Crystal chemistry of dorrite from the Eifel volcanic region, Germany, and chemical variations in the khesinite-dorrite-rhönite-kuratite solid-solution system
Copyright policy )Crystal chemistry of dorrite from the Eifel volcanic region, Germany, and chemical variations in the khesinite-dorrite-rhönite-kuratite solid-solution system
Dorrite, khesinite and rhonite from metamorphosed calcic xenoliths of the Bellerberg paleovolcano (Eifel, Germany) were studied, including first determination of the crystal structure of natural dorrite (R = 0.0636). Dorrite is triclinic, P-1, unit-cell parameters are: a = 10.4316(7), b = 10.8236(9), c = 8.9488(7) A, α = 105.972(6), β = 96.003(9), γ = 124.67(10)° and V = 754.10(11) A3. Its crystal-chemical formula is (Z = 1): M8Ca2M9Ca2M1Fe3 + M2Fe3 + M3(Fe3+0.8Mg0.2)2M4(Fe3+0.8Mg0.2)2M5(Mg0.9Fe3+0.1)2M6(Mg0.5Fe3+0.5)2M7(Fe3+0.9Al0.1)2[T1(Al0.75Si0.20Fe3+0.05)2T2(Al0.77Si0.20Fe3+0.03)2T3(Al0.9Fe3+0.1)2T4Si2T5(Fe3+0.6Al0.4)2T6(Fe3+0.6Al0.4)2]O40. New and earlier published data show that khesinite, dorrite, rhonite and kuratite form a solid-solution system without significant gaps. The chemical variation and isomorphous substitutions in this system are discussed and the following simplified formulae are suggested: dorrite, Ca2(Fe3+,Mg)5Mg[(Al,Fe3+,Si)5SiO20], khesinite, Ca2(Fe3+,Mg)5Mg[(Fe3+,Al,Si)5SiO20], and rhonite, Ca2(Mg,Fe3+)5Ti[(Si,Al)6O20].
- Russian Academy of Sciences Russian Federation
- Institute of Problems of Chemical Physics Russian Federation
- Lomonosov Moscow State University Russian Federation
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