920 research outputs found
A low temperature X-ray single-crystal diffraction and polarised infra-red study of epidote
Full text linkThe effects of low-temperature on the crystal structure of a natural epidote [Ca1.925Fe0.745Al2.265Ti0.004 Si3.037O12(OH), a = 8.8924(7), b = 5.6214(3), c = 10.1547(6) angstrom and beta = 115.396(8)degrees at room conditions, Sp. Gr. P2(1)/m] have been investigated with a series of structure refinements down to 100 K on the basis of X-ray single-crystal diffraction data. The reflection conditions confirm that the space group is maintained within the T-range investigated. Structural refinements at all temperatures show the presence of Fe3+ at the octahedral M(3) site only [%Fe(M3) = 70.6(4)% at 295 K]. Only one independent proton site was located and two possible H-bonds occur, with O(10) as donor and O(4) and O(2) as acceptors. The H-bonding scheme is maintained down to 100 K and is supported by single crystal room-T polarised FTIR data. FTIR Spectra over the region 4,000-2,500 cm(-1) are dominated by the presence of a strongly pleochroic absorption feature which can be assigned to protonation of O(10)-O(4). Previously unobserved splitting of this absorption features is consistent with a NNN influence due to the presence of Al and Fe3+ on the nearby M(3) site. An additional relatively minor absorption feature in FTIR spectra can be tentatively assigned to protonation of O(10)-O(2). Low-T does not affect significantly the tetrahedral and octahedral bond distances and angles, even when distances are corrected for "rigid body motions". A more significant effect is observed for the bond distances of the distorted Ca(1)- and Ca(2)-polyhedra, especially when corrected for "non-correlated motion". The main low-T effect is observed on the vibrational regime of the atomic sites, and in particular for the two Ca-sites. A significant reduction of the magnitude of the thermal displacement ellipsoids, with a variation of U-eq (defined as one-third of the trace of the orthogonalised U-ij tensor) by similar to 40% is observed for the Ca-sites between 295 and 100 K. Within the same T-range, the U-eq of the octahedral and oxygen sites decrease similarly by similar to 35%, whereas those of the tetrahedral cations by similar to 22%.</p
Massive volcanic domes on Venus and the mobilisation of crystal mush: insights from the Troodos Ophiolite, Cyprus
No full textVenus is widely regarded as Earth’s ‘sister’ planet, given similarities in size, mass,
density, chemical composition, and also their proximity. However, there are also striking differences between the two planets. The surface of Venus is dominated by volcanic and tectonised volcanic terrains. Volcanism on Venus is, presumably, largely plume-related due to the absence of evidence for plate tectonic processes. Under the extreme high temperatures and pressures of the Venusian surface, lava flows can extend for hundreds to thousands of kilometres. Steep-sided domes are among the most starkly discernible volcanic landforms on the surface of Venus, given their gigantic size (e.g., 0.12–1.73 km in height, and 8.3–61.8 km in diameter) and peculiar shape, compared to other volcanic features. Those domes are believed to be volcanic edifices, characterised by steep margins, and relatively smooth, flat upper surfaces, exhibiting a circular shape in plan view. Given their distinct morphology, they are important in (1) understanding the range of magmatic processes operating on Venus, and (2)
elucidating geological evolution of planets lacking plate tectonics.
Despite their significance, there remains debate regarding the formation mechanisms of these domes. Physical models suggest that Venusian steep-sided domes require eruption of highly viscous liquids to explain their morphologies. This has led several authors to suggest that they represent eruption of SiO2-rich magmas at relatively low temperatures. However, other authors have argued that radar characteristics of steep-sided domes are inconsistent with eruption of very SiO₂-rich materials, and alternatively suggested that they represent eruption of more mafic liquids. In this scenario, high crystallinities may account for unusually high viscosities evidenced by dome morphology. Bulk viscosity of magmas depends on many factors, including composition (e.g., SiO₂ content and extent of polymerisation), volatile content, crystal content, and most importantly temperature. The overall aim of this study is to assess physical models of Venusian steep-sided dome formation by assessing the validity and implications of constraints on lava viscosity which they provide.
Work is divided into two Sections and four chapters. In Section 1 (Chapter 2), I model magma fractionation to calculate the full range of liquid compositions and bulk viscosity of magmas, which is compared to the viscosity thresholds from physical models. A key finding from this work is that high crystal contents are required to account for formation of high viscosity lavas on Venus. In Section 2 (Chapter 3 to 5), I conduct fieldwork to characterise a terrestrial analogue of eruption of high crystallinity picritic lavas in the Troodos Ophiolite, Cyprus. Using geochemical data, petrological and thermodynamic modelling, and field
observations, I investigate the formation and eruption mechanisms, parental magma compositions, and viscosities of picrites. Information from this section is then used to further assess steep-sided dome formation on Venus and controls of crystallinity on magma viscosity.
In Chapter 2, I implement thermodynamic modelling using the rhyolite-MELTS model to constrain magma compositions, and magma viscosities based on various viscosity parameterisations, using bulk compositions inferred from Venera 13 (alkaline basalt) and Venera 14 (low alkali basalt) Soviet lander data. Viscosities are then compared to viscosity thresholds from published physical models of Venusian dome formation. Extensive (>85–90%) fractional crystallisation or equilibrium melting processes alone fail to produce magmas with viscosities required to account for steep-sided domes. The presence of H₂O during equilibrium crystallisation substantially modifies magma composition (e.g., SiO₂), and decreases solidus temperature, contributing to an increase of liquid viscosity. However, this effect is less significant than the direct control of H₂O as a network modifier in lowering viscosity. Instead, our results reveal that crystal contents of >60 vol.% are invariably required to produce sufficiently high magma bulk viscosities. Such high crystallinities probably require eruption of crystal-rich magma followed by surface crystallisation, possibly enhanced by degassing and undercooling.
To further constrain the eruption mechanisms of high crystallinity magma, in Chapter 3, I conduct fieldwork to observe field relations and collect a suite of representative high crystallinity picritic bodies (e.g., lava flows and a dome) from the Margi (Mαρκί, sometimes referred to as Marki) region, Troodos Ophiolite, Cyprus. These picrites represent a series of mafic/ultramafic lava flows, with groundmasses ranging from glassy to holocrystalline/vitrophyric texture and typically containing variable, but very high concentrations of up to cm-sized olivine. The crystal content from different picrite bodies can vary from 36 to 66 vol.%. I describe field relations, petrology, and geochemistry of a number of these picrite bodies, including olivine (+spinel and melt inclusion) compositions, erupted glass compositions and whole rock data. These picrites are discrete units within the upper pillow lava sequence, with crystal contents that imply open-system crystal accumulation. Variations in composition and olivine crystal cargo imply that bodies have discrete compositions, and close proximity of picrites to extensional faults supports a model where extrusion of crystal mush onto the palaeo-seafloor was facilitated by rifting and tapping of small magmatic systems. However, olivine-spinel equilibration temperatures imply minimal re-equilibration, favouring a model of hot crystal mush storage in the crust.
In Chapter 4, based on olivine-hosted melt inclusion (MI) data, I use petrological modelling to constrain parental magma compositions, and petrogenesis of high crystallinity lavas. I also perform forward fractional crystallisation and partial melting using rhyolite-MELTS to constrain conditions under which olivine crystallisation occurred. Results are discussed within the framework of glass (e.g., erupted liquids), olivine and spinel compositional data. The key findings are (1) crystal-rich magmas are likely formed by magma recharging and repetitive fractionation and concentration of olivine crystals within magmatic systems at less than 0.4 GPa (i.e., ~15 km depth); (2) at least 40% of olivine phenocrysts within picrites are in equilibrium with liquids in which they have erupted, and that picrites are likely formed both by fractionation of olivine, and remobilisation of xenocrysts; (3) Erupted picrites represent a mixture of variably evolving melts (closed system fractionation) and olivine from a mush-rich magmatic system, with the average Fo content from different picritic bodies ranging between Fo₈₉ to Fo₉₁; (4) Parental magmas to both erupted liquids and olivines had variable compositions, including both variations in primary compositions and due to variable extents of sulfide saturation during early stages of olivine crystallisation.
In Chapter 5, I perform viscosity calculations based on glass compositions, H2O content, crystallinity, and crystal size distribution or morphology measured directly from picrite samples to estimate the viscosity of picritic flows and lavas in Margi. Although these lavas have very high crystal contents, calculated viscosities are relatively low due to the low viscosity of erupted liquids, which is, in turn, a function of mafic compositions, high water contents and high erupted temperatures. As a result, the picrite dome at Margi is not a good analogue for investigating the eruption mechanisms for Venusian domes, although picritic bodies at Margi do provide insight into the formation and eruptibility of high crystallinity magma. I further compile dome morphologies for all terrestrial lava domes from basaltic to rhyolitic compositions and other extra-terrestrial lava domes. Venusian steep-sided domes have a smaller aspect ratio (height/width) than 90% of terrestrial lava domes, indicating that direct
comparison between terrestrial domes and Venusian steep-sided domes is challenging given (1) their large difference in volumes and (2) the difference in surface environments between the two planets (e.g., surface temperature, pressure, atmosphere compositions, etc). As such, greater emphasis should instead be placed on improving models of dome formation under
Venusian conditions, and especially, on considering the key role of crystallinity, lava cooling rate as well as composition in controlling lava viscosity and dome morphology
Water incorporation in synthetic and natural MgAl2O4 spinel
Full text linkThe solubility and incorporation mechanisms of water in synthetic and natural MgAl2O4 spinel have been investigated in a series of high-pressure/temperature annealing experiments. In contrast to most other nominally anhydrous minerals, natural spinel appears to be completely anhydrous. On the other hand, non-stoichiometric Al-rich synthetic (defect) spinel can accommodate several hundred ppm water in the form of structurally-incorporated hydrogen. Infrared (IR) spectra of hydrated defect spinel contain one main O-H stretching band at 3343-3352 cm(-1) and a doublet consisting of two distinct O-H bands at 3505-3517 cm(-1) and 3557-3566 cm(-1). IR spectra and structural refinements based on single-crystal X-ray data are consistent with hydrogen incorporation in defect spinel onto both octahedral and tetrahedral O-O edges. Fine structure of O-H bands in IR spectra can be explained by partial coupling of interstitial hydrogen with cation vacancies, or by the effects of Mg-Al disorder on the tetrahedral site. The concentration of cation vacancies in defect spinel is a major control on hydrogen affinity. The commercial availability of large single crystals of defect spinel coupled with high water solubility and similarities in water incorporation mechanisms between hydrous defect spinel and hydrous ringwoodite (Mg2SiO4) suggests that synthetic defect spinel may be a useful low-pressure analogue material for investigating the causes and consequences of water incorporation in the lower part of Earth's mantle transition zone. (c) 2009 Elsevier Ltd. All rights reserved. <br/
Effects of temperature on the crystal structure of epidote: a neutron single-crystal diffraction study at 293 and 1070K
Full text linkThe effects of temperature on the crystal structure of a natural epidote [Ca-1.925 Fe0.745Al2.265Ti0.004Si3.037O12(OH), a = 8.890(6), b = 5.630(4), c = 10.150(6) and beta = 115.36(5)A degrees, Sp. Gr. P2(1) /m] have been investigated by means of neutron single-crystal diffraction at 293 and 1,070 K. At room conditions, the structural refinement confirms the presence of Fe3+ at the M-3 site [%Fe(M3) = 73.1(8)%] and all attempts to refine the amount of Fe at the M(1) site were unsuccessful. Only one independent proton site was located. Two possible hydrogen bonds, with O(2) and O(4) as acceptors [i.e. O(10)-H(1)center dot center dot center dot O(2) and O(10)-H(1)center dot center dot center dot O(4)], occur. However, the topological configuration of the bonds suggests that the O(10)-H(1)center dot center dot center dot O(4) is energetically more favourable, as H(1)center dot center dot center dot O(4) = 1.9731(28) , O(10)center dot center dot center dot O(4) = 2.9318(22) and O(10)-H(1)center dot center dot center dot O4 = 166.7(2)A degrees, whereas H(1)center dot center dot center dot O(2) = 2.5921(23) , O(10)center dot center dot center dot O(2) = 2.8221(17) and O(10)-H(1)center dot center dot center dot O2 = 93.3(1)A degrees. The O(10)-H(1) bond distance corrected for "riding motion" is 0.9943 . The diffraction data at 1,070 K show that epidote is stable within the T-range investigated, and that its crystallinity is maintained. A positive thermal expansion is observed along all the three crystallographic axes. At 1,070 K the structural refinement again shows that Fe3+ share the M(3) site along with Al3+ [%Fe(M3)(1,070K) = 74(2)%]. The refined amount of Fe3+ at the M(1) is not significant [%Fe(M1)(1,070K) = 1(2)%]. The tetrahedral and octahedral bond distances and angles show a slight distortion of the polyhedra at high-T, but a significant increase of the bond distances compared to those at room temperature is observed, especially for bond distances corrected for "rigid body motions". The high-T conditions also affect the inter-polyhedral configurations: the bridging angle Si(2)-O(9)-Si(1) of the Si2O7 group increases significantly with T. The high-T structure refinement shows that no dehydration effect occurs at least within the T-range investigated. The configuration of the H-bonding is basically maintained with temperature. However, the hydrogen bond strength changes at 1,070 K, as the O(10)center dot center dot center dot O(4) and H(1)center dot center dot center dot O(4) distances are slightly longer than those at 293 K. The anisotropic displacement parameters of the proton site are significantly larger than those at room condition. Reasons for the thermal stability of epidote up to 1,070 K observed in this study, the absence of dehydration and/or non-convergent ordering of Al and Fe3+ between different octahedral sites and/or convergent ordering on M(3) are discussed.</p
Crystal chemistry of accessory minerals as a probe of magmatic oxygen fugacity: an experimental study
Full text linkIt is well established that oxygen fugacity, fO₂ , is one of the key parameters that
needs to be quantified in order to understand igneous processes, model the geophysical
behaviour of the core and mantle, to understand the exchange of C-O-H-S gases between
the atmosphere and the interior of the Earth, and to further our understanding of
other terrestrial planets. Despite this it remains one of the most poorly constrained
geochemical variables, limiting our understanding of terrestrial systems. Recent work
has focused on using accessory minerals for determining magmatic fO₂ , as a probe to
constraining conditions in planetary interiors.
Accessory minerals are already important petrological tools for providing insight into
magmatic conditions. These minerals may concentrate a variety of trace elements, and
hence are crucial in understanding the elemental budget of magmas. Accessory minerals
such as zircon and apatite are also some of the hardier minerals found in igneous rocks
and are, therefore, less likely to be altered by processes such as chemical weathering,
metasomatism or crustal anatexis. Furthermore, study of detrital accessory minerals
in ancient sedimentary rocks could provide much needed insight into the evolution of
the oxidation state of the early Earth.
This work aims to assess how the compositions and structures of two accessory minerals,
spinel and apatite, respond to variations in magmatic fO₂ and to determine
whether these minerals could act as probes of fO₂ in planetary interiors. Focus has
been concentrated on the element manganese, as (1) it is a relatively abundant trace
element, (2) it can exist in valence states from Mn²⁺ to Mn⁵⁺ in nature, and (3) recent
work has suggested that Mn may become preferentially concentrated in apatite
under reduced conditions. In an initial investigation, large single crystals of Mn-rich
spinel were synthesised under a variety of fO₂ conditions. X-ray absorption near edge
structure (XANES) spectroscopy and structural refinements of single crystal X-ray
diffraction data were used to determine Mn valence state and coordination. Results
show that Mn is present in spinel as both Mn²⁺ and Mn³⁺, distributed over both octahedral
and tetrahedral cation sites. However, in contrast to the Fe⁺²/Fe³⁺ ratio, little
variation in Mn valence as a function of fO₂ was observed. Results were, however, useful
in testing and refining protocols for modelling Mn XANES data in a simple, model
system.
In contrast to results from spinel, previous studies have indicated that Mn valence may
change significantly in the accessory mineral apatite due to variations in magmatic fO₂ .
To test this, crystals of apatite in equilibrium with different silicate melt compositions
were synthesised at high pressure/temperature. Mn partitioning between apatite and
melt was determined by electron probe microanalysis (EPMA), and Mn valence state
determined by XANES spectroscopy. Although EPMA data revealed that there is no
dependence of Mn partitioning on fO₂ , it was noted that partitioning is dependent on
melt composition. In more silica-rich melts, a reduction in proportion of non-bridging
oxygen reduces the ability of melts to incorporate Mn. As such, apatite crystallising in
more evolved melts is expected to be enriched in Mn. These results are confirmed by
XANES data, which indicate that Mn is present in coexisting apatite and silicate melt
as Mn⁺⁻¹²³⁴⁵⁺², with no observed variation in Mn valence state with fO₂ .
In a final, preliminary investigation, attention was turned to Eu and Ce. Inferred variations
in the valence state of these rare earth elements, i.e. En²⁺/En³⁺ and Ce³⁺/Ce⁴⁺,
are already of use in petrological modelling. Two series of experiments were conducted
to synthesise Eu and Ce-bearing silicate glasses (both Fe-bearing and Fe-free) over a
range of fO₂ conditions, and apatite in equilibrium with various silicate melt compositions
at high pressure/temperature, again over a range of fO₂ conditions. XANES
characterisation of glasses demonstrates systematic variations in En²⁺/En³⁺ ratio with
fO₂ . In contrast, Ce is dominantly present in quenched glasses as Ce³⁺ under all fO₂
conditions. In apatite, there is little variation in En²⁺/En³⁺, with Eu dominantly incorporated
as En³⁺. Ce in apatite is dominantly incorporated as Ce³⁺. These results
indicate that apatite-melt partitioning of Eu should be dependent on fO₂ , potentially
providing a probe of magmatic fO₂ once the effects of melt compositions are constrained.
Results presented here highlight the potential use of apatite as a petrological indicator.
However, in contrast to previous work, I show that apatite-melt partitioning of Mn is
largely independent of fO₂ . In fact, observed trends in apatite chemistry previously
suggested to indicate variations in magmatic fO₂ can instead be fully explained by the
observed influence of melt structure/composition on Mn partitioning. In contrast, En
contents of apatite (for example apatite/whole rock ratios) may provide insight into
oxidation state in the deep Earth. However, more work is required to constrain the
influence of fO₂ on En (and other element) partitioning. Importantly, results here
highlight the important influence which melt structure has on element partitioning.
This control indicates that it is unlikely that fO₂ in the early Earth can be inferred
from the chemistry of detrital minerals in sedimentary rocks, or inherited minerals in
igneous/metamorphic rocks, as the composition of magmas from which these minerals
crystallised cannot easily be constrained
Manganese incorporation in synthetic hercynite
Full text linkManganese incorporation in synthetic hercynite, and partitioning between hercynite and silicate melt synthesized at 1.0 GPa, 1250°C, and at an f O2 buffered by Fe–FeO, has been studied by X-ray absorption spectroscopy and single-crystal X-ray structure refinement. Spectra indicate the presence of both Mn2+ and Mn3+ (and possibly also Mn4+) in synthetic hercynite and partitioning of Mn2+ into the melt phase, and Mn3+ into hercynite, respectively, under run conditions. X-ray refinement is consistent with partial disorder of Fe and Al across tetrahedral and octahedral sites. A higher than expected degree of Fe-Al disorder in the Mn-bearing hercynite can be explained by preferential incorporation of Mn2+ onto the tetrahedral site, and indicates that Fe-Al disorder in pure, stoichiometric hercynite cannot necessarily be used to determine closure temperatures in natural spinel. However, partitioning of Mn2+ and Mn3+ between melt and hercynite suggests that Mn incorporation in hercynite could be used as a measure of f O2 conditions in magmas during spinel crystallization
Was Weber Wrong? A Human Capital Theory of Protestant Economic History: A Comment on Becker and Woessmann
Full text linkThis comment makes a contribution to Becker and Woessmann’s paper on a human capital theory of Protestant economic history eventually challenging the famous thesis by Max Weber who attributed economic success to a specific Protestant work ethic (Quarterly Journal of Economics 124 (2) (2009) forthcoming). The authors argue for a human capital approach: higher literacy among Protestants of the 19th century (and not a Protestant work ethic) contributed to higher economic prosperity at that point in history. However, the paper leaves the question open as to whether a Protestant specific work ethic existed or exists at all. Are there observable denomination-based differences in work ethic or is Protestantism only a veil hiding the underlying role of education? We use recent data to explore the role of Protestantism on work ethic. The results indicate that today’s work ethic in fact is influenced by denomination-based religiosity and also education.Religion, Work Ethic, Protestantism, Education
Raman Spectroscopy and Forensic Mineralogy
No full textRaman Spectroscopy is a non-destructive technique which provides detailed information about chemical structure, phase and polymorph, crystallinity and molecular interactions. It is a light scattering technique, in which a molecule scatters incident light from a high intensity laser light source. A Raman spectrum features a number of peaks, showing the intensity and wavelength position of the Raman scattered light. Each peak corresponds to a specific molecular bond vibration, including individual and groups of bonds. Typically, a Raman spectrum is a distinct chemical fingerprint for a particular molecule or material, and can be used to readily identify the material, or distinguish it from others, especially with the use of modern spectral libraries. Raman spectroscopy can be used to analyse many different materials, including solids, powders, liquids, gels, slurries and gases, inorganic, organic and biological materials, pure chemicals, mixtures and solutions. For these reasons, Raman techniques are used increasingly in forensic science fields to characterise gemstones, pigments, explosives and some dangerous materials
Solid solutions along the synthetic LiAlSi2O6 (spodumene)-LiFeSi2O6 (ferri-spodumene) join: a general picture of solid solutions, bond lengths, lattice strains, steric effects, symmetries and chemical compositions of Li clinopyroexenes
Full text linkSeven clinopyroxene compositions along the joinM2LiM1AlTSi2O6(spodumene) toM2LiM1Fe3+TSi2O6(ferri-spodumene) were synthesized at 2 GPa, 800 °C under highly oxidizing conditions (using H2O2fluid) in an end-loaded piston cylinder. In addition, the LiFe3+TSi2O6composition was also synthesized under the intrinsically reducing conditions in a piston cylinder, to check the effect of fO2 on iron speciation. The run products were characterized by field emission scanning electron microscope (FE-SEM), Rietveld refinements on XRPD synchrotron data, and space groups were assigned using SAED-TEM patterns. Run products are composed mainly of lithium clinopyroxene (Li-Cpx), plus minor amounts of hematite (magnetite under reducing condition) and corundum, as independently detected by image analysis (area%) and Rietveld refinements (wt%); moreover, Rietveld results were used to derive cell parameters, M1-site occupancy (Al vs. Fe3+), atomic positions, and average bond lengths of all these Li-Cpx indexed in the C2/c space groups according to SAED-TEM. Li-Cpx with Al and Fe3+amounts close to 50:50 are actually slightly richer in Al apfu than nominal; the LiFe3+Si2O6grown under very oxidized and reducing conditions have very similar cell parameters, indicating that fO2 is unable to induce a significant incorporation of Fe2+ in these Li-Cpx. The replacement of Al with Fe3+induces a linear (%) increase of the cell edges following b ≥ a > c, whereas β is roughly constant and the cell volume increases linearly. Furthermore, the substitution of Al with Fe3+ only weakly affects the T-O average length ( b > a > c, whereas ? is roughly constant except for Ti-end-member and P21/c compositions. Lattice strains induced by X, T, and P for Li-Cpx in the C2/c stability field show that when the M1 site is progressively filled with a large cation, ε1 axis (ε1ε2ε3) increases along b, whereas ε2and ε3are nearly parallel to a and at about 30° from c. Conversely, T will provoke a similar enlargement of ε1and ε2along b and a edges, respectively, whereas ε3is again oriented at about 30° from c; the increasing of P will instead shorten all strain tensor components (ε1, ε2, and ε3) with a similar percentage amount; notably, high-P is the only stress that induces a strain component to be almost parallel to c edge. Moreover, finite lattice strains and orientation in C2/c LiMe3+Si2O6Li-Cpx induced by Me3+: Al-Fe3+, Fe3+-Sc, Sc-In are slightly different, with &1 invariably lying along b; conversely, Li-Na cation substitution is completely different with the highest and lowest deformations on the ac plane and ε2along b; ε3vector is negative and oriented at about 30° from T-chains. The ideal replacement of Al with larger cations up to In in Li-Cpx induces the M1-O, M2-O, and T-O average bond lengths to increase by 10.6, 4.3, and <0.5%. Steric effects in LiM1Me3+Si2O6and NaM1Me3+Si2O6 Cpx are significant and very similar, whereas several other Me1+and Me2+substitutions in Cpx at both the M1 and M2 site, keeping fixed the other site, display less or even the absence of steric effects. Our new data also better elucidate relationships between Li-Cpx composition, symmetry at room and non-Ambient conditions and Tc. The aggregate cation radii at the M1 site does not exclusively control the stability of C2/c and P21/c polymorphs; instead valence electrons can profoundly favor the stabilization of a polymorph
- …
