Abstract

Chemical and crystallographic properties of clinopyroxene exsolution in wollastonite are described from metamorphosed calc-silicate granulite, Namaqualand, South Africa. The wollastonite is Ca1.96Fe0.01Al0.01Si2.01O6 belonging to space group P21/a (2M polytype) and the clinopyroxene is Ca0.99Mg0.75–0.80Fe0.17–0.21Na0.02Al0.03Si1.99–2.00O6 belonging to C2/c. An electron backscattered diffraction investigation suggests that the clinopyroxene lamellae elongated along [1̅1̅1] lie on (120) and (100) of the wollastonite-2M, and [11̅0] of both lamellae are parallel to [001] of the wollastonite-2M. The formation of the exsolution probably results from the relatively high peak metamorphic temperature (800–860°C) of the Namaqualand granulite and its slow cooling rate.

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