A century of mineral structures: How well do we know them?

Angel, R. J.; Nestola, Fabrizio

doi:10.2138/am-2016-5473

Cited by 29 publications

(24 citation statements)

References 82 publications

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“…This R int is similar to that achieved from olivine crystals measured in air (e.g. [17]), providing an additional indication that the corrections made by frame-scaling are precise. The structure refined to the full data set, collected to 100° 2θ (resolution 0.46 Å) and averaged in the Laue group mmm, is reported in the deposited crystallographic information file with key results given in the first column of Table 1.…”

Section: Resultssupporting

confidence: 81%

“…Both the statistical measures of fit, and the ESDs on bond lengths and angles are similar to those from olivine crystals measured in air to the same resolution (e.g. [17]). Olivine inclusions in diamonds normally contain trace ( < 1% total cations) amounts of Mn, Ni and Ca [19].…”

Section: Resultssupporting

confidence: 56%

“…sites in the olivine structure, the 'electron in bond' model [16,17] was used. This includes a single electron placed along the Si-O bonds to model the bonding electron density, in combination with fullyionized scattering factors for the cations, and half-ionized scattering factors for the oxygen atoms.…”

Section: Methodsmentioning

confidence: 99%

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High-quality structures at high pressure? Insights from inclusions in diamonds

Angel

Milani

Alvaro

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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We describe the experimental protocols necessary to measure the crystal structures of minerals trapped within diamonds by single-crystal X-ray diffraction to the same quality as obtained from minerals studied at ambient conditions. The results show that corrections for X-ray absorption in complex cases can be made with good precision. Comparison of the refined structure of a single-crystal olivine inclusion inside a diamond with the structure of a similar olivine held in a high-pressure diamond-anvil cell shows that data resolution, not the correction for absorption effects, is the dominant factor in influencing the quality of structures determined at high pressures by single-crystal X-ray diffraction.

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Section: Resultssupporting

confidence: 81%

Section: Resultssupporting

confidence: 56%

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High-quality structures at high pressure? Insights from inclusions in diamonds

Angel

Milani

Alvaro

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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“…In terms of other key physical‐property investigations of minerals, it is standard practice to continually make new and better measurements with increased accuracy and precision. For example, the crystal structures of many rock‐forming minerals have been refined via diffraction investigations a number of times (see Angel & Nestola, ). Indeed, they note that experimental diffraction measurements have become so quantitative over time that it is now the refinement procedure itself that determines the accuracy of a crystal structure and not the raw experimental data.…”

Section: Brief Backgroundmentioning

confidence: 99%

Recent developments and the future of low‐T calorimetric investigations in the Earth sciences: Consequences for thermodynamic calculations and databases

Geiger

Dachs

2018

Journal Metamorphic Geology

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Low-T calorimetry is an experimental science that measures the thermodynamic function heat capacity, C p (T), from which the standard third-law entropy (298.15 K), S°, is calculated. The recent technological development of relaxation calorimetry allows both new experimental strategies and types of C p investigations to be made, which were previously not possible. The C p measurements are fast and automated and can be made on mg-sized mineralogical samples between 2 and 400 K. These advantages, when careful measurement procedures are used, permit better determinations of C p (T) behaviour. The C p of synthetic single-crystal MgO was measured between 5 and 302 K, and S°calculated using relaxation calorimetry to further investigate the method's precision and accuracy. A number of synthetic and natural end-member or nearly end-member compositions of silicate garnet were investigated in the past via adiabatic calorimetry, an old and established technique, and more recently and extensively with the relaxation method. First C p (T) and S°results, using relaxation calorimetry, have been obtained on spessartine (Mn O 12 ), often on multiple samples, have resolved uncertainties and certain problems with published thermodynamic data. S°can be affected by various low-T physical phenomena, such as cooperative magnetic phase transitions or Schottky anomalies at temperatures of <15 K, which were not described fully in some older adiabatic calorimetric studies. New C p results show that small differences in the thermodynamic behaviour between some natural and synthetic silicates may exist as demonstrated by extensive work on grossular. Important and "new" research questions on the thermodynamic behaviour of minerals are coming to light and are being investigated. The C p behaviour and S°values for six silicate garnet end-members are analysed and the latter are compared to the "best fit or optimized" S°values given in various internally consistent thermodynamic databases. Conclusions are drawn on what types and directions of calorimetric study are required in order to obtain better thermodynamic property determinations of minerals, as well as achieving a better understanding of the underlying microscopic physical behaviour that determines the macroscopic C p and S°functions.

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“…The instrument is equipped with a Mo micro-focus X-ray tube, working at 50 kV and 0.8 mA (40 W), providing a beam spot of 120 µm [11]. For vorontsovite we have collected 1257 frames by 25 runs using an omega scan mode and an exposure time of 10 s. The data were collected up to 2θ max = 60 • .…”

Section: X-ray Crystallographymentioning

confidence: 99%

Vorontsovite, (Hg5Cu)Σ6TlAs4S12, and Ferrovorontsovite, (Fe5Cu)Σ6TlAs4S12: The Tl- and Tl-Fe-Analogues of Galkhaite from the Vorontsovskoe Gold Deposit, Northern Urals, Russia

et al. 2018

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Abstract:Two new mineral species, vorontsovite, ideally (Hg 5 Cu)TlAs 4 S 12 , and ferrovorontsovite, ideally (Fe 5 Cu)TlAs 4 S 12 , the Tl-and Tl-Fe-analogues of galkhaite, respectively, have been discovered at the Vorontsovskoe gold deposit, Northern Urals, Russia. They occur as anhedral grains up to 0.5 mm (vorontsovite) and 0.2 mm (ferrovorontsovite) embedded in a calcite-dolomite matrix. Σ4.00 S 12.00 . Both minerals are cubic, space group I-43m, with a = 10.2956(6) Å, V = 1091.3(1) Å 3 , Z = 2 (vorontsovite); and a = 10.2390(7) Å, V = 1073.43(22) Å 3 , Z = 2 (ferrovorontsovite). The crystal structures of both minerals were refined to R = 0.0376 (vorontsovite) and R = 0.0576 (ferrovorontsovite). Vorontsovite and ferrovorontsovite have been approved by the IMA-CNMNC under the numbers 2016-076 and 2017-007, respectively. The first one is named after the type locality, but also honors the mining engineer Vladimir Vasilyevich Vorontsov. The second is named for its chemical composition, as the Fe-analogue of the first. Both species are isostructural with galkhaite, being its Tl-and Tl-Fe analogues, respectively, and forming altogether the galkhaite group.

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A century of mineral structures: How well do we know them?

Cited by 29 publications

References 82 publications

High-quality structures at high pressure? Insights from inclusions in diamonds

High-quality structures at high pressure? Insights from inclusions in diamonds

Recent developments and the future of low‐T calorimetric investigations in the Earth sciences: Consequences for thermodynamic calculations and databases

Vorontsovite, (Hg5Cu)Σ6TlAs4S12, and Ferrovorontsovite, (Fe5Cu)Σ6TlAs4S12: The Tl- and Tl-Fe-Analogues of Galkhaite from the Vorontsovskoe Gold Deposit, Northern Urals, Russia

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