Crystal structures have been refined from singlecrystal X-ray data for nine synthetic clinopyroxenes in the system NalnSi206-NaScSi206, crystallized at 1770 K and 6 GPa pressure. The structures are isomorphous with other sodium pyroxenes. The space group is C2/c, Z=4. In and Sc occupy a distorted octahedral (M1) site. The M1--M1 dis-0108-7681/90/060742-06503.00 tances and the M1--O1--M1 angles correlate with the mean M1--O1 distances in such a way as to follow two different trends, suggesting that there are two different electronic states for the octahedral In 3 ÷ ions. The Si--O distances constitute two populations which can be related to the mean electronegativity of the octahedral (M1) ions. From the Si--O distances, the electronegativites of the two In 3÷ ions are 1.2 and 1.7 on Pauling's scale.(
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