Residual electron density at theM2 site inC2/c clinopyroxenes: Relationships with bulk chemistry and sub-solidus evolution

Rossi, Giuseppe; Oberti, Roberta; Negro, A. Dal; Molin, Gianmario; Mellini, Marcello

doi:10.1007/bf00308286

Cited by 62 publications

(31 citation statements)

References 21 publications

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“…For several representative clinopyroxenes a significant residual electron density, centred close to the M2 sites, has been inferred from X-ray structure refinement. According to Rossi et al (1987) this phenomenon is caused by an offcentre displacement of the relatively small sized cations within the M2 polyhedron (like Ni 2+ in our case which substitutes larger Ca 2+ (r oct is 0.69 Å and 1.00 Å, respectively (Shannon 1976)). shorter, whereas four longer bonds become longer.…”

Section: Resultsmentioning

confidence: 75%

Optical spectroscopic study of synthetic NaScSi2O6–CaNiSi2O6 pyroxenes at normal and high pressures

Taran

Ohashi²,

Koch‐Müller

2007

Phys Chem Minerals

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Section: Resultsmentioning

confidence: 75%

Optical spectroscopic study of synthetic NaScSi2O6–CaNiSi2O6 pyroxenes at normal and high pressures

Taran

Ohashi²,

Koch‐Müller

2007

Phys Chem Minerals

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“…close to the position and coordination of Fe M2 of clinoferrosilite. Although more regular, the new M2' position is still higher distorted than the M1 site (Rossi et al, 1987). Following Dyar et al (1989) and Li et al (2005), we assigned the MS doublet with the highest quadrupole splitting to Fe 2+ at the more regular M1 site, the doublet with lower quadrupole splitting to Fe 2+ at the distorted M2 site and the MS doublet with low quadrupole splitting is assigned to Fe 3+ at M1 (Table 4).…”

Section: Characterization Of the Samples Prior To Heatingmentioning

confidence: 82%

“…As well known from several studies Fe 2+ prefers the more distorted M2 site and Fe 3+ the octahedral M1 site (e. g. Dyar et al, 1989;Oberti and Caporuscio, 1991;Li et al, 2005). According to Rossi et al (1987) the M2 site may also be occupied by small amounts of Mg. In case of (Fe 2+ and Mg)-M2 site occupation the M2 site splits into a M2' position approximately 0.4 Å along the b-axis and toward the oxygen atoms O1 and O2, i.e.…”

Section: Characterization Of the Samples Prior To Heatingmentioning

confidence: 84%

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Dehydration experiments on natural omphacites: qualitative and quantitative characterization by various spectroscopic methods

et al. 2007

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Originally published as:Koch-Müller, M., Abs-Wurmbach, I., Rhede, D., Kahlenberg, V., Matsyuk, S. (2007) AbstractA series of natural omphacites from a wide range of P, T occurrences were investigated by electron microprobe (EMP), infrared (IR)-, Mössbauer (MS)-and optical spectroscopy in the UV/VIS spectral range (UV/VIS), secondary ion mass spectrometry (SIMS) and single crystal structure refinement by X-ray diffraction (XRD) to study the influence of hydrogen loss on valence state and site occupancies of iron. In accordance with literature data we found Fe 2+ at M1 as well as at M2, and in a first approach assigned Fe 3+ to M1, as indicated by MS and XRD results. Hydrogen content of three of our omphacite samples were measured by SIMS. In combination with infrared spectroscopy we determined an absorption

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“…The semiempirical absorption correction of Blessing (1995), based on the determination of transmission factors for equivalent reflections, was applied using the program SADABS (Sheldrick 1996) site. The first feature had been already observed by Rossi et al (1987), and was added to the model as a split position (M21), with the atomic coordinates of the residual (ca. x = 0, y = 0.26, z = ½).…”

Section: X-ray Single-crystal Diffraction and Structure Refinementmentioning

confidence: 99%

Thermal history of nakhlites: A comparison between MIL 03346 and its terrestrial analogue Theo’s flow

Domeneghetti¹,

Fioretti²,

Cámara³

et al. 2013

Geochimica et Cosmochimica Acta

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High resolution single-crystal X-ray diffraction (HR-SCXRD) Analysis (EMPA) and the X-ray structural data allowed us to obtain the accurate cation site distribution and the Fe 2+ -Mg degree of order. This leads to a closure temperature (Tc) of 500 with a standard deviation of ± 100°C that would correspond to a slow cooling rate, which is in disagreement with petrologic evidence that indicates that this sample originates from a fast cooled (~ 3-6°C/h) lava flow .In order to clarify this discrepancy we undertook (i) a SC-XRD study of an augite (~ En49Fs9 Wo42) from a pyroxenite (TS7) of Theo's flow, a 120-m-thick lava flow regarded as a terrestrial analogue of MIL 03346; (ii) an annealing experiment at 600°C on a crystal from exactly the same fragment of MIL 03346. SC-XRD data from TS7 augite yields a Tc= 600(20)°C, consistent with the cooling rate expected at 85m below the surface. This Tc is higher, although similar within error, to the Tc=500(100)°C obtained for MIL03346; thus suggesting relatively slower cooling for MIL 03346 with respect to TS7. The annealing experiment on the MIL 03346 crystal clearly showed that the degree of order remained unchanged, further confirming that the actual Tc is close to 600°C.This result appears inconsistent with the shallow depth of origin (~ <2m) assumed for MIL 03346, further supporting the discrepancy between MIL 03346 textural and petrologic evidence of fast cooling and the abovementioned Tc results obtained for augite. Therefore, a tentative scenario is that, soon after eruption and initial quench and while still at relatively high-T (~ 600°C), MIL 03346 was blanketed with subsequent lava flows that slowed down the cooling rate and allowed the augite Fe 2+ -Mg exchange reaction to proceed.

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Residual electron density at theM2 site inC2/c clinopyroxenes: Relationships with bulk chemistry and sub-solidus evolution

Cited by 62 publications

References 21 publications

Optical spectroscopic study of synthetic NaScSi2O6–CaNiSi2O6 pyroxenes at normal and high pressures

Optical spectroscopic study of synthetic NaScSi2O6–CaNiSi2O6 pyroxenes at normal and high pressures

Dehydration experiments on natural omphacites: qualitative and quantitative characterization by various spectroscopic methods

Thermal history of nakhlites: A comparison between MIL 03346 and its terrestrial analogue Theo’s flow

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