62 research outputs found
Editorial for Special Issue “New Mineral Species and Their Crystal Structures”
Mineralogy is the oldest and one of the most important sciences of the geological cycle. Minerals,
the basis of overwhelming mass of solid matter in the universe, are direct subjects of investigation in
mineralogy. Minerals, or mineral species, are generally solid crystalline substances. Their definition
indicates that, they are: (1) naturally occurring; (2) belonging to the distinct structural type; (3) stable,
varying merely in the relatively small limits of chemical composition. If a given mineral differs from
other known species in its structure (2) and/or composition (3) then it can be considered as a new
mineral species[…
Raman imaging as a new approach to identification of the mayenite group minerals
The mayenite group includes minerals with common formula Ca12Al14O32−x(OH)3x[W6−3x], where W = F, Cl, OH, H2O and x = 0–2. This distinction in the composition is associated with W site which may remain unoccupied or be occupied by negatively charged ions: OH−, F−, Cl−, as well as neutral molecules like H2O. However, there is no experimental approach to easily detect or differentiate mineral species within the mayenite group. Electron micro-beam facilities with energy- or wavelength-dispersive X-ray detectors, as most common tools in mineralogy, appear to be insufficient and do not provide a definite identification, especially, of hydroxylated or hydrated phases. Some solution provides typical Raman analysis ensuring identification of minerals and 3D Raman imaging as an innovative approach to distinguish various co-existing minerals of the mayenite group within a small area of the rock sample. Raman spectroscopy has also been successfully used for a determination of water type incorporated into the mineral structure as well as for a spatial distribution of phases by cluster approach analysis and/or integrated intensity analysis of bands in the hydroxyl region. In this study, Raman technique was for the first time used to reconstruct a 3D model of mayenite group mineral zonation, as well as to determine a way of water incorporation in the structure of these minerals. Moreover, for the first time, Raman data were correlated with alterations during the mineral-forming processes and used for reconstruction of the thermal history of studied rock. As a result, the influence of combustion gases has been proposed as a crucial factor responsible for the transformation between fluormayenite and fluorkyuygenite
Kahlenbergite, a New Potassium β-Alumina Mineral : [abstract]
32nd European Crystallographic Meeting ECM 32, Vienna Austria, 18. – 23. 08. 201
Second occurrence of the new mineral harmunite CaFe2O4, Negev Desert, Israel.
Harmunite (ideally CaFe2O4) was found in the natural environment for the first time in 2014 in pyrometamorpic larnite rocks of the Hatrurim Complex that lies near Jabel Harmun – moutain located in Judean Desert, Israel - from which it derives its name (Galuskina et al. 2014). Macroscopically, together with srebrodolskite and magnesioferrite, harmunite creates black porous aggregates (Galuskina et al. 2014). In reflected light with crossed polars it has light gray colour with characteristic red internal reflections (Galuskina et al. 2014). Harmunite occurs as crystal faceted by the simple forms {100}, {110}, {210}, {011}, {001}, and {010} or as rounded fragments (Galuskina et al. 2014). The structure of CaFe2O4 consist of double rutile-type ∞1[Fe2O6] chains, which are further linked by common oxygen corners creating a tunnel-structure with large trigonal prismatic cavities occupied by Ca along [001] (Galuskina et al. 2014). Synthetic compound CaFe2O4 is known and used as ceramic material and pigment, semiconductors, refractories, thermally stable material and others (Candeia et al. 2004, Kharton et al. 2008). This phase was also previously found in the Salair pyrometamorphic complex of Kuznetsky coal basin in south – west Siberia, Russia (Nigmatulina & Nigmatulina 2009) and Chelabynsk coal basin, Southern Urals, Russia (Chesnokov et al, 1998) and described as “aciculite”, but it was not approved as a mineral due to its anthropogenic origin (Galuskina et al. 2014). We found harmunite in pyrometamorphic gehlenite rocks of the Hatrurim Complex located in north – east part of Negev Desert, Israel. As for the holotype specimen, it forms aggregates with srebrodolskite and Mg – ferrite. Single grains of harmunite from Negev reach about 25 μm in size. In comparison with holotype specimen, this harmunite contains more varied substitution at octahedral site , where Fe3+ is substituted by Cu, Ni or Zn. Futhermore, there is no Al, which was noted in holotype harmunite. The Raman spectrum of harmunite from Negev is similar to spectrum of holotype specimen and of the synthetic analog. The main Raman bands of harmunite from Negev are as follows (cm–1): 1241, 648, 601, 526, 439, 376, 301, 277, 214, 166, 131, 91
Walstromite, BaCa2(Si3O9), from Rankinite Paralava within Gehlenite Hornfels of the Hatrurim Basin, Negev Desert, Israel
Walstromite, BaCa2Si3O9, known only from metamorphic rocks of North America, was
found in small veins of unusual rankinite paralava within gehlenite hornfelses of the Hatrurim
Complex, Israel. It was detected at two localities—Gurim Anticline and Zuk Tamrur, Hatrurim
Basin, Negev Desert. The structure of Israeli walstromite [with P1
space group and cell parameters
a = 6.74874(10)Å, b = 9.62922(11) Å, c = 6.69994(12) Å, α = 69.6585(13)°, β = 102.3446(14)°, γ =
96.8782(11)°, Z = 2, V = 398.314(11) Å3) is analogous to the structure of walstromite from type
locality—Rush Creek, eastern Fresno County, California, USA. The Raman spectra of all tree
minerals exhibit bands related to stretching symmetric vibrations of Si-O-Si at 650–660 cm−1 and
Si-O at 960–990 cm−1 in three-membered rings (Si3O9)6−. This new genetic pyrometamorphic type of
walstromite forms out of the differentiated melt portions enriched in Ba, V, S, P, U, K, Na, Ti and F,
a residuum after crystallization of rock-forming minerals of the paralava (rankinite,
gehlenite-åkermanite-alumoåkermanite, schorlomite-andradite series and wollastonite).
Walstromite associates with other Ba-minerals, also products of the residual melt crystallization as
zadovite, BaCa6[(SiO4)(PO4)](PO4)2F and gurimite, Ba3(VO4)2. The genesis of unusual barium
mineralization in rankinite paralava is discussed. Walstromite is isostructural with
minerals—margarosanite, BaCa2Si3O9 and breyite, CaCa2(Si3O9), discovered in 2018
Not Only Garnets…
Garnets have been known to man since time immemorial and are used in a wide variety of applications as well as being prototypes of useful synthetic materials. Our investigations show that in nature, garnets and minerals with a langasite-type structure can be very close in composition. Examples are cubic Ti-rich garnets with the common formula Ca3(Ti4+,Fe3+,Al)2(Si,Fe3+,Al)3O12 and the new trigonal mineral qeltite, Ca3Ti(Fe3+2Si)Si2O14, which occur in paralavas of the pyrometamorphic Hatrurim Complex, Israel. Synthetic compounds of the langasite family are important because of their functional properties, such as unique piezoelectricity, high thermal stability, and low acoustic losses, as well as optical nonlinearity and multiferroicity. Qeltite is the first high-temperature terrestrial mineral with a langasite-type structure, the description of which was a catalyst for the discovery in pyrometamorphic rocks of the Hatrurim Complex of a whole series of new natural phases with langasite-type structure and varied composition (A3BC3D2O14, where A = Ca and Ba; B = Ti, Nb, Sb, and Zr; C = Ti, Al, Fe, and Si; and D = Si). We think that qeltite and other minerals with langasite-type structure may be relatively widely distributed in terrestrial rocks that form under similar conditions to those of Ti-rich garnet but are missed by researchers
Structural investigations on bredigite from the Hatrurim Complex
Bredigite, Сa7Mg(SiO4)4, is an indicator mineral of metasomatic rocks of the sanidinite facies formed at high temperatures
(>800 °C) and low pressures (<1–2 kbar). Bredigite samples from ternesite-gazeevite-larnite pyrometamorphic rocks of the
Hatrurim Complex (Negev Desert, Israel) have been studied by electron probe micro analysis and single-crystal diffraction using
synchrotron radiation. They are characterized by a relatively uniform composition. The empirical formula calculated on the basis
of 16 O atoms per formula unit is: (Ca7.006Na0.015Ba0.014)Σ7.035Mg0.938(Si4.000P0.014)Σ4.014O16. Basic crystallographic data of a
sample studied by X-ray diffraction are as follows: orthorhombic symmetry, space group Pnnm, a = 18.38102(17) Å, b =
6.74936(7) Å, c = 10.90328(11) Å, V = 1352.66(2) Å3, Z = 4. Structure solution and subsequent least-squares refinements
resulted in a residual of R(|F|) = 0.023 for 2584 independent observed reflections with I > 2σ(I) and 149 parameters. To the best
of our knowledge this is the first detailed structural investigation on natural bredigite. In contrast to previous studies on samples
retrieved from metallurgical slags there was no need to describe the structure in the acentric space group Pnn2. Furthermore, the
problem of Ba incorporation into the bredigite structure is discussed. Data on the composition of Ba-bearing bredigites from
pyrometamorphic rocks of the Hatrurim Complex from Jordan with simplified formula Ba0.7Ca13.3Mg2(SiO4)8 (based on 32
oxygen atoms) are provided for the first time, pointing out perspectives of finding new Ba-bearing minerals isostructural with
bredigite in nature
Molecular Hydrogen in Natural Mayenite
In the last 15 years, zeolite-like mayenite, Ca12Al14O33, has attracted significant attention
in material science for its variety of potential applications and for its simple composition.
Hydrogen plays a key role in processes of electride material synthesis from pristine mayenite:
{Ca12Al14O32}2+(O2)!{Ca12Al14O32}2+(e)2. Apresence of molecular hydrogen in synthetic mayenite
was not confirmed by the direct methods. Spectroscopy investigations of mayenite group mineral
fluorkyuygenite, with empirical formula (Ca12.09Na0.03)P
12.12(Al13.67Si0.12Fe3+
0.07Ti4+
0.01)P
12.87O31.96
[F2.02Cl0.02(H2O)3.22(H2S)0.15 0.59]P
6.00, show the presence of an unusual band at 4038 cm1, registered
for the first time and related to molecular hydrogen, apart from usual bands responding to vibrations
of mayenite framework. The band at 4038 cm1 corresponding to stretching vibrations of H2 is at
lower frequencies in comparison with positions of analogous bands of gaseous H2 (4156 cm1) and H2
adsorbed at active cation sites of zeolites (4050–4100 cm1). This points out relatively strong linking of
molecular hydrogen with the fluorkyuygenite framework. An appearance ofH2 in the fluorkyuyginite
with ideal formula Ca12Al14O32[(H2O)4F2], which formed after fluormayenite, Ca12Al14O32[ 4F2],
is connected with its genesis. Fluorkyuygenite was detected in gehlenite fragments within brecciaed
pyrometamorphic rock (Hatrurim Basin, Negev Desert, Israel), which contains reduced mineral
assemblage of the Fe-P-C system (native iron, schreibersite, barringerite, murashkoite, and cohenite).
The origin of phosphide-bearing associations is connected with the e ect of highly reduced gases on
earlier formed pyrometamorphic rocks
Chlorellestadite, Ca5(SiO4)1.5(SO4)1.5Cl, a new ellestadite- group mineral from the Shadil-Khokh volcano, South Ossetia
Acknowledgements This work was supported by grant no. 2015/17/N/ ST10/03141 (D. Ś.) from the National Science Centre (NCN) of Poland. Professor Pádhraig S. Kennan of University College at Dublin, Ireland, kindly helped with the English language. The authors are grateful to referee Professor S. Mills and Editor-in-Chief Dr. M.A.T.M. Broekmans for their constructive remarks, which greatly improved the original manuscript.Chlorellestadite (IMA2017–013), ideally Ca5(SiO4)1.5(SO4)1.5Cl, the Cl-end member of the ellestadite group was discovered in a calcium-silicate xenolith in rhyodacite lava from the Shadil Khokh volcano, Greater Caucasus, South Ossetia. Chlorellestadite forms white, tinged with blue or green, elongate crystals up to 0.2–0.3 mm in length. Associated minerals include spurrite, larnite, chlormayenite, rondorfite, srebrodolskite, jasmundite and oldhamite. The empirical crystal chemical formula of the holotype specimen is Ca4.99Na0.01(SiO4)1.51(SO4)1.46(PO4)0.03(Cl0.61OH0.21F0.11)Σ0.93. Unit-cell parameters of chlorellestadite are: P63/m, a = 9.6002(2), c = 6.8692(2) Å, V = 548.27(3)Å3, Z = 2. Chlorellestadite has a Mohs hardness of 4–4.5 and a calculated density of 3.091 g/cm3. The cleavage is indistinct, and the mineral shows irregular fracture. The Raman spectrum of chlorellestadite is similar to the spectra of other ellestadite group minerals, with main bands located at 267 cm−1 (Ca–O vibrations), and between 471 and 630 cm−1 (SiO4 4− and SO4 2− bending vibrations) and 850–1150 cm−1 (SiO4 4− and SO4 2− stretching modes). Chlorellestadite forms in xenoliths of calcium-silicate composition when they are exposed to Cl-bearing volcanic exhalations at about 1000 °C under low pressure conditions.NC
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