Mg2+ – Fe2+ order in an orthopyroxene, Mg0.93Fe1.07Si2O6
Abstract
The structure of an intermediate orthopyroxene, Mg0.93Fe1.07Si2O6 with cell dimensions a = 18.310, b = 8.927, c = 5.226 Å; space group: Pbca, derived from a high-grade metamorphic rock, has been refined by the method of least squares using three-dimensional intensity data. The R factor for 1028 reflections is 0.118. The average standard deviation of M–O, as well as Si–O bond lengths is 0.014 Å.
Mg2+ and Fe2+ are virtually completely ordered, the ordering scheme being the same as that proposed by Ghose (1962). The M1 site, corresponding to the Mg site in diopside, CaMgSi2O6, contains 85% Mg2+ and 15% Fe2+ and the M2 site, corresponding to the Ca site in diopside, contains 90% Fe2+ and 10% Mg2+. M2–O2 (2.07 Å) and M2–O5 (2.04 Å) bonds are significantly shorter than the sum of Pauling's crystal radii (2.16 Å) and have considerable covalent character.
The two crystallographically distinct silicate chains have slightly different configurations, caused by slight rotations of Si1 and Si2 tetrahedra, with Si1–O1 and Si2–O4 as axes. The average Si–O bond length is 1.63 Å. The non-bridging Si–O bonds (1.60 Å) are significantly shorter than the bridging Si–O bonds (1.66 Å).
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Artikel in diesem Heft
- Die Kristallstruktur von bis-Cyclooctadien-(1,5)-Nickel(0)
- Corrections for x-ray absorption by a crystal of arbitrary shape1
- Kristall- und Molekülstruktur von bis-Methallylnickel Ni[(CH2)2C · CH3]2
- A preliminary orienting procedure for single crystals, using the Weissenberg camera
- Mg2+ – Fe2+ order in an orthopyroxene, Mg0.93Fe1.07Si2O6
- On the x-ray determination of the iron-magnesium ratio in biotites
- Phases and twinning in C2Al3B48 (beta AlB12)
- Packing of B12 groups in boron and boride structures
- A crystallographic study of ammonium and rubidium imidodisulphates
- Interstitial derivatives of β boron
- Die Intensität der an gebogenen Glimmerspaltflächen in höheren Ordnungen reflektierten Röntgenstrahlung
- Morphology and space group of hexaantipyrine perchlorate complexes of Mg++, Ca++ and Zn++, and pentaantipyrine perchlorate of Cu++
- Kristallographische Daten von Quecksilber(I)-acetat
- Preliminary x-ray crystallographic data for 3,7-dideoxy-7-iodo-heptulosonate methyl ester
