Abstract
Coexisting zoisite and clinozoisite assemblages in biotite schists from the western Hohe Tauern, Austria, have been investigated with the electron microprobe, polarization optics, and X-ray diffractometer. Zoisite and clinozoisite show slight compositional zoning, ranging from the core to the rim from about 1.8 to 1.0 wt. % Fe in zoisite, and 4.0 to 3.0 wt. % Fe in clinozoisite. The results suggest a gap of composition between coexisting zoisite and clinozoisite under greenschist-amphibolite transition facies conditions.
The optical orientation and 2V of zoisite vary considerably within single grains. Lamellar structures have been detected which may be produced by unmixing of zoisite. The Fe-poor lamellae have 2V z=20–50°, a dispersion r>v, and relatively low refringence, the Fe-rich lamellae have 2V z =90–100°, r≪v, and higher refringence. The optic axial planes of both lamellae systems deviate from the (100) cleavage by up to 15°, and suggest a deviation from orthorombic symmetry. The lattice constants of coexisting zoisite and clinozoisite are given.
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Ackermand, D., Raase, P. Coexisting zoisite and clinozoisite in biotite schists from the Hohe Tauern, Austria. Contr. Mineral. and Petrol. 42, 333–341 (1973). https://doi.org/10.1007/BF00372611
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DOI: https://doi.org/10.1007/BF00372611