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Demicheleite-(Cl), BiSCl, a new mineral from La Fossa crater, Vulcano, Aeolian Islands, Italy.
No full textDemicheleite-(Cl), ideally BiSCl, is the chlorine analog of demicheleite-(Br) and is closely related to this species that occurs in the same locality. The mineral is the first natural bismuth sulfochloride discovered so far in a natural environment, and it is identical with the corresponding and already known synthetic compound. It was found in an active medium-temperature intracrater fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. The mineral occurs as acicular to stout translucent crystals up to 0.25 mm long in an altered pyroclastic breccia, together with demicheleite-(Br), bismoclite, bismuthinite, godovikovite, panichiite, and three new minerals pending the IMA approval (IMA 2008-015, IMA 2008-039, and IMA 2008-057). The mineral is orthorhombic, space group Pnam, with a = 7.7933(10), b = 9.9293(12), and c = 3.9880(4) Å, V = 308.60(4) Å3 (from X-ray powder data), Z = 4. The crystal habit is prismatic with {110} as the dominant form, terminated by minor faces of another prism {011}, a pinacoid {010}, and a bipyramid {111}. The color is dark red to black; the luster submetallic. It is non-fluorescent. The tenacity is brittle. The cleavage and fracture were not observed. The calculated density is 5.934 g/cm3.
The chemical analysis obtained by WDS electron microprobe gave (wt%) Bi 72.74, Cl 11.42, Br 3.13, S 11.74, Se 0.01 wt%, total 99.04, corresponding to the empirical formula (based on 3 apfu): Bi0.97(Cl0.90Br0.11)Σ1.01S1.02.
The crystal structure has been refined to a final R index of 0.0218 and contains Bi in sevenfold coordination inside a monocapped trigonal prism. By base sharing, these polyhedra form rows extending
along [001]. The rows are connected with symmetry-related rows by sharing S-S edges of the pyramidal caps; these pairs of rows are linked to the others by sharing Cl/Br atoms. The distribution of bond lengths is close to that of the synthetic counterparts BiSCl and BiSBr, with Bi-S distances of 2.601(2) and 2.709(1) Å, and Bi-Cl/Br distances of 2.937(1) and 3.388(1) Å.
The strongest 6 lines in the X-ray powder diffraction pattern [dobs(Å) (I) (hkl)] are: 2.896 (100) (121), 4.174 (45) (120), 2.684 (42) (211), 2.784 (33) (201), 1.725 (30) (411), 2.543 (27) (031).
Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the IMA (no. 2008-020)
PANICHIITE, NATURAL AMMONIUM HEXACHLOROSTANNATE(IV), (NH4)2SnCl6, FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
No full textPanichiite, ammonium hexachlorostannate(IV), (NH4)2SnCl6, is a new mineral species found in a medium-temperature
intracrater fumarole (~250°C) at La Fossa crater, Vulcano Island, Aeolian Islands, Sicily, Italy. The mineral occurs as aggregates
of minute colorless octahedra up to 0.2 mm in diameter on fragments of altered pyroclastic breccia, in association with
alunite, anhydrite, bismuthinite, godovikovite, demicheleite-(Br) (BiSBr), BiSCl (IMA 2008–020) and two other new species,
a sodium ammonium aluminum sulfate chloride (IMA 2008–057) and an ammonium bismuth chloride that is presently under
study. Panichiite is cubic, space group Fm3m (no. 225), with Z = 4; the unit-cell parameter a is 10.064(1) Å, and V is equal to
1019.4(2) Å3. The X-ray powder-diffraction pattern is in excellent agreement with that of the synthetic compound; the strongest
six reflections [dobs in Å(I)(hkl)] are: 5.811(100)(111), 5.032(73)(200), 2.516(69)(400), 3.035(48)(311), 1.779(42)(440), and
2.250(39)(420). Chemical analyses obtained with an electron microprobe in energy-dispersion mode gave, on average, Cl 56.57,
Sn 31.62, Br 1.53, K 1.05, total 90.77, with NH4+ (by difference) 9.23, for a total of 100.00 wt.%, corresponding to the empirical
formula [(NH4)1.90K0.10]S2.00Sn0.99(Cl5.94Br0.07)S6.01. The calculated density for the compound with the above empirical formula
is 2.423 g/cm3. The index of refraction n obtained using immersion methods is 1.68(1) (l = 589 nm). The structure, including the
positions of the hydrogen atoms of the ammonium ion, was refined from single-crystal diffraction data to a final R of 0.030 for
153 independent observed reflections [I > 2s(I)]. The six equivalent Sn–Cl distances in the octahedral SnCl62– ion are 2.429(1)
Å, and the Cl...N distances are 3.559(1) Å. The mineral (IMA 2008–005) is named in honor of Prof. Ugo Panichi, a pioneer in
the study of minerals from Vulcano
BRONTESITE, (NH4)3PbCl5, A NEW PRODUCT OF FUMAROLIC ACTIVITY FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
No full textThe new mineral species brontesite, ammonium lead chloride (NH4)3PbCl5, was found in a medium-temperature (~250°C) active fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. The mineral occurs on a pyroclastic breccia as colorless to white tabular crystals up to 0.1 mm in length, in association with bismuthinite, godovikovite, demicheleite-(Cl), demicheleite-(Br), alunite, IMA 2008–057, (NH4)4NaAl2(SO4)4Cl(OH)2, and IMA 2009–049, BiSI. The mineral is orthorhombic, space group Pnma (no. 62), with Z = 4; the unit-cell parameters are: a 8.434(1), b 15.759(2), c 8.462(1) Å, V 1124.7(2) Å3. The strongest six reflections in the X-ray powder-diffraction pattern [dobs in Å(I)(hkl)] are: 3.067(100)(132), 2.020(80)(342), 2.710(78)(241), 1.910(78)(134), 2.421(75)(152) and 1.491(75)(373). Chemical analyses made with an electron microprobe in EDS mode gave, on average, Pb 47.8, Cl 36.1, Br 3.7, K 1.1, NH4 11.3 (by difference), for a total of 100.0 wt.%, corresponding to the empirical formula: [(NH4)2.87K0.13]S3.00Pb1.09(Cl4.79Br0.21)S5.00. The measured density is 2.72(1) g/cm3. The average index of refraction n is 1.70(3) (l = 589 nm). Using single-crystal diffraction data, the structure was refined to a final R = 0.0238 for 1463 independent observed reflections [I > 2s(I)]. The coordination polyhedron of the independent eight-coordinated Pb atom is a bicapped trigonal prism with Pb–Cl distances ranging from 2.777(1) to 3.724(1) Å. The Pb polyhedra are connected by sharing edges to form chains running along [100]. There are also two independent sites occupied by ammonium ions whose environment corresponds nearly exactly to that of the Rb atoms in Rb3PbCl5. It is essentially similar to that of the lead atom, i.e., the chlorine atoms are also arranged at the corners of bicapped trigonal prisms. There is some substitutional disorder involving the Pb2+ and NH4+ ions, similar to that occurring for Pb2+ and K+ in the high-temperature modification of KPb2Cl5. The mineral was approved as a new species by the IMA Commission on New Minerals, Nomenclature and Classification (IMA #2008–014); it is named after Brontes (Brnth), one of the three Cyclops (Knklvp) and a son of Uranus
Demicheleite-(I), BiSI, a new mineral from La Fossa Crater, Vulcano, Aeolian Islands, Italy
No full textDemicheleite-(I), ideally BiSI, is the iodine-dominant analogue of demicheleite-(Br) and demicheleite-
(Cl). It was found in an active medium-temperature intracrateric fumarole at La Fossa crater, Vulcano
Island, Aeolian archipelago, Sicily, Italy. The mineral is the first bismuth sulphoiodide so far
discovered in a wholly natural environment, and corresponds to the already known synthetic
compound. It occurs as acicular to stout, translucent crystals up to 0.25 mm long in an altered
pyroclastic breccia, together with demicheleite-(Br), bismoclite, bismuthinite, godovikovite, panichiite,
aiolosite, brontesite, adranosite and other new phases under study. The colour is dark red to black, the
lustre submetallic. The unit cell is orthorhombic, space group Pnam, with a = 8.4501(7) A ̊ , b =
10.1470(9) A ̊ , c = 4.1389(4) A ̊ , V = 354.88(4) A ̊ 3, and Z = 4. The crystal habit is prismatic, with the
main forms {110} and {111} inferred from analogy with demicheleite-(Br). Twinning was not
observed. The strongest 6 lines in the X-ray powder diffraction pattern [dobs.(A ̊ ) (I/I0) (hkl)] are: 6.490
(100) (110); 4.346 (94) (120); 3.896 (90) (210); 2.709 (60) (310); 2.161 (38) (330); 3.243 (22) (220).
The chemical analysis obtained by WDS electron microprobe gave: Bi 58.32, S 9.43, I 23.69, Br 5.66,
Cl 1.01, totalling 98.11 wt.%, corresponding to an empirical formula (based on 3 a.p.f.u.) of:
Bi0.97S1.03(I0.65Br0.25Cl0.10)S1.00. The unit-cell data are close to those of the synthetic compound, whose
crystal structure is already known. The calculated density is 6.411 g cm 3
THE CRYSTAL STRUCTURE OF CERVANDONITE-(Ce), AN INTERESTING EXAMPLE OF As3+ → Si DIADOCHY
No full textCervandonite-(Ce), a unique arsenosilicate from Alpine fissures at Pizzo Cervandone (Scherbadung) in the Central Alps between the Binn Valley (CH) and Ossola (I), has proven to be a problem in view of the extreme scarcity of single crystals suitable for the determination of its complex structure. The monoclinic supercell (Z = 6) originally described by the discoverers is
confirmed; we have established the crystal structure of a trigonal subcell, with space group R3m and a 6.508(1), c 18.520(3) Å, V 679.4(2) Å3 and Z = 3, to a final R(F) = 0.0380 for 441 observed independent reflections [I > 2s(I)]. The mechanism of the very unusual As3+ ! Si (not As5+ ! Si) diadochy is accounted for by considering the presence in two different sites of sorosilicate anions Si2O76–, which are statistically replaced by arsenite [AsO33–] anions and minor amounts of OH–; the positions of
the oxygen atoms common to these anions are the same. The asymmetric unit also contains one eight-coordinated atomic site occupied by Ce and other REE lying on the three-fold axis; a bipyramidal six-coordinated site (of symmetry .m) occupied by Fe, Ti, or Al also is present. The originally proposed chemical formula (Ce,Nd,La)(Fe3+,Fe2+,Ti4+,Al)3SiAs(Si,As)O13 is accordingly
revised to (Ce,Nd,La) Fe3+,Fe2+,Ti4+,Al)3O2(Si2O7)1–x+y (AsO3)1+x–y(OH)3x–3y, where x and y are 0.47 and 0.31, respectively, in the sample here examined
STEROPESITE, Tl3BiCl6, A NEW THALLIUM BISMUTH CHLORIDE FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
No full textSteropesite, Tl3BiCl6, a new thallium bismuth chloride, was found in an active high-temperature fumarole (~450°C) on the
rim at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. The mineral occurs as tabular or stout lemon-yellow crystals up
to 0.20 mm in length in association with bismuthinite and lafossaite. The mineral is monoclinic, space group Cc (no. 9), with
Z = 16; the unit-cell parameters are a 26.686(5), b 15.127(3), c 13.014(3) Å, b 108.11(2)°, and V 4993(2) Å3. The strongest six
reflections in the X-ray powder-diffraction pattern [dobs in Å(I)(hkl)] are: 3.773(100)(040), 2.113(93)(1200), 3.846(40)(332),
2.710(35)(442), 3.884(30)(402), and 2.745(30)(513). Chemical analyses obtained with an electron microprobe in wavelength
dispersion gave, on average, Tl 54.57, Bi 23.40, Cl 17.42, Br 4.13, Na 0.02, K 0.01, for a total of 99.55 wt.%, corresponding to
the empirical formula: (Tl2.89Na0.01)S2.90Bi1.21(Cl5.32Br0.56)S5.88. The calculated density for the compound with the above empirical
formula is 5.737 g/cm3. The average index of refraction n is 1.97(2) (l = 589 nm). The structure was refined from single-crystal
X-ray-diffraction data to a final R of 0.052 for 6232 independent observed reflections [I > 2s(I)]. The asymmetric unit contains
4 Bi, 12 Tl and 24 Cl atoms. The bismuth atoms display a distorted octahedral coordination, with Bi–Cl distances in the range
2.618–2.789 Å. Considering a maximum value of 3.6 Å for the Tl–Cl distances, five of the twelve independent Tl atoms are sixcoordinated
(Tl–Cl in the range 3.023–3.596 Å), six are seven-coordinated (Tl–Cl between 3.106 and 3.558 Å), and one is eightcoordinated
(Tl–Cl in the range 3.229–3.511 Å). The structure can be compared with those of other hexachlorobismuthates[III],
such as (NH4)3BiCl6, Cs3BiCl6 and CsK2BiCl6
Campostriniite, (Bi3+,Na)3(NH4,K)2Na2(SO4)6·H2O, a new sulfate isostructural with gorgeyite, from La Fossa Crater, Vulcano, Aeolian Islands, Italy
No full textThe new mineral campostriniite, (Bi3+,Na)3(NH4,K)2Na2(SO4)6·H2O, was found in an active fumarole
(fumarole FA, temperature ~350oC) at La Fossa Crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs
on a pyroclastic breccia as white prismatic crystals up to 0.2 mm long, in association with adranosite,
demicheleite-(Br), demicheleite-(I), argesite and sassolite. The mineral is monoclinic, space group: C2/c
(no. 15) with a = 17.748(3), b = 6.982(1) c = 18.221(3) A ̊ , b = 113.97(1)o, V = 2063(1) A ̊ 3 and Z = 4. The
six strongest reflections in the powder X-ray diffraction pattern are: [dobs in A ̊ (I)(hkl)] 6.396(100)(110),
7.507(75)(2 ̄ 02), 2.766(60)(3 ̄16), 3.380(57)(312), 5.677(55)(111), 3.166(50)(4 0 2). The empirical formula
(based on 25 anions p.f.u.) is Bi2.41N1.52Na2.41K0.48 S6.07H8.08O25. The calculated density is 3.87 g cm3.
Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.051 for 3025 independent
observed reflections [I > 2s(I)]. Campostriniite is isostructural with go ̈rgeyite and belongs to the 7.CD
group of the Strunz classification system. The structure contains two independent nine-fold coordinated
sites, one of them located on a two-fold axis (M1) and the other one in general position (M2) essentially
occupied by Bi3+ atoms and minor amounts of Na+ ions, an eight-fold coordinated site fully occupied by
Na+ ions and another eight-fold coordinated site occupied by NH4 + and K+ ions; three independent sulfate
anions in a general position and a water molecule coordinated to M1 and located on a two-fold axis are also present
Clinometaborite, natural beta-metaboric acid, from La Fossa crater, Vulcano, Aeolian islands, Italy
No full textClinometaborite, beta-HBO2, the monoclinic modification of metaboric acid, which has long been known as a synthetic product only, was found as a sublimate in an active medium-temperature intracrater fumarole at La Fossa crater, Vulcano Island, Aeolian archipelago, Sicily, Italy. It forms aggregates of stout crystals up to 2 mm long in an altered pyroclastic breccia, associated with metaborite, sassolite and adranosite. The unaltered mineral is colorless and translucent, with a vitreous luster; it becomes chalky white after some months of exposure to open air. The crystal habit is prismatic; twinning was not observed. The strongest six lines in the X-ray powder-diffraction pattern [dobs in Å(I)hkl] are: 3.078(100)201, 4.193(20)111, 6.773(15)001, 2.550(10)122, 3.224(8)201, and 2.702(8)031. The unit cell is monoclinic, space group P21/a, with a 7.127(2), b 8.842(3), c 6.773(2) Å, beta 93.21(1)°, V 426.1(2) Å3, Z = 12, values that virtually coincide with those of the synthetic compound. The calculated density is 2.049 g/cm3. The structure was refined to a final R of 0.043 for 977 observed reflections [I > 2sigma(I)]. Both the mineral and the mineral name have been approved by the IMA Commission on New Minerals, Nomenclature and Classification (IMA 2010–022)
PYRACMONITE, (NH4)3Fe(SO4)3, A NEW AMMONIUM IRON SULFATE FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
No full textThe new mineral species pyracmonite, ideally (NH4)3Fe(SO4)3, was found in a medium-temperature (~250°C) active intracrater fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as colorless to white prismatic crystals up to 0.2 mm in length, in association with salammoniac and kremersite. The mineral is trigonal, space group R3c (no. 161) with a 15.2171(14), c 8.9323(8) Å, V 1791.3(3) Å3 and Z = 6. The strongest six reflections in the X-ray powder-diffraction pattern [dobs in Å(I)(hkl)] are: 7.596(100)(110), 3.320(30)(122), 3.371(26)(131), 4.358(23)(121), 2.829(14)(312), and 2.863(8)(321). The empirical formula, based on 12 anions, is [(NH4)2.74K0.23]S2.97(Fe0.94Al0.04)S0.98S3.02O12, and the simplified formula (NH4,K)3(Fe,Al)(SO4)3. The measured density is 2.22(1) g/cm3, and Dcalc is 2.228 g/cm3. The mineral is uniaxial, and the average index of refraction index is 1.562(3) (l = 589 nm). Using single-crystal X-ray-diffraction data, the structure was refined to a final R(F) = 0.039 for 1010 independent observed reflections [I > 2s(I)]. The mineral is identical to the synthetic compound (NH4)3Fe(SO4)3 and is isostructural to the high-temperature phase of the synthetic compound (NH4)3In(SO4)3. Building blocks of the structure are (Fe,Al)O6 octahedra and SO4 tetrahedra, which are linked together to form infinite columns [(Fe,Al)(SO4)3]∞ along [001]. The two independent (Fe,Al)–O distances are 1.959(1) and 1.998(1) Å; in the sulfate anion, the S–O distances range from 1.415(2) to 1.485(1) Å. The ammonium ions, only partly replaced by K+ ions, interact with the oxygen atoms of the sulfate groups via hydrogen bonds
Argesite, (NH4)7Bi3Cl16, a new mineral from La Fossa Crater, Vulcano, Aeolian Islands, Italy : a first example of the [Bi2Cl10]4− anion
No full textThe new mineral argesite, ammonium bismuth chloride (NH4)7Bi3Cl16, was found in a medium-temperature (~250 °C) active fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. The mineral occurs on a pyroclastic breccia as pale-yellow crystals up to 0.15 mm in length, in association with bismuthinite, adranosite, brontesite, demicheleite-(Br), demicheleite-(Cl), and panichiite. Argesite is trigonal, space group: R3c (no. 167) with Z = 18; the unit-cell parameters are (single-crystal data): a = 13.093(1), c = 102.682(1) Å, and V = 15245(2) Å3. The six strongest reflections
in the X‐ray powder diffraction pattern are: [dobs(Å) (I) (hkl)] 3.164 (100) (0 3 18), 3.808 (44) (2 2 20), 2.742 (78) (2 4 21), 6.14 (16) (1 2 6), 1.906 (16) (0 0 54), 1.686 (13) (5 6 34). The mineral is uniaxial (–), with ω = 1.731(2), ε = 1.725(2) (589 nm). The IR spectrum shows absorptions at 3188(vs), 3060(s), and 1397(vs) cm–1, in agreement with the presence of the ammonium ion. Chemical analyses obtained by EDS electron microprobe gave (average wt%) Bi 42.26, Cl 32.57, Br 13.06, I 0.95, K 2.46, Tl 0.88, NH4 7.82 (by difference) total 100.00, corresponding to the empirical formula: [(NH4)6.29K0.91Tl0.06]Σ7.26Bi2.93(Cl13.33Br2.37I0.11)Σ15.81. The measured density is 2.88(1) g/cm3. The structure was refined, using single-crystal diffraction data, to a final R = 0.0345 for 1289 independent observed reflections [I > 2σ(I)]. It contains Bi2Cl104– and BiCl63– anions where the Bi atoms are octahedrally coordinated,
and NH4+ cations are partially replaced by K+ and Tl+ ions
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