braunite as main constituentsof the ore body suggests highly oxidizing conditions. The
mineralization at the Cerchiara mine experienced hydrothermal metasomatism induced by diffuse interaction with alkalirich fluids, which produced peculiar mineral assemblages
enriched in Na, K and Li and provided also appreciable
amounts of Ba, Sr, Ca and Cu (e.g. Kolitsch et al., 2018).
Aluminosugilite is one of the representative (Na, K, Li)-richminerals formed under alkali-rich and oxidized conditions.
The sugilite-type mineral from the Cerchiara mine was
first reported by Cabella et al. (1990). According to theirstudy, it occurs in very compact aggregates filling veins in
the metacherts, and its aggregate commonly contains fibrous
pectolite. Chemical heterogeneity of sugilite due to Mn3+ –Al substitution was reported in their study. The Mn2 O3 andAl2 O3 contents in sugilite range between 1.5 wt %–6.5 wt %and 5.8 wt %–9.7 wt %, respectively (Table 1 in Cabella etal., 1990). In their study, it was presented as Al-rich, Fe-poor
manganoan sugilite. They confirmed the significant amountof lithium in sugilite by means of atomic absorption determination; however, the difficulty to remove very fine inclusionsof fibrous pectolite did not allow them to provide a reliable
composition. On the other hand, in our specimens collectedby one of the authors (Gianluca Armellino) in 1997, aluminosugilite was closely associated with quartz and K-feldspar,
but close association with pectolite was not observed. Sugilite at Cerchiara was originally described (Lucchetti et al.,1988) as forming big zoned purple veins of some centimetres height, sometimes interleaved with light-blue richteriteveins and braunite, but several other occurrences followed in
the last 30 years in the abandoned dumps and in the bed of
Redarena Creek, where sugilite may form prismatic euhedral
purple crystals up to 3 mm long.

3

Appearance, physical and optical properties

Aluminosugilite commonly occurs as aggregates of small
prismatic and/or granular crystals up to 1 mm in length(Fig. 1). Although the Fe analogue of sugilite from the Iwagi
Islet is known to show brownish-green colour, aluminosugilite from the Cerchiara mine is pinkish-purple with pale purple to white streak and a vitreous lustre. It has a Mohs hardness of 6–6.5. Its cleavage is indistinct, poor on (0001). The
density, determined by the floatation method using heavy
liquids, is 2.71–2.72 g cm−3 , which is consistent with thedensity of 2.73 g cm−3 calculated using the empirical formula and unit-cell volume refined from single-crystal X-ray
diffraction data. Aluminosugilite is optically uniaxial (–),
with ω = 1.577–1.586 (avg 1.581) and ε = 1.575–1.585 (avg
1.580). The refractive indices were determined using straypreparation of several small crystals in immersion oil after
Danhara et al. (1992). The mineral has weak pleochroism.
The Gladstone–Dale compatibility index of aluminosugilite(1 – KP /KC ) calculated with the measured density (avg
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M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy
4

Figure 1. Microphotograph of aluminosugilite.

2.71 g cm−3 ) and average chemical composition listed in Table 1 is +0.003 and falls into the “superior” category according to Mandarino (1981).
The magnetic susceptibility of aluminosugilite from the
Cerchiara mine and sugilite from Iwagi Islet were comparedby measurements with a Frantz isodynamic separator at room
temperature and at a forward slope of 15◦ and a slide tilt of
25◦ . The aluminosugilite and sugilite were attracted to themagnet at 0.9 and 0.6 A, respectively, indicating lower magnetic susceptibility of aluminosugilite than for sugilite. Bothspecimens did not contain visible impurities. The result isin good agreement with the lower total Fe + Mn content ofaluminosugilite compared to sugilite.
Both specimens are insoluble in hydrochloric acid (HCl),nitrous acid (HNO3 ) and sulfuric acid (H2 SO4 ), according
to chemical tests performed after the method of Jones andFleming (1965).

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59

Experimental methods

Chemical analyses of aluminosugilite and sugilite were performed using an electron microprobe analyser (EMPA, JEOL
JXA-8230) installed at the Centre for Instrumental Analysis, Yamaguchi University, Japan. The Li2 O concentrationof aluminosugilite was analysed using laser-induced breakdown spectroscopy (LIBS, Applied spectra J200-EC) at Gem
Research Japan, Osaka, Japan, whereas the difference to
100 wt % of the EMPA data in sugilite was assumed to be
Li2 O. Operating conditions for EMPA were as follows: accelerating voltage of 15 kV, a beam current of 20 nA anda beam diameter of 1–5 µm. Wavelength-dispersion spectra were collected using LiF, PET and TAP monochromator
crystals to identify interfering elements and locate the best
wavelengths for background measurements. The abundancesof Si, Ti, Al, Cr, V, Fe, Mn, Ni, Mg, Ca, Sr, Ba, Na, K, P,
F and Cl were measured. Several elements, which are notshown in Table 1, are below the detection limit. The ZAF
correction method was applied to all elements. The Li concentration for separated aluminosugilite grains mounted on a
glass slide with petropoxy resin was determined using LIBS.
The LIBS employed a 266 nm Nd:YAG laser coupled with
an optical emission spectrometer. The employed Li peak was
at a wavelength of 670.706 nm. All analyses were carried out
under a He gas flow of 1.0 L min−1 with a laser pulse energyof 10 mJ at 10 Hz using a laser beam diameter of 35 µm. The
gate delay and pre-ablation times were 0.3 µs and 0.3 s, respectively, and 25 shots were used for calculations. Emission
spectra were collected in the 185.177–1050.782 nm spectral
range covering the main emission lines of major elements(Na, Li, Al, Si, K). The NIST SRM 610 and 612 glasses anda synthetic Li glass were used as calibration standards covering the Li2 O concentration range between 86.5 ppm (NIST612) and 5 wt % (Li glass).
X-ray powder diffraction data were collected using a
Rigaku MiniFlex automated X-ray powder diffractometer installed at the Centre for Instrumental Analysis, Yamaguchi
University. The Cu X-ray tube for CuKα line (λ = 1.5418 Å)
was operated at 40 kV and 15 mA. Profile was taken over2θ = 3–70◦ with a step interval of 0.01◦ .
X-ray diffraction data for a single crystal of aluminosugilite (0.038 mm × 0.036 mm × 0.028 mm) were collected using a Rigaku MM007 rotating anode generator equipped with VariMax optics, an AFC10 goniometerand HyPix-6000HE detector at Rigaku Corporation, Japan.
The crystal was mounted on a glass fibre, and intensity
data were measured at room temperature using MoKα
radiation (λ = 0.71073 Å). Preliminary lattice parameters
and an orientation matrix were obtained from six sets offrames and refined during the integration process of theintensity data. The diffraction data were processed using
CrysAlisPro (Rigaku Oxford Diffraction, 2018). An empirical absorption correction using CrysAlisPro (Rigaku Oxford Diffraction, 2018) was applied. The diffraction data ofEur. J. Mineral., 32, 57–66, 2020

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M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy

Table 1. Chemical compositions of aluminosugilite and sugilite, in addition to reference materials.
Aluminosugilitea

SampleSugiliteb

Reference materials

Constituent(wt %)

Avg

Range
n = 35

SD

Avg

Range
n = 22

SD

SiO2
TiO2
Al2 O3Fe2 O3 c
Mn2 O3 c
MgO
CaO
Na2 O
K2 O
Li2 O

72.20
0.43
7.06
1.92
2.42
0.04
0.01
6.17
4.68
4.59

70.51–74.23
0.15–1.15
5.03–9.44
0.69–5.60
0.48–4.43
0.00–0.65
0.00–0.10
5.99–6.43
4.39–4.86
4.33–4.70

0.73
0.25
1.22
0.91
1.31
0.10
0.01
0.09
0.09
0.08

70.47
0.65
1.81
11.89
0.02
0.01
0.04
5.97
4.69
4.45

69.62–71.16
0.16–1.67
1.48–2.30
10.50–12.60
0.00–0.07
0.00–0.03
0.00–0.31
5.78–6.11
4.55–4.76

0.32
0.39
0.25
0.55
0.02
0.01
0.07
0.08
0.05

Normalized as
Si
Ti
Al
Fe3+
Mn3+
Mg
Ca
Na
K
Li

99.52
O = 3011.99 11.94–12.04
0.05
0.02–0.14
1.38
1.00–1.85
0.24
0.09–0.71
0.31
0.06–0.57
0.01
0.00–0.16
0.00
0.00–0.02
1.99
1.94–2.03
0.99
0.93–1.03
3.06
2.94–3.14

0.02
0.03
0.23
0.11
0.17
0.03
0.00
0.02
0.02
0.06

100.00Si = 12
12
0.08
0.36
1.52
0.00
0.00
0.01
1.97
1.02
3.05

0.02–0.21
0.30–0.46
1.35–1.61
0.00–0.01
0.00–0.01
0.00–0.06
1.90–2.02
0.99–1.03

0.05
0.05
0.07
0.00
0.00
0.01
0.03
0.01

Total

20.02

NaAlSi3 O8
TiO2
Al2 O3Fe2 O3MnO
MgO
CaSiO3
NaAlSi3 O8
KAlSi3 O8–

20.02

a Li O content was analysed by LIBS (number of analytical points = 48). Si content obtained by EMPA was used as an internal standard to2
estimate the Li content. b Difference of total oxide wt % from 100 wt % was assumed to be Li2 O content. c Fe as Fe2 O3 and Mn as Mn2 O3 .

sugilite (0.03 mm × 0.04 mm × 0.04 mm) were collected atroom temperature with graphite-monochromated MoKα Xradiation using a Bruker SMART APEX II CCD diffractometer installed at Shimane University, Japan. Preliminary
lattice parameters and an orientation matrix were obtained
from 12 sets of frames and refined during the integration
process of the intensity data. Diffraction data were collectedwith ω scans with different ϕ settings (ϕ–ω scan) (Bruker,
1999). Data were processed using SAINT (Bruker, 1999). An
empirical absorption correction using SADABS (Sheldrick,1996) was applied. The quality of the data obtained from theIwagi sugilite was low (Rint = 11 %) because only a crystalof low quality due to metasomatic origin was available. For
both samples, structural refinements were performed using
SHELXL-97 (Sheldrick, 2008). Scattering factors for neutral atoms were employed. The reflection statistics and systematic absences were consistent with space groups P 6/mcc.
The site occupancies of the C, T 1 and T 2 sites were refinedwith K, Si and Li without restraints in our preliminary refinements, respectively. They turned out to be fully occupied
within standard deviation in both specimens. Thus, the site
occupancies at the C, T 1 and T 2 sites were fixed as 1.0 K,

Eur. J. Mineral., 32, 57–66, 2020

1.0 Si and 1.0 Li, respectively. The A site was refined with
Al and Fe scattering factors. Fe, Mn and Ti cannot be distinguished due to their similar atomic-scattering factors. Thus,
the Fe occupation at the A site actually represents 6(Fe +Mn) for aluminosugilite and 6(Fe + Ti) for sugilite. In casethat Na at the B site was refined with (x, y, z) = (1/2, 2/3, 0)(site symmetry 6̄), an unreasonably large displacement parameter elongated along the c axis was obtained. An additional degree of freedom, z parameter for Na, leads to morereasonable displacement parameters. It is suggested that Nain this structure is disordered at 1/2, 2/3, 0.008(6) for aluminosugilite and 1/2, 2/3, 0.012(4) for sugilite (site symmetry 3), the so-called B 0 site (Abraham et al., 1983). The Nasite has distorted 9-fold coordination. A similar coordinationof Na was found for sugilite by Armbruster and Oberhänsli
(1988). The site occupancy at the B 0 site was 48(2) % of Na
indicating full occupancy within standard deviation. Thus,
the value was fixed to 0.5 Na, the maximum crystallographic
occupancy for this split site.

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M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy

61

Figure 2. Crystal structure of aluminosugilite drawn with VESTA3 (Momma and Izumi, 2011). The A octahedra are occupied by octahedral
trivalent cations, such as Al, Fe3+ and Mn3+ . The B 0 and C sites are occupied by Na and K, respectively. The T 1 tetrahedra consist of
double-ring units. The large T 2 tetrahedra centred by Li are strongly angularly distorted. The B 0 site is located at 1/3, 2/3, z.

5Chemical data

Chemical compositions of aluminosugilite and sugilite,
in addition to probe standards, are listed in Table 1. Although each crystal is relatively homogeneous in general,
some crystals show the chemical variation characterized
by Al↔Fe3+ and/or Al↔Mn3+ substitutions. The Fe2 O3
and Mn2 O3 contents attain up to 5.60 wt % and 4.43 wt %,respectively. Even in such Fe3+ - and/or Mn3+ -enrichedparts, aluminium ions are still dominant among the octahedral cations. Based on the structural analysis, there
is no evidence of an OH group or H2 O in the crystal
structure of aluminosugilite. The empirical formula ofaluminosugilite calculated on the basis of O = 30 using theresult obtained by EMPA and LIBS (Table 1) is as follows:
3+
K0.99 Na1.99 (Al1.38 Mn3+
0.31 Fe0.24 Ti0.05 Mg0.01 )61.99 Li3.06
Si11.99 O30 . The ideal formula is KNa2 Al2 Li3 Si12 O30 , which
requires (in wt %) 73.81 SiO2 , 10.44 Al2 O3 , 6.34 Na2 O, 4.82
K2 O and 4.59 Li2 O, total 100 wt %. Al- and Mn-rich sugilite
has been also reported from the Furumiya mine, Ehime,
Japan (Hirowatari and Fukuoka, 1989). Their chemicalcompositions possibly correspond to aluminosugilite and“manganisugilite” based on the ratios of the A site cations
such as Al, Fe3+ and Mn3+ . The Al2 O3 and Mn2 O3 contents in Furumiya sugilite reach 5.364 wt % and 7.84 wt %,respectively.
Sugilite from Iwagi Islet is rich in Fe and poor in
Al. The Mn2 O3 content is negligible. According to theaverage composition (Table 1), the chemical formula is
K1.02 (Na1.97 Ca0.01 )61.98 (Fe3+
1.52 Al0.36 Ti0.08 )61.98 Li3.05 Si12
O30 . Although Kato et al. (1976) suggested that Na shared
the B site with H2 O in the Iwagi sugilite, our preliminaryrefinement indicates that the B 0 site is fully occupied by Na
within standard deviation and the presence of H2 O was notsupported by the result of chemical analysis. Furthermore,
the DTA–TGA analysis of sugilite from the Wessel mine,www.eur-j-mineral.net/32/57/2020/

South Africa, by Dunn et al. (1980) did not indicate thepresence of volatiles.
6

X-ray crystallography and crystal-structure
determination

The observed and calculated X-ray powder patterns of aluminosugilite are listed in Table S2 in the Supplement. The
calculated pattern was obtained based on the result of singlecrystal analysis mentioned below. The cell parameters determined from powder data are a = 9.954(7) Å, c = 13.95(4) Åand V = 1197(4) Å3 , which is slightly smaller than those obtained from X-ray single-crystal method.
Crystallographic data of aluminosugilite and sugilite aresummarized in Table 2. The crystal structure of aluminosugilite is shown in Fig. 2. Refinements of the structure converged to R1 = 2.17 % for aluminosugilite and3.32 % for sugilite. The determined cell parameters are a =9.9830(4) Å, c = 13.9667(5) Å and V = 1205.45(7) Å3 foraluminosugilite, and a = 10.0248(7) Å, c = 14.0310(7) Åand V = 1221.15(2) Å3 for sugilite. The refined site occupancies, atomic coordinates and anisotropic displacement parameters are listed in Table 3, selected interatomic distances
and angles in Table 4. Based on the refined site occupancies,
the structural formula of aluminosugilite is represented as
3+ T 2T1
C KB NaA (Al
3+ =1.26(1) Me0.74 )62.00 Li3 Si12 O30 , where Me
2
3+
3+
Mn + Fe . The A site is predominantly occupied by Al.
Based on the Mn : Fe ratio obtained by EMPA, 56 : 44, thesite occupancy of the A site in aluminosugilite is assumed to3+
be Al0.629(6) Mn3+
0.21 Fe0.16 . On the other hand, Fe dominates
the A site in sugilite. The structural formula of the Iwagi
3+
T1
T2
sugilite is C KB NaA
2 (Fe1.47(2) Al0.53 )62.00 Li3 Si12 O30 . Traceamount of Ti may be present with Fe on a basis of chemical analysis (Table 1). The cation assignments in the present
study are similar to those suggested for the Wessels minesugilite by Armbruster and Oberhänsli (1988). On the other
hand, Kato et al. (1976) reported that the cation distributions
Eur. J. Mineral., 32, 57–66, 2020

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M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy

Table 2. Experimental details of the single-crystal X-ray diffraction analysis of aluminosugilite and sugilite crystals.
SampleAluminosugilite

SugiliteSpace group
Crystal size (mm)P 6/mcc0.038 × 0.036 × 0.028

0.03 × 0.04 × 0.04

9.9830(4)13.9667(5)1205.45(1)10.0248(7)14.0310(7)1221.15(2)

2.73

2.77

Cell parameters

a (Å)
c (Å)
V (Å3 )

Dcalc. (g cm−3 )Radiation
Monochromator
Diffractometer
Scan type
Absorption correction
θmin (◦ )θmax (◦ )µ (mm−1 )Collected reflections
Unique reflections
Rint (%)
Rσ (%)
Index limits
Refinement on F 2 using
R1 (%)wR2 (%)
No. of parameters
Weighting scheme∗
1ρmax (e Å−3 )1ρmin (e Å−3 )MoKα (λ = 0.71073 Å)
VariMax optics
RIGAKU HyPix-6000HE
ω scanCrysAlisPro (Rigaku Oxford Diffraction, 2018)
2.4
29.5
1.34
8821
590
2.43
1.27
−10 ≤ h ≤ 12, −13 ≤ k ≤ 9, −19 ≤ l ≤ 17
SHELXL-97 (Sheldrick, 2008)
2.17
5.99
45
w = 1/[σ 2 (Fo2 ) + (0.0252P )2 ] + 1.83P
0.35 at 0.74 Å from O2−0.46 at 0.61 Å from B

Graphite
Bruker APEXII CCD
φ − ω scan (Bruker, 1999)
SADABS (Sheldrick, 1996)
2.3
25.4
1.83
6453
402
11.00
4.39
−11 ≤ h ≤ 12, −12 ≤ k ≤ 11, −16 ≤ l ≤ 15
3.32
7.32
45
w = 1/[σ 2 (Fo2 ) + (0.0270P )2 + 3.24P ]0.41 at 0.61 Å from O2−0.41 at 3.19 Å from O2∗ The function of the weighting scheme is w = 1/(σ 2 (F 2 ) + (a · P )2 + b · P ), where P = (Max(F 2 ) + 2F 2 )/3, and the parameters a and b are chosen to minimize theoocdifferences in the variances for reflections in different ranges of intensity and diffraction angle.

of T 2 and A in Iwagi sugilite were (Li2.12 Al0.59 Fe3+
0.29 ) and
2+
(Fe3+
Na
Ti
Fe
),
respectively.
At
least,
thenumber
0.59 0.06 0.03
1.32
of electrons at each site obtained in the present study cannot support their cation assignments. Armbruster and Oberhänsli (1988) pointed out that the overestimated scattering
power of the cations at T 2 and erroneous wet-chemical analyses possibly led to the questionable cation assignments reported in Kato et al. (1976).
As mentioned above, the A site in aluminosugilite is predominantly occupied by the smaller Al ions (0.535 Å: Shannon, 1976), whereas in sugilite the larger Fe3+ ions (0.645 Å)
prevail. The variation of the A–O3 distance, 1.940 Å in aluminosugilite (this study) and 1.972–1.981 Å in sugilite (thisstudy; Armbruster and Oberhänsli, 1988), is governed by thecationic substitution at the A site. Isotropic expansion due toFe3+ substitution for Al lengthened the a and c dimensionsof sugilite compared to aluminosugilite. In general, the a andc dimensions of the milarite-group minerals are known as
ca. 10 and 14 Å, respectively (see Table 6 in Armbruster andOberhänsli, 1988). After Armbruster and Oberhänsli (1988),
the length of a dimension varies with that of the shared edge

Eur. J. Mineral., 32, 57–66, 2020

between the T 2O4 -tetrahedra and AO6 octahedra. The oxygen coordination of Li is known to vary from 3 to 8. After
Wenger and Armbruster (1991), tetrahedral coordination ispreferred, and IV < Li–O> is estimated as 1.96(3) Å basedon the simplified potential energy. In fact, the estimated <Li–
O> distance corresponds to that observed in aluminosugiliteand sugilite (Table 4).
In sugilite structures, the strongly angularly distorted
T 2(Li)O4 tetrahedron is connect to the fairly regular AO6
octahedron. The shorter O3–O3 edges may lead to the greaterbond variance of the T 2O4 tetrahedron: 545.8 in aluminosugilite and 488–502 in sugilite according to Baur (1974). The
T 2 tetrahedron occupied by Li in sugilites is relatively large
compared to that occupied by Al, as exemplified by osumilite (ionic radius of IV Li+ = 0.59 Å and VI Al = 0.39 Å;
Shannon, 1976). While the T 2–O3 distance in sugilite is
1.97 Å, that in osumilite is approximately 1.63 Å. Although
the T 2O4 tetrahedron in osumilite is less distorted and its
bond variance is much smaller than that of sugilite (238.6
in osumilite; Winter et al., 1995), such a small less-distorted
T 2 site compresses the edge-shared AO6 octahedron (Armbruster and Oberhänsli, 1988). It makes the c dimensionwww.eur-j-mineral.net/32/57/2020/

M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy

63

Table 3. Refined atomic coordinates, displacement parameters, and site occupancies of aluminosugilite and sugilite.
SampleAluminosugilite

Sugilite∗∗

B0

Aluminosugilite

Sugilite

Na0.5
1/3
2/3
0.008(6)0.035(8)0.0209(7)0.0209(7)0.06(2)0.0105(3)

Na0.5
1/3
2/3
0.012(4)0.026(8)0.0205(17)0.0205(17)0.04(2)0.0103(8)

A
x
y
z
U eq
U 11
U 22
U 33
U 12
C
x
y
z
U eq
U 11
U 22
U 33
U 12

Al0.629(6) Fe0.371
1/3
2/3
1/4
0.0057(3)0.0054(3)0.0054(3)0.0064(4)0.00268(15)
K1.0
0
0
1/4
0.0175(3)0.0162(4)0.0162(4)0.0201(6)0.0081(2)Fe0.735(12) Al0.265
1/3
2/3
1/4
0.0051(6)0.0044(7)0.0044(7)0.0062(9)0.0022(3)
K1.0
0
0
1/4
0.0202(9)0.0181(13)0.0181(13)0.024(2)0.0091(6)

U eq
U 11
U 22
U 33
U 12
O1
x
y
z
U eq
U 11
U 22
U 33
U 12

0.1400(2)0.3987(2)00.0165(4)0.0205(10)0.0185(9)0.0083(7)0.0081(8)0.1386(5)0.3976(5)00.0164(10)0.020(3)0.016(2)0.010(2)0.007(2)

T1
x
y
z
U eq
U 11
U 22
U 33
U 23
U 13
U 12

Si1.0
0.23601(5)0.35791(5)0.38651(3)0.00726(14)0.0070(2)0.0077(2)0.0074(2)0.00043(15)0.00035(15)0.00394(17)Si1.00.23658(14)0.35605(13)0.38701(8)0.0081(3)0.0084(7)0.0084(6)0.0082(6)0.0003(5)0.0000(5)0.0048(5)

O2
x
y
z
U eq
U 11
U 22
U 33
U 23
U 13
U 12

0.22500(15)0.27827(15)0.13799(9)0.0143(3)0.0134(6)0.0156(6)0.0188(6)−0.0005(5)−0.0001(5)0.0109(5)0.2224(3)0.2770(3)0.13742(19)0.0142(8)0.0130(16)0.0147(17)0.0184(16)0.0021(14)0.0008(14)0.0094(14)

T2
x
y
z
U eq
U 11
U 22
U 33
U 12

Li1.0
1/2
1/2
1/4
0.0156(11)0.018(2)0.018(2)0.015(2)0.012(3)

Li1.0
1/2
1/2
1/4
0.012(3)0.009(5)0.009(5)0.018(7)0.004(6)

O3
x
y
z
U eq
U 11
U 22
U 33
U 23
U 13
U 12

0.16906(14)0.51105(13)0.17136(8)0.0114(3)0.0111(6)0.0090(5)0.0138(5)−0.0026(5)−0.0006(5)0.0048(5)0.1659(3)0.5084(3)0.1702(2)0.0120(7)0.0104(16)0.0112(16)0.0148(15)−0.0030(14)−0.0010(12)0.0056(13)xyz∗ Fe represents 6 (Fe+Mn) in aluminosugilite and 6 (Fe+Ti) in sugilite.

shorter. The dominant T 2 and A cations thus govern thevariation of a and c dimensions. Although the dominant influence of the C–O distance on the c dimension was also
pointed out (Armbruster and Oberhänsli, 1988), the C site
is fully occupied by potassium and shows no compositionalvariation in the case of aluminosugilite and sugilite.

www.eur-j-mineral.net/32/57/2020/

7

Recommended nomenclature of the milarite-groupmineralThe structural formula of milarite-group minerals is
IV
XII IV
represented as VI AIX
Het2 B2 C (T 2)3 (T 1)12 O30 .
erovalent (coupled) substitutions among the A, B andT 2 sites are common in this group, leading to thechemical variability of the group (Table S1). On theother hand, the species only related to the homovalent
Eur. J. Mineral., 32, 57–66, 2020

64

M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy

Table 4. Selected interatomic distances (Å) and angles (◦ ) of aluminosugilite and sugilite.
SampleAluminosugilite

Sugilite

A–O3 (×6)

1.9395(12)1.981(3)B 0 –O1 (×3)
B 0 –O3 (×3)
B 0 –O3 (×3)

2.394(5)2.78(7)2.98(7)2.419(5)2.75(4)3.03(5)

C–O2 (×12)

2.9950(13)2.997(3)

T 1–O1T 1–O2
T 1–O2
T 1–O3< T 1–O>
O1–T 1–O2
O1–T 1–O3
O2–T 1–O1O2–T 1–O3
O2–T 1–O2O3–T 1–O2

1.6240(6)1.6207(13)1.6172(12)1.5788(12)1.6102108.11(9)108.35(9)110.56(8)111.27(7)104.14(9)114.32(7)1.6260(14)1.621(3)1.619(3)1.575(3)1.610
108.0(2)108.0(2)111.0(2)111.6(2)103.7(2)114.5(2)T 2–O3 (×4)
O3–T 2–O3
O3–T 2–O3
O3–T 2–O3

1.9700(12)84.21(7)112.23(7)136.28(7)1.972(3)86.1(2)110.8(2)135.4(2)

T 1–O1–T 1
T 1–O2–T 1
T 1–O3–T 2

154.85(14)152.67(9)113.51(7)154.3(3)152.4(2)114.5(2)cationic substitution at the A site are also observed asfollows: Fe2+ ↔Mg substitution between osumilite andC KA (Fe2+ , Mg)T 2 AlT 1 (Al Si )O
osumilite-(Mg),
2 10
30
3
2
(Miyashiro, 1956; Chukanov et al., 2013), Zr↔Sn↔Ti
substitution among sogdianite, brannockite and berezanskite, C KA (Zr, Sn, Ti)T2 2 LiT3 1 Si12 O30 (Dusmatov et al.,
1968; White Jr. et al., 1973; Pautov and Agakhanov,1997), Mn↔Ca substitution between dusmatovite
C KB ( K)A (Mn, Ca)T 2 ZnT 1 Si O
andshibkovite,
12 30
2
2
3
(Pautov et al., 1996, 1998), and milarite and almaruC KA (Ca, Mn)T 2 (Be Al)T 1 Si O
dite,
(Černý
et
2
12 30
2
3
al., 1980; Mihajlović et al., 2004), and Y↔Sc substitution between oftedalite and agakhanovite-(Y)C KA [(Sc, Y)Ca]T 2 BeT 1 Si O
12 30 (Cooper et al., 2006;
2
3
Hawthorne et al., 2014) (Table S1). Compositional relation
between sugilite and the newly found aluminosugilite
reflects homovalent substitution, Fe3+ ↔Al, at the A site.
Gagné and Hawthorne (2016) summarized chemical andstructural properties of the milarite-type structure and mentioned that “this difference between homovalent and heterovalent substitutions is embedded in the more recent classification/nomenclature scheme for minerals (e.g. arrojadite,
Chopin et al., 2006; tourmaline, Henry et al., 2011; amphibole, Hawthorne et al., 2012), where root compositions
Eur. J. Mineral., 32, 57–66, 2020are assigned a root name and homovalent analogues are
named by adding prefixes or suffixes to the appropriate rootname”. In milarite-group minerals, osumilite-(Mg) has been
approved as an independent species (Chukanov et al., 2013).
In this case a suffix designation was used to characterize thedominant cation at the A site. However, we would have muchpreferred using a prefix for a cation of primary importancein double-ring silicates (A site) following the guideline on
the use of prefix in the mineralogical nomenclature of IMA
Commission (Hey and Gottardi, 1980). The cations at the B
and C channel sites are flexible, and they play a role to maintain charge balance. The C site is generally occupied by K,
but there are also species having Ba or vacancies. The B site
may be empty or can be fully occupied by Na or K. Thus, it issuggested to leave the possibility of a suffix for variation of
the channel sites, B and C. Since the key cation sites to determine the root name have not been defined in milarite groupas it stands, it is too premature to re-name existing minerals.
On the other hand, giving a totally different name is unnecessary and leads to proliferation of species names. This is particularly true for new species which are only differentiatedby the dominant cation at a certain site. Thus, we conclude
that if only the A cation in a newly discovered milarite-groupmineral is different from an existing species, the addition ofa prefix derived from the dominant A cation is reasonable to
avoid further confusion. It may be advisable to revive anddiscuss the nomenclature of milarite-group minerals in thenear future.

Data availability. The CIF files can be obtained from the corresponding author.

Supplement. The supplement related to this article is available online at: https://doi.org/10.5194/ejm-32-57-2020-supplement.

Author contributions. MN designed the project. GO and GA performed the field investigation and sample collection. MN performed
and validated the analyses by EMPA, X-ray powder diffraction and
X-ray single-crystal diffraction using Bruker APEX II. CF performed the analysis by LIBS. TI performed chemical test and themeasurement of magnetic susceptibility. TM collected X-ray singlecrystal diffraction data using a Rigaku MM007. MN and TI discussed all results, and MN wrote the paper.

Competing interests. The authors declare that they have no conflictof interest.

Acknowledgements. We thank Roberto Cabella and Gabriella Lucchetti from the University from Genoa, Italy, for their constructive comments on the occurrence of aluminosugilite, Thomas Armbruster for his constructive comments on the nomenclature ofwww.eur-j-mineral.net/32/57/2020/

M. Nagashima et al.: Aluminosugilite from the Cerchiara mine, Italy
milarite-group minerals, Yuzuru Maki (Rigaku Corporation) for his
arrangement to use RIGAKU HyPix-6000HE, Masahide Akasaka
for his permission on the use of Bruker APEX II installed at
Shimane University, and Yoji Morifuku for his technical assistance. We also thank the Editor-in-Chief Sergey Krivovichev, Christian L. Lengauer and an anonymous reviewer. One of the authors(Mariko Nagashima) gratefully acknowledge the financial supportsof Grants-in-Aid for Scientific Research from the Japan Society for
the Promotion of Science, nos. 285800296 and 18K03782.

Financial support. This research has been supported by the Grantsin-Aid for Scientific Research from the Japan Society for the Promotion of Science (grant nos. 285800296 and 18K03782).

Review statement. This paper was edited by Sergey Krivovichev,
and reviewed by Christian L. Lengauer and an anonymous reviewer.

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