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Sadanagaite and subsilicic ferroan pargasite from thermally metamorphosed rocks in the Nōgō-Hakusan area, central Japan

Published online by Cambridge University Press:  05 July 2018

Takayuki Sawaki
Takayuki Sawaki*
Affiliation:
Department of Earth Sciences, Faculty of Science, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan
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Abstract

High-alumina subsilicic calcic amphiboles, including sadanagaite and subsilicic ferroan pargasite, are found in rock samples from the contact aureole in the Nōgō-Hakusan area, central Japan. They occur in the reaction zones between dark fragments and the surrounding crystalline limestone of the pyroxene hornfels facies zone. The dark fragments which underwent K-metasomatism are originally basaltic rocks. The sadanagaite and subsilicic ferroan pargasite have high Al2O3 (16–19 wt. %) and K2O (3.6–4.3 wt. %) contents. The Si value ranges from 5.38 to 5.64 and the total Al ranges from 3.10 to 3.43 when cation ratios are calculated on the basis of O = 23. The calculated unit cell parameters of sadanagaite are a 10.00 (1), b 18.06 (2), c 5.355 (4) Å, β105.52(7)°, V 932(1) Å3. The A-sites of the amphiboles is occupied almost entirely by K and Na; the amphiboles are saturated with the edenite component. The amphiboles show a larger extent of tschermakite-type substitution [(Mg,Fe)Si⇌AlAl] than does ordinary pargasite. Sadanagaite is probably stable at the temperature above the upper amphibolite facies.

Keywords

sadanagaitereaction zonepyroxene hornfels faciesNōgō-Hakusan areaJapan
Type
Mineralogy
Information
Mineralogical Magazine , Volume 53 , Issue 369 , March 1989 , pp. 99 - 106
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1989

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