Zoharite, (Ba,K)₆ (Fe,Cu,Ni)₂₅S₂₇, and Gmalimite, K₆□Fe²⁺₂₄S₂₇—New Djerfisherite Group Minerals from Gehlenite-Wollastonite Paralava, Hatrurim Complex, Israel

Abstract

Zoharite (IMA 2017-049), (Ba,K)₆ (Fe,Cu,Ni)₂₅S₂₇, and gmalimite (IMA 2019-007), ideally K₆□Fe²⁺₂₄S₂₇, are two new sulfides of the djerfisherite group. They were discovered in an unusual gehlenite–wollastonite paralava with pyrrhotite nodules located in the Hatrurim pyrometamorphic complex, Negev Desert, Israel. Zoharite and gmalimite build grained aggregates confined to the peripheric parts of pyrrhotite nodules, where they associate with pentlandite, chalcopyrite, chalcocite, digenite, covellite, millerite, heazlewoodite, pyrite and rudashevskyite. The occurrence and associated minerals indicate that zoharite and gmalimite were formed at temperatures below 800 °C, when sulfides formed on external zones of the nodules have been reacting with residual silicate melt (paralava) locally enriched in Ba and K. Macroscopically, both minerals are bronze in color and have a dark-gray streak and metallic luster. They are brittle and have a conchoidal fracture. In reflected light, both minerals are optically isotropic and exhibit gray color with an olive tinge. The reflectance values for zoharite and gmalimite, respectively, at the standard COM wavelengths are: 22.2% and 21.5% at 470 nm, 25.1% and 24.6% at 546 nm, 26.3% and 25.9% at 589 nm, as well as 27.7% and 26.3% at 650 nm. The average hardness for zoharite and for gmalimite is approximately 3.5 of the Mohs hardness. Both minerals are isostructural with owensite, (Ba,Pb)₆(Cu,Fe,Ni)₂₅S₂₇. They crystallize in cubic space group Pm$\overline{3}$m with the unit-cell parameters a = 10.3137(1) Å for zoharite and a = 10.3486(1) Å for gmalimite. The calculated densities are 4.49 g·cm⁻³ for the zoharite and 3.79 g·cm⁻³ for the gmalimite. The primary structural units of these minerals are M₈S₁₄ clusters, composed of MS₄ tetrahedra surrounding a central MS₆ octahedron. The M site is occupied by transition metals such as Fe, Cu, and Ni. These clusters are further connected via the edges of the MS₄ tetrahedra, forming a close-packed cubic framework. The channels within this framework are filled by anion-centered polyhedra: SBa₉ in zoharite and SK₉ in gmalimite, respectively. In the M₈S₁₄ clusters, the M atoms are positioned so closely that their d orbitals can overlap, allowing the formation of metal–metal bonds. As a result, the transition metals in these clusters often adopt electron configurations that reflect additional electron density from their local bonding environment, similar to what is observed in pentlandite. Due to the presence of shared electrons in these metal–metal bonds, assigning fixed oxidation states—such as Fe²⁺/Fe³⁺ or Cu⁺/Cu²⁺—becomes challenging. Moreover, modeling the distribution of mixed-valence cations (Fe²⁺/³⁺, Cu⁺/²⁺, and Ni²⁺) across the two distinct M sites—one located in the MS₆ octahedron and the other in the MS₄ tetrahedra—often results in ambiguous outcomes. Consequently, it is difficult to define an idealized end-member formula for these minerals.

1. Introduction

Two new sulfides, zoharite, Ba₆Fe²⁺(Fe²⁺₁₆Cu⁺₈)S₂₇, and gmalimite, K₆□Fe²⁺₂₄S₂₇, belong to the djerfisherite group along with the following minerals: djerfisherite K₆(Fe,Cu,Ni)₂₅S₂₆Cl [1], thalfenisite Tl₆(Fe,Ni)₂₅S₂₆Cl [2] and owensite (Ba,Pb)₆(Cu¹⁺,Fe,Ni)₂₅S₂₇ [3,4].

Djerfisherite was described in 1966 from the enstatite chondrite Kota-Kota, Malawi [1]. In 1969, Genkin and co-authors described the first terrestrial djerfisherite from the sulfide ore of the Talnakh deposit, Russia [5]. Later, djerfisherite and its Cl-free analog were described as accessory minerals in numerous terrestrial rocks including kimberlites [6,7,8,9,10], dunites, peridotites and gabbro [11,12,13], carbonatites [14], and high-temperature contact metamorphic rocks [13,15]. Thalfenisite, Tl₆(Fe,Ni)₂₅S₂₆Cl the thallium analog of djerfisherite, was found in pentlandite-galena-chalcopyrite ores of the Oktyabrsky Cu-Ni deposit, Norilsk, Russia, localized at the contact of chalcopyrite and galena, and included in pentlandite [2]. Barkov et al. [16,17] described a series of minerals with composition between Cl-free thalfenisite (potentially a new mineral) and gmalimite from ores of the Oktyabrsky Cu-Ni deposit, Norilsk, Russia. The first owensite (Ba,Pb)₆(Cu¹⁺,Fe,Ni)₂₅S₂₇ was found within samples containing disseminated sulfides in peridotite and pegmatitic gabbro in the Wellgreen Cu-Ni-Fe-Pd deposit from the West Zone of the Quill Creek Ultramafic Complex, Yukon, Canada [3,4].

Zoharite is the second barium sulfide, and an Fe-analog owensite. Owensite and minerals of the zoharite-gmalimite series were reported from metacarbonate xenolith from alkali basalt of Bellerberg volcano, Eifel, Germany [12]. A potentially new mineral a Cu-analog of gmalimite from xenoliths of the Pian di Celle volcano, Italy, were described by Sharygin [18]. Recently, zoharite and owensite have been found in pyrometamorphic rocks in Mongolia [19]. Gmalimite is the chlorine-free analog of djerfisherite, K₆(Fe,Cu,Ni)₂₅S₂₆Cl, and it the eighth natural potassium sulfide after djerfisherite [1], rasvumite, KFe₂S₃ [20], bartonite, K₆Fe₂₀S₂₆S [21], murunskite, K₂(Cu,Fe)₄S₄ [22], chlorbartonite, K₆Fe₂₄S₂₆(Cl,S) [23] and colimaite, K₃VS₄ [24].

Both minerals and their names, zoharite (IMA 2017-049) and gmalimite (IMA 2019-007), have been approved by the IMA Commission on New Minerals, Nomenclature and Classification (CNMNC). The names are derived from the geographic name—Mt. Zohar, which overtops the Hatrurim Basin and Wadi Gmalim—a tributary of Wadi Hemar, also in the Hatrurim Basin (Figure 1). Holotype specimens of zoharite and gmalimite are deposited in the mineralogical collection of the Fersman Mineralogical Museum, Moscow, Russia under catalog numbers 4959/1 and 5297/1, respectively.

Currently, the determination of end-member formulas for minerals of the djerfisherite group remains a complex and unresolved issue. This challenge arises primarily from the difficulty in accurately establishing the valence states of Cu and Fe due to metal–metal bonding (e.g., Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺), particularly when these metals occupy mixed-cation sites. In this study, we present a comprehensive characterization of newly identified djerfisherite-group minerals and discuss the complexities inherent in defining their end-member compositions.

2. Materials and Methods

The morphology and composition of the new sulfides were studied using a light microscope, a Phenom XL tabletop scanning electron microscope, ThermoFisher Scientific, Eindhoven, The Netherlands, and a CAMECA SX100 electron microprobe analyzer, CAMECA, Gennevilliers, France. Several series of electron probe microanalyses (EPMA) were performed at 15 kV, 20 nA, beam diameter ~1 μm, using the following lines and standards: NaKα—albite; K Kα—orthoclase; Ba Lα—baryte; FeKα—chalcopyrite, pentlandite; CuKα—chalcopyrite; NiKα—pentlandite, NiO; SKα—pentlandite, chalcopyrite; SeKα—Bi₂Se₃. Pb, Co, Rb, Tl, Zn, As, Mn, Cl, P, Si, Al, Ca are below detection limit.

The Raman spectra of zoharite and gmalimite were recorded using a WITec alpha 300R confocal Raman microscope, WITec, Ulm, Germany, equipped with an air-cooled 532 nm solid-state laser and a CCD camera operating at −61 °C. The laser beam was coupled to the microscope via a 3.5 μm diameter single mode optical fiber. An air Zeiss LD EC Epiplan–Neofluan DIC objective (100/0.75NA) was used. The Raman scattered light was focused by a broadband single mode fiber with an effective Pinhole size of approximately 30 μm and a monochromator with an 1800 mm⁻¹ grating. The laser power on the sample was ~1–2 mW. Integration times of 20 s with an accumulation of 60 scans were chosen. The resolution is about 2 cm⁻¹. The monochromator was calibrated using the Raman scattering line of a silicon plate (520.7 cm⁻¹). The spectra were processed using the GRAMS Spectracalc software package, version 9.2, and the Raman bands were fitted using a Gauss–Lorentz cross-product function.

Single-crystal X-ray studies were performed with synchrotron radiation, λ = 0.70849 Å. Diffraction experiments at ambient conditions were performed at the X06DA beamline of the Swiss Light Source (Paul Scherrer Institute, Villigen, Switzerland). For experiments, the in-house-developed DA+ acquisition software was used [27]. Determination of lattice parameters was performed using CrysAlisPro 171.42.70a [28]), data reduction and absorption corrections were processed with XDS [29]. Crystal structure refinement was performed using SHELX97 [30], “Supplementary Materials”. Experimental details and refinement data are summarized in

Table 1. Details of data collection and structure refinement of gmalimite and zoharite.

Mineral	Gmalimite	Zoharite
Refined formula	(K5.05 Ba0.04□0.91) Σ6(Fe0.39□0.61) Σ1 (Fe15.31Cu5.76 Ni2.93)Σ24S27	(Ba3.91K2.09)(Fe0.97□0.03)Σ1 (Fe15.1Cu6.5□2.4)Σ24 S27
Crystal system	cubic
Unit cell dimensions (Å)	a = b = c = 10.34863(8) α = β = γ = 90°	a = b = c = 10.3137(1) α = β = γ = 90°
Space group	$\mathit{Pm}\overline{3}$m (no. 221)
Volume (Å3)	1108.28(3)	1097.09(3)
Z	1
Density (calculated) g/cm3	3.720	4.227
Crystal size (μm)	50 × 40 × 20	50 × 40 × 40
	Data collection
Diffractometer	beamline X06DA, Swiss Light Source
	SLS one-axis goniometer Aerotech	multi-axis goniometer PRIGo
	λ = 0.70849 Å
Detector/det. distance	PILATUS 2M-F/80 mm
Exposure time (s)/step size (°)	0.1/0.1
Number of frames	1800
Max. θ range for data collection (°)	33.28	31.92
Index ranges	−15 ≤ h ≤ 15	−10 ≤ h ≤ 11
	−14 ≤ k ≤ 14	−14 ≤ k ≤ 8
	−15 ≤ l ≤ 16	−15 ≤ l ≤ 15
No. of measured reflections,I > 2\σ(I)	4636	6508
No. of unique reflections,I > 2\σ(I)	428	436
	Refinement of the structure
no. of parameters	24	24
Rint	0.0397	0.0112
R1(obs)/R1(all)	0.0364/0.0408	0.0122/0.0123
wR2(obs)/wR2(all)	0.0974/0.1020	0.0286/0.0286
GOF	1.22	1.193
Δρ min. (e Å−3)	−1.74 (1.75 Å from S4)	−0.50 from S3
Δρ max. (e Å−3)	1.85 (0.38 Å from S1)	0.30 from S2

.

3. Occurrence

Zoharite and gmalimite were discovered in an unusual gehlenite–wollastonite paralava with pyrrhotite nodules located in the Hatrurim pyrometamorphic complex, Negev Desert, Israel.

Pyrometamorphic rocks of the Hatrurim Complex, represented by spurrite marbles, gehlenite hornfelses and larnite pseudoconglomerates, are widely distributed along the Dead Sea Rift [25,26,31,32,33]. However, paralavas with different chemical/mineralogical composition can be found in just a few localities. In the Hatrurim Basin, the largest area of pyrometamorphic rocks of the Hatrurim Complex in Israel, two types of paralavas are most prevailing. The first type is gehlenite–schorlomite–wollastonite paralava that fills small, up to 5 cm thick veins in yellow-brown gehlenite hornfelses [34,35]. This type of paralava is the metamorphic equivalent of the chalky-marly sequence of the Ghareb Formation (Maastrichtian). Another dominant type is yellow-green gehlenite–wollastonite paralava containing pyroxene of the diopside–esseneite series and anorthite [32,36]. Fe³⁺-bearing minerals as hematite, magnesioferrite, gorerite, and khesinite are widespread in the mineral association of these paralavas and enclosing hornfelses [37]. This type of paralava belong to the so-called ‘olive’ unit, which is the metamorphic equivalent of the marly–clayey sequence of the Taqiye Fm (Paleocene). ‘Olive’ units are commonly located at top of the hills in the northern part of the Hatrurim Basin. They form outcrops of tens, rarer hundreds of square meters [26,32].

In addition to more common types, an unusual amygdaloidal gray gehlenite–wollastonite basalt-like paralava enriched in pyrrhotite was revealed in the southern part of the Hatrurim Basin in the wadi Halamish (N31°09′42″ E35°17′29″) (Figure 1). Relatively large outcrops show rocks with disseminated pyrrhotite mineralization and rare sulfide nodules, up to 2 cm in size (Figure 2 and Figure 3).

In the gehlenite-rich outcrops, several lenses of gray paralava were found in the Wadi and as tops on small hills. Sizes of the lenses range from one to several tens of meters, with thickness up to a few meters. Stratigraphically, these paralava belongs to the lower part of the pyrometamorphic sequence of the Hatrurim Complex (Ghareb Fm is protolith), just a few meters above the upper sedimentary phosphorite layer (Mishash Fm, Campanian). The paralava lenses and gehlenite-rich outcrops are embedded in low-temperature hydrothermally altered rocks composed mainly of carbonates, zeolites and calcium hydrosilicates. The major and minor minerals of gray paralava are wollastonite, gehlenite, fluorapatite, pyrrhotite, and also feldspars (celsian, anorthite and orthoclase) (Figure 2D). Pentlandite, perovskite, Ti-Al-bearing uvarovite, spinel of the chromite–spinel–magnetite series, cuspidine, rankinite, kalsilite and hematite after pyrrhotite are accessory and rare minerals of gray paralava. Idiomorphic crystals of kirschsteinite often form at the boundary with sulfide nodules (Figure 3D). Secondary, low–temperature minerals as thomsonite–Ca, gismondine–Ca, phillipsite–Ca, willhendersonite, but also ettringite–thaumasite series, tacharanite, goethite, baryte–celestine series and gypsum can fill amygdules of paralava and may also replace primary Ca–silicates and sulfides. All these phases were identified by microprobe analysis and Raman spectroscopy.

Zoharite and gmalimite occur at the boundary of sulfide nodules with gray paralava (Figure 2B, Figure 3 and Figure 4). Sulfide nodules (globules) usually contain an asymmetric cavity separated from the paralava by a thin sulfide rim, which is intensely replaced by hematite and goethite. This cavity is partially or completely filled with zeolites, calcite, baryte and minerals of the tobermorite group. The sulfide nodules consist of pyrrhotite with pentlandite inclusions (Figure 3A,B). Depending on the cross-sectional direction—along the massive nodule or fragment of the nodule with a cavity—it appears as massive pyrrhotite globules, quite often with a manifestation of chalcopyrite zone (Figure 3A) or sulfide crust at the contact with the host rock paralava (Figure 4A).

Typically, the sulfide nodule consists of a few large pyrrhotite crystals, as indicated by the direction of cleavage cracks in these crystals. In reflected light, the pyrrhotite shows patchy twinning indicating the transformation of primary high-temperature Ni-bearing monosulfide melt to pyrrhotite, accompanied by small droplets of pentlandite exsolution (Figure 3B). Zoharite and gmalimite are always associated with chalcopyrite at the periphery of the globules (Figure 3A–C). Gmalimite replaces chalcopyrite and is overgrown by zoharite (Figure 3B,C). Small zoharite crystals also occur at the boundary between the sulfide nodule and the paralava with kirschsteinite (Figure 3D). Besides pyrrhotite and pentlandite, further minerals such as chalcocite, digenite, covellite, millerite, heazlewoodite, pyrite, and rudashevskyite are noted in association with minerals of the djerfisherite group.

Zoharite and gmalimite form irregular grained aggregates up to 100 μm in size (Figure 3C and Figure 4B,D). The color of both minerals is bronze with dark-gray streak. They are opaque minerals with a metallic luster. In reflected light zoharite and gmalimite are gray with an olive tinge. When the minerals are touched, it can be seen that zoharite has a weaker green hue than gmalimite and slightly higher reflectivity (

Table 2. Reflectance values of zoharite and gmalimite.

λ (nm)	Zoharite R (%)	Gmalimite R (%)	λ (nm)	Zoharite R (%)	Gmalimite R (%)
400	18.5	17.9	560	25.4	25.1
410	18.8	17.9	570	25.7	25.5
420	19.1	18.1	580	26.0	25.6
430	19.5	18.7	589 (COM)	26.3	25.9
440	19.9	18.9	590	26.3	26.0
450	21.0	19.9	600	26.7	26.0
460	21.3	20.9	610	26.8	26.0
470 (COM)	22.2	21.5	620	27.1	26.1
480	22.5	22.0	630	27.1	26.1
490	22.8	22.4	640	27.6	26.1
500	23.3	22.9	650 (COM)	27.7	26.3
510	23.6	23.4	660	27.7	26.4
520	24.2	23.7	670	27.6	26.3
530	24.4	24.1	680	27.7	26.2
540	24.8	24.4	690	27.8	26.1
546 (COM)	25.1	24.6	700	27.9	26.2
550	25.2	24.8

notes: λ—wavelength; R—reflectance value; COM—four wavelengths recommended by the COM (the Commission on Ore Mineralogy).

). The mean microindentation hardness is 172.9 kg/mm², range 156.8–186.4 kg/mm², at VHN load 50 g for zoharite and 190(6) kg/mm², range 179–201 kg/mm², at VHN load 25 g for gmalimite. The Mohs scale hardness of zoharite and gmalimite is similar, around 3.5. Cleavage and parting are not observed. Tenacity is brittle and sectile. Fracture of both minerals is irregular, partly conchoidal. Density could not be measured because of intergrowth with other sulfides and the small size of the pure crystal fragments extracted, the calculated density is 4.49 g·cm⁻³ for zoharite and 3.79 g·cm⁻³ for gmalimite obtained on the basis of the empirical formula and unit cell volume refined from single-crystal XRD data.

The chemical formulae of the holotype zoharite, calculated on the basis of average analyses is (Ba_3.81K_1.80Na_0.22□_0.17)_Σ6(Fe_14.21Cu_5.45Ni_3.27□_2.07)_Σ25(S_26.94Se_0.06)_Σ25. From the aggregate shown in Figure 3C, a grain was extracted for the structural investigation, a single-crystal XRD analysis. The chemical formulae of the holotype gmalimite, calculated on the basis of average analyses for the grain used for the structural investigation is (K_4.97Ba_0.02□_1.01)_Σ6(Fe_16.61Cu_5.78Ni_2.93□_0.32)_Σ25S₂₇, where the aggregate shown in Figure 4D has a slightly different average formula (K_5.02Ba_0.03□_0.95)_Σ6(Fe_17.01Cu_5.11Ni_3.32)_Σ25.32S₂₇. In order for the formulae obtained to be charge neutral, some of the Cu should be monovalent (

Table 3. Chemical composition of gmalimite (1—grain used for SCXRD, 2—aggregate, Figure 4B) and zoharite (3—aggregate, Figure 3C).

	1	2			3
wt.%	n = 3	n = 13	s.d.	range	n = 14	s.d.	range
S	33.77	33.58	0.36	32.74–34.06	30.87	0.63	29.92–32.07
Se	n.d.	n.d.			0.17	0.05	0.08–0.27
K	7.58	7.61	0.24	7.39–8.36	2.51	0.08	2.33–2.63
Ba	0.12	0.14	0.08	0–0.30	18.68	0.60	17.00–19.52
Na	n.d.	n.d.			0.18	0.05	0.08–0.33
Fe	36.19	36.84	1.27	34.48–38.85	28.35	1.43	24.85–30.98
Ni	6.71	7.56	1.22	6.25–10.28	6.85	0.97	4.01–8.95
Cu	14.33	12.58	2.50	7.51–15.43	12.38	2.62	8.05–17.78
Total	98.70	98.32			99.99
Calculated on cations and normalized on 27(S + Se)
K	4.97	5.02			1.80
Ba	0.02	0.03			3.81
Na					0.22
□	1.01	0.95			0.17
A	6.00	6.00			6.00
Fe2+	16.61	17.01			14.21
Ni	2.93	3.32			3.27
Cu	5.78	5.11			5.45
□	-				2.07
M + M’	25.32	25.44			25.00
S	27.00	27.00			26.94
Se					0.06
X + Y	27.00	27.00			27.00
Cation charge (Cu2+)	55.65	55.96			55.50
Cation charge (Cu+)	49.87	50.85			50.05

). An accurate calculation of monovalent Cu content cannot be made as the Fe²⁺/Fe³⁺ ratio in these minerals is unknown. Zoharite and gmalimite are characterized by a high degree of chemical inhomogeneity even within a single grain and have significant variations in Cu and Ni contents (Table 3).

Our recent investigation has shown that the minerals of the djerfisherite group from sulfide nodules of the gehlenite-wollastonite paralava of Wadi Halamish exhibit by a wide variety. In addition to zoharite and gmalimite, Ba-bearing djerfisherite, K-bearing high-Fe owensite, and a potentially new mineral—an Ni-analog of owensite have been identified (Figure 5).

4. Raman Spectroscopy Study of Zoharite and Gmalimite

The Raman spectra of zoharite and gmalimite are similar and resemble the spectra obtained for djerfisherite [9,38]. There are four bands in the spectra (zoharite/gmalimite, respectively, cm⁻¹): 105/101, 144/136, 267/268 and 336/341 (Figure 6). It is estimated that bands 267/268 and 336/341 cm⁻¹ are related to symmetric stretching vibrations of Fe-S, while bands 105/101 and 144/136 cm⁻¹ are related to bending vibrations of S-Fe-S in tetrahedral and octahedral sites, respectively [38].

5. Crystal Structure of Zoharite and Gmalimite

The crystal structure refinement of zoharite and gmalimite, was started with the model of isostructural owensite, (Ba,Pb)₆(Cu,Fe,Ni)₂₅S₂₇ [4], where Pb or (Ba, Pb) was replaced by K. Details of the data collection and structure refinement of gmalimite and zoharite are given in Table 1. Atom coordinates, isotropic and anisotropic displacement parameters and site occupancies for zoharite and gmalimite are in

Table 4. (a) Atomic coordinates and equivalent isotropic displacement parameters (Ų) for gmalimite. K1 and Fe2 show mixed occupancy. (b) Atomic coordinates, U_iso (Ų) values for zoharite.

(a)
Site	x	y	z	Uiso	Occupancy
K1	0	0	0.2954(2)	0.0406(6)	(a) 0.842(3)K + 0.006(3)Ba + 0.281□
Fe1	0.5	0.5	0.5	0.0340(18)	(b) 0.387(11)Fe + 0.613□
Fe2	0.36849(3)	0.36849(3)	0.13333(4)	0.0261(2)	(c) 0.638 Fe + 0.24 Cu + 0.122 Ni
S1	0	0	0	0.0449(10)	1S
S2	0.24863(10)	0.50	0	0.0244(3)	1S
S3	0.5	0.5	0.25487(14)	0.0241(3)	1S
S4	0.23025(8)	0.23025(8)	0.23025(8)	0.0275(3)	1S
(a) occupancy parameters of K and Ba are refined to matching a total scattering of 16 electrons. (b) occupancy parameter of Fe1 is refined to matching a total scattering of 10 electrons. (c) occupancy parameters of Fe, Cu, and Ni are set to matching chemical analysis and total scattering of the site.
(b)
Site	x	y	z	Uiso	Occupancy
Ba1/K1	0	0	0.30022(2)	0.01716(8)	0.652(2) Ba + 0.348(2) K
Fe1	0.5	0.5	0.5	0.0153(2)	(a) 0.97 Fe + 0.03 □
Fe2/Cu2	0.36685(2)	0.36685(2)	0.13604(2)	0.0181(2)	(b) 0.628(2) Fe + 0.27 Cu + 0.102□
S1	0	0	0	0.0184(3)	1S
S2	0.24794(5)	0.50	0	0.01621(12)	1S
S3	0.5	0.5	0.25988(7)	0.01587(15)	1S
S4	0.22326(4)	0.22326(4)	0.22326(4)	0.01912(14)	1S
(a) total scattering on this site equals 25 electrons. (b) total scattering on this site equals 24 electrons.

,

Table 5. (a) Anisotropic displacement parameters U_ij for gmalimite. (b) Anisotropic displacement parameters U_ij for zoharite.

(a)
Site	U11	U22	U33	U12	U13	U23
K1	0.0368(7)	0.0368(7)	0.0483(11)	0	0	0
Fe1	0.0340(18)	0.0340(18)	0.0340(18)	0	0	0
Fe2	0.0258(2)	0.0258(2)	0.0267(3)	−0.00051(9)	−0.00051(9)	0.00026(12)
S1	0.0449(10)	0.0449(10)	0.0449(10)	0	0	0
S2	0.0229(4)	0.0261(4)	0.0241(4)	0	0	0
S3	0.0250(4)	0.0250(4)	0.0221(5)	0	0	0
S4	0.0275(3)	0.0275(3)	0.0275(3)	0.0027(3)	0.0027(3)	0.0027(3)
(b)
Atom	U11	U22	U33	U23	U13	U12
Ba1	0.01774(9)	0.01774(9)	0.01600(12)	0	0	0
Fe1	0.0153(2)	0.0153(2)	0.0153(2)	0	0	0
Fe2	0.0172(4)	0.0172(4)	0.0200(3)	−0.00057(18)	−0.00057(18)	0.00000(15)
S1	0.0184(3)	0.0184(3)	0.0184(3)	0	0	0
S2	0.0157(2)	0.0160(2)	0.0169(2)	0	0	0
S3	0.0166(2)	0.0166(2)	0.0144(3)	0	0	0
S4	0.01912(14)	0.01912(14)	0.01912(14)	0.00231(14)	0.00231(14)	0.00231(14)

and

Table 6. Selected interatomic distances (Å) and bond valence sums (BVS) for zoharite and gmalimite, calculated using ECoN21 [39], all Fe as Fe²⁺ and all Cu as Cu²⁺.

Zoharite			Gmalimite
Site 1	Site 2	Bond Lengths (Å)	Site 1	Site 2	Bond Lengths (å)
Ba1/K1 (Ba0.652(2)K0.348(2))	-S1	3.0964(2)	K1 (K0.842(3)Ba0.006(3)□0.281)	-S1	3.057(2)
	-S2	3.2840(4) ×4		-S2	3.333(2) × 4
	-S4	3.3517(5) × 4		-S4	3.436(1) × 4
	mean	3.293(1)		mean	3.348(1)
	BVS	1.94		BVS	1.05
Fe1(Fe0.97□0.03)	-S3	2.4765(7) × 6	Fe1 (Fe0.387(11) □0.613)	-S3	2.537(1) × 6
	BVS	2.25		BVS	0.76
Fe2/Cu2 (Fe0.629(2)Cu0.27□0.102)	-S4	2.2794(4)	Fe2 (Fe0.638Cu0.240Ni0.122)	-S4	2.258(1)
	-S2	2.3149(3) × 2		-S2	2.301(1) × 2
	-S3	2.3244(5)		-S3	2.299(1)
	mean	2.308		mean	2.290(1)
	BVS	2.03		BVS	2.29
S1	Ba1/K1	3.0964(2) × 6	S1	K1	3.057(2) × 6
	BVS	2.15		BVS	1.45
S2	Ba1/K1	3.2840(4) × 2	S2	K1	3.333(2) × 2
	Fe2/Cu2	2.3149(3) × 4		Fe2	2.301(1) × 4
	mean	2.638		mean	2.645
	BVS	2.43		BVS	2.45
S3	Fe1	2.4765(7) × 4	S3	Fe1	2.537(1) × 4
	Fe2/Cu2	2.3244(5)		Fe2	2.299(1)
	mean	2.446		mean	2.4894
	BVS	2.32		BVS	2.36
S4	Ba1/K1	3.3517(5) × 3	S4	K1	3.436(1) × 3
	Fe2/Cu2	2.2794(4) × 3		Fe2	2.258(1) × 3
	mean	2.816		mean	2.847
	BVS	2.19		BVS	2.13

. Selected interatomic distances (Å) and bond valence sums (BVS) for zoharite and gmalimite, calculated using ECoN21 [39], all Fe as Fe²⁺ and all Cu as Cu²⁺.

Gmalimite and zoharite crystallize in the cubic space group Pm$\overline{3}$m. The main building units of their structures are M₈S₁₄ clusters formed by MS₄ tetrahedra, where M = Fe, Cu and Ni. Via the edges of the tetrahedra, the clusters are further connected to a cubic close-packed framework (Figure 7A). At the center of the clusters are cation-centered MS₆ octahedra (Figure 7C,D). The large cavities between the clusters host anion-centered octahedra SBa₆ in zoharite or SK₆ in gmalimite (Figure 7A) or, according to the other interpretation, contain Ba/K polyhedral columns (Figure 7B).

In the structure of zoharite and gmalimite, Ba and K are bonded to nine S atoms in the form of a monocapped square antiprism (Figure 7E). The lower base of the antiprism is formed by four S2 atoms, with distances of 3.284(1)/3.333(2) Å to Ba/K. The larger upper square base is defined by four S4 atoms, with longer distances of 3.352(1)/3.436(1) Å to Ba/K. This base is topped with the ninth sulfur atom (S1) with a bond length of 3.0964(3)/3.057 to Ba/K.

Occupancy factors at the Ba/K site for zoharite have been refined to 65% Ba (3.9 apfu) and 35% K (2.1 apfu), which corresponds to the microprobe data analyses (Table 3). Moreover, microprobe analysis Table 3) indicates that significant part of this site in gmalimite is vacant. The occupational parameters of K and Ba for gmalimite are refined by summing up to a total scattering of 16 electrons ≈ 85% obtained by population refinement for K. Therefore, a total occupation is fixed at 0.106 (out of 0.125), and for this value the occupation refinement converged to 0.842(3) for K and 0.0006(3) for Ba, corresponding to (5.05 apfu) for K and (0.004 apfu) for Ba in chemical formula.

In the M₈S₁₄ clusters in gmalimite and zoharite, Fe (26 electons), Cu (29 electrons) and Ni (28 electrons) atoms and some vacancies share one octahedral M1S₆ and one tetrahedral position M2S₄. Modeling a proper distribution of Fe, Cu, and Ni over these two sites are hindered by two additional factors. The scattering power of Ni and Cu is very close for X-rays. The valence state of iron and copper is unknown. Associated minerals from this area show that Fe²⁺ and Fe³⁺, as well as Cu¹⁺ and Cu²⁺ are possible, so any preferences for tetrahedral or octahedral coordination cannot be considered. Therefore, the population of these two sites has been refined using ‘dummy atomic scattering factors’, representing a mixture of Fe, Cu, Ni atoms and vacancies. The first mixed site labeled Fe1 is coordinated by six S3 atoms and forms a regular octahedron with bond lengths of 2.476(1) Å (zoharite) and 2.537(1) (gmalimite). A second mixed site, Fe2 (4₂-fold), is coordinated by four S to form a disordered tetrahedron with bond lengths between 2.279(1) and 2.324(1) (zoharite) and 2.258(1) and 2.299(1) (gmalimite).

The refinement of the zoharite population converged to 0.97 Fe (~25 electrons) for an atom on the Fe1 site and to 0.94 Fe (24 electrons) for the 24 atoms on the Fe2 site. These values can be calculated as the sum of 25 electrons for the octahedral site and 24 electrons on the tetrahedral site. The average electron microprobe analysis for the same sample yielded Fe²⁺ 14.21 p.f.u. which correspond to 369.5 electrons. Thus, the neutral atoms substituting for Fe on both sites, have an average atomic number of (601 − 369.5)/(25 − 14.21) = 21.5 which is less than Cu (29) or Ni (28). Consequently, additional vacancies have to be incorporated into the structure. This is also in agreement with microprobe analysis (Table 3). Therefore, Fe1 site was refined and fixed to (Fe0.97□0.03). At the tetrahedral site, Cu2 was restrained to 0.27 (≈ 6.5 atoms), and the occupation parameter of Fe2 was refined. The refined chemical formula of zoharite is (Ba_3.91K_2.09)(Fe_0.97□_0.03) (Fe_15.1Cu_6.5□_2.4) _Σ24S₂₇.

Population refinement of gmalimite accounts for about 10 electrons at Fe1 site. This suggests, that a large part of the Fe1 site is vacant. Modeling substitutional displacement of three atoms on such a low occupancy (occ. ≈ 0.39) is not meaningful; therefore, only a small amount of Fe is refined there (Table 4a). Consequently, Cu and Ni were placed on the tetrahedral site, with fixed occupancies corresponding to the results of the microprobe analysis (Cu_5.76Ni_2.93) and the rest of the position is filled with Fe_15.29 atoms. The total number of electrons, obtained from this arrangement is 27, which fits the refined dummy atom population. The refined chemical formula of gmalimite is (K_5.05 Ba_0.04□_0.91)_Σ6 (Fe_0.39□_0.61) _Σ1(Fe_15.31Cu_5.76 Ni_2.93)_Σ24S₂₇.

The calculated values of the BVS (Table 6), show expected values. In zoharite, the BVS values for a nine-coordinated Ba1/K1 site with refined composition (Ba_0.652(2)K_0.348(2)) is slightly overbonded with 1.94 valence units (v.u.). The six-coordinated Fe on a Fe1 site is slightly overbonded with bvs of 2.25 v.u., while the four coordinated Fe and Cu atoms at Fe2/Cu2 site show an average bvs of 2.03 v.u. (calculated for Fe²⁺ and Cu²⁺). If some of these atoms are Fe³⁺ and Cu¹⁺, an average bvs remains close to 2. All sulfur atoms in zoharite are slightly overbonded with bvs values ranging from 2.15 v.u. (for S1) to 2.43 v.u. (for S2). The S2 atom is coordinated to two Ba/K atoms and four Fe/Cu of Fe2 site. If the Fe2/Cu2 site would contains only Fe³⁺ and Cu⁺ instead, the bvs for S2 decreases slightly to 2.31 valence units.

In gmalimite, the Fe atom at the Fe1 site has a BVS of 0.76 (1.97 for full occupation) v.u., while the metal atoms at the Fe2 site (Fe_0.638Cu_0.240Ni_0.112) show an average BVS of 2.29 v.u. (assuming Fe²⁺ and Cu²⁺). The S2, S3, and S4 atoms in gmalimite are also slightly overbonded. The highest value is observed for the six-coordinated S2 atom (2.45 v.u.), which forms four bonds to metals at the Fe2 (Fe, Cu) site. Assuming a change in oxidation states—Fe²⁺ to Fe³⁺ and Cu²⁺ to Cu⁺—would slightly reduce this BVS to 2.4 v.u. The only sulfur atom in gmalimite with a lower BVS is S1 (1.45 v.u.). This is due to its longer average bond length to six K atoms (3.0570(3) Å), which is 0.12 Å longer than the predicted 2.936 Å. As a result, the effective coordination number for S1 is five, rather than six.

X-ray powder diffraction data were not collected, but were calculated from the results of single-crystal structure refinements, as gmalimite and zoharite occur only in tiny amounts. The calculated data are provided in

Table 7. Calculated powder pattern for zoharite and gmalimite. Intensities were calculated using the software Jana2006 [40] up to d = 0.7 Å and 5% threshold.

Zoharite					Gmalimite
dhkl [Å]	Iref [%]	h	k	l	dhkl [Å]	Iref [%]	h	k	l
10.3218	10	0	0	1	10.3567	91	0	0	1
7.2986	6	1	0	1	7.3233	33	1	0	1
5.9593	12	1	1	1	5.9795	59	1	1	1
3.4406	15	2	1	2	3.4522	9	0	0	3
3.4406	25	0	0	3	3.2751	28	1	0	3
3.264	65	1	0	3	3.1227	56	1	1	3
3.1121	45	1	1	3	2.9897	58	2	2	2
2.9796	80	2	2	2	2.5892	6	0	0	4
2.8628	9	2	0	3	2.5119	11	1	0	4
2.5034	14	1	0	4	2.376	51	3	1	3
2.368	66	3	1	3	2.0713	11	3	0	4
2.308	9	2	0	4	2.0311	6	3	1	4
2.2524	10	2	1	4	1.9932	11	1	1	5
1.9864	21	1	1	5	1.9932	6	3	3	3
1.9167	7	2	0	5	1.8308	100	4	0	4
1.8845	6	2	1	5	1.8029	5	4	1	4
1.8247	100	4	0	4	1.7762	6	3	3	4
1.7702	17	3	3	4	1.7506	9	3	1	5
1.7203	8	0	0	6	1.5613	12	2	2	6
1.5561	13	2	2	6	1.4502	5	1	1	7
1.5387	7	4	2	5	1.3483	7	3	1	7
1.5387	7	3	0	6	1.2946	10	0	0	8
1.5219	5	3	1	6	1.2653	7	3	3	7
1.3553	10	3	0	7	1.1368	4	5	3	7
1.2902	10	0	0	8	1.057	14	4	4	8
1.261	13	3	3	7	0.9154	4	8	0	8
1.2517	5	4	4	6	0.8188	8	4	0	12
1.0535	12	4	4	8	0.7741	14	7	3	11
0.9584	7	4	0	10	0.7719	14	8	4	10

.

6. Discussion

6.1. Comments on Crystal Chemistry of Minerals of the Djerfisherite Group

Minerals of the djerfisherite group usually have unbalanced empirical formulas by charge with a predominance of positive charge on cations. In some cases, the formula can be ‘additionally’ balanced by the changing the valence of Cu from 2+ to 1+ or/and by inserting a vacancy at this position. This approach was used to calculated to end-member formula of gmalimite K₆□Fe²⁺₂₄S₂₇. After a consultation with the chairman of the CNMNC-IMA (2019), end-member formula for zoharite Ba₆Fe²⁺(Fe²⁺₁₆Cu⁺₈)S₂₇ was proposed. Finally, the simplified formula for zoharite (Ba,K)₆ (Fe,Cu,Ni)₂₅S₂₇ was approved by the CNMNC-IMA.

Synthetic analogs of djerfisherite, K₆Fe₂₅S₂₆Cl [38], and zoharite, Ba₆Fe₂₅S₂₇ [41], as well as isostructural Ba₆Ni₂₅S₂₇ [42] and Ba₆Co₂₅S₂₇ [43], show charge-imbalanced formulas of 56+/53− and 62+/54−, respectively. A similar issue with unbalanced end-member formula is known for minerals of pentlandite and bartonite groups, where as in the minerals of the djerfisherite group, the M₈S₁₄ clusters are the main structural elements (Figure 7A and Figure 8A). For example, approved formula for chlorbartonite is K₆Fe²⁺₂₄S₂₆Cl (54+/53−), and for cobaltpentlandite Co₉S₈ (18+/16−).

The solution of the end-member formula problem of the djerfisherite group minerals and structurally related minerals of the bartonite and pentlandite groups is related to their structural peculiarities, connected with M₈S₁₄ clusters (Figure 8). The M₈S₁₄ clusters are usually presented with formula M₈(μ4-S)₆S₈, where M is a metal, (μ₄-S) means that each sulfur bridges four metal atoms and a six of (μ₄-S) form the core of an octahedral cluster, and outer eight S atoms are terminal ligands or bridging to two metals. Such a cluster is shown in Figure 8A, where eight metal atoms (Fe, Ni, Co) are placed at the corners of a cube, whose edges are ~2.6–2.8 Å in length and sulfur atoms either capping faces or bridging. In these clusters metals are close enough to share electrons directly with each other, by overlap of d orbitals and form metal-metal bond. Since the bond is shared equally, each metal “gets” one electron from it. However, due to the metal–metal bonds, transition metal sulfides (as in pentlandite, (Fe,Ni)₉S₈) often do adopt electron configurations that approximate 18-electron arrangements in their local bonding environments, even when sulfur gives only 16 electrons (i.e., [41,42]).

We propose to consider minerals of the djerfisherite, as well as bartonite and pentlandite groups as a special case, where the principle of the formula electroneutrality does not have to be realized in the calculation using the standard valence of elements. We believe that formulas of gmalimite and zoharite should be simplified to K₆Fe₂₅S₂₇ and Ba₆Fe₂₅S₂₇. A few years ago, we sent to the CNMNC-IMA a proposal concerning to the classification of the minerals of the djerfisherite group taking into account the arguments mentioned above. The approval of this proposal is still in process. Taking into account the CNMNC-IMA rules, which state that the paper on a new mineral should be published within the three years from its approval, we decided to publish the data on gmalimite and zoharite with the officially approved by the CNMNC-IMA formulas, and leave the elaboration of the classification of the minerals of the djerfisherite group to the next generation of the mineralogists.

6.2. Comments on Genesis

The unusual gehlenite–wollastonite paralavas of the Hatrurim Complex may be a model object for the studying the mechanism of sulfide globules formation processes in natural silicate melt systems. At present we have limited data to discuss this issue. In general, it should be noted that the genesis of zoharite and gmalimite is related to the liquation processes, when sulfide liquid droplets are separated in silicate melt at temperatures higher than 1100 °C [44]. The crystallization of this liquid within 850–1100 °C starts with the formation of Ni enriched monosulfide solid solution (MSS) [45], which later transforms into pyrrhotite with pentlandite aggregates (Figure 3A). The formation of MSS is accompanied by the separation of Cu-enriched residual liquid (ISS—intermediate solid solution), whose crystallization product (mainly, chalcopyrite) forms outer zones of sulfide nodules or is dispersed in the near-contact zone with paralava (Figure 3A). Reaction of ISS with interstitial residual silicate melt locally enriched in Ba and K leads to formation of sulfides of the djerfisherite group at temperature < 800 °C.