• journal_title：American Mineralogist
• Contributor：Yusuke Seto ; Shugo Ohi ; Norimasa Shimobayashi ; Masao Kitamura ; Akira Miyake ; Yoshikuni Hiroi ; Geoffrey H. Grantham
• Publisher：Mineralogical Society of America
• Date：2006-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2006.2063
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：91
• issue：2-3
• firstpage：446
• section：Articles

Chemical and crystallographic properties of clinopyroxene exsolution in wollastonite are described from metamorphosed calc-silicate granulite, Namaqualand, South Africa. The wollastonite is Ca<sub>1.96sub>Fe<sub>0.01sub>Al<sub>0.01sub>Si<sub>2.01sub>O<sub>6sub> belonging to space group P2<sub>1sub>/a (2M polytype) and the clinopyroxene is Ca<sub>0.99sub>Mg<sub>0.75–0.80sub>Fe<sub>0.17–0.21sub>Na<sub>0.02sub>Al<sub>0.03sub>Si<sub>1.99–2.00sub>O<sub>6sub> 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.