Pink Zoisite from the Aar Massif, Switzerland

J. Abrecht*
Mineralogisch-petrographisches Institut der Universität, 3012 Bern, Switzerland
*Present address: Department of Geological Sciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, VA 24061, USA.

Abstract: Veins in the Central Aar granite consisting of zoisite, plagioclase, albite, alkali feldspar, muscovite, tremolite, quartz, and calcite are described. The zoisite is a thulite with up to 0.20 wt% MnO. It is argued that the zoisite is derived from granite plagioclases and has recrystallized in veins during alpine greenschist metamorphism. By later increasing XCO2 or decreasing temperature zoisite decomposed to calcite, plagioclase, and muscovite.

Thulites from different localities were investigated by X-ray and by electron microprobe analysis. Both orthorhombic and monoclinic members of the epidote group having low MnO contents have been described as thulites. It is suggested that low MnO values in the range 0.05 to 0.9 wt% cause the pink colour of thulites, regardless of symmetry.

Mineralogical Magazine; March 1981 v. 44; no. 333; p. 45-49; DOI: 10.1180/minmag.1981.44.333.05
© 1981, The Mineralogical Society
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