1961The Journal of the Japanese Association of Mineralogists Petrologists and Economic GeologistsOpen access

On the augite phenocryst in alkali basalts from the Abu district

Yoshio Oji

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Abstract

Two phenocrystic augites in trachybasalts from the Abu district, Yamaguchi prefecture are microscopically and chemically investigated. As a result, it is found that augite from Horikoshi is diopsidic augite expressed by chemical formula (Ca0.87Na0.02)0.89(Fe''0.11Fe'''0.06Mg0.90Ti0.01Al0.02)1.10(Si1.92Al0.08)2.00O6.00 and that augite from Kunigatoge is titanaugite by chemical formula (Ca0.85Na0.03)0.88(Fe''0.12Fe'''O.08Mg0.77Ti0.03Al0.08)1.08(Si1.83Al0.17)2.00O6.00 In the evolution of the clinopyroxene in trachybasalt from this district, the composition of the former augite represents the earliest stage, while the later represents the latest one, so the crystallization trend of clinopyroxene of this district can be assumed parallel to the Di-Hd line within the field of augite-salite as stated by Wilkinson.

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Two phenocrystic augites in trachybasalts from the Abu district, Yamaguchi prefecture are microscopically and chemically investigated. As a result, it is found that augite from Horikoshi is diopsidic augite expressed by chemical formula (Ca0.87Na0.02)0.89(Fe''0.11Fe'''0.06Mg0.90Ti0.01Al0.02)1.10(Si1.92Al0.08)2.00O6.00 and that augite from Kunigatoge is titanaugite by chemical formula (Ca0.85Na0.03)0.88(Fe''0.12Fe'''O.08Mg0.77Ti0.03Al0.08)1.08(Si1.83Al0.17)2.00O6.00 In the evolution of the clinopyroxene in trachybasalt from this district, the composition of the former augite represents the earliest stage, while the later represents the latest one, so the crystallization trend of clinopyroxene of this district can be assumed parallel to the Di-Hd line within the field of augite-salite as stated by Wilkinson.

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Available abstract

Two phenocrystic augites in trachybasalts from the Abu district, Yamaguchi prefecture are microscopically and chemically investigated. As a result, it is found that augite from Horikoshi is diopsidic augite expressed by chemical formula (Ca0.87Na0.02)0.89(Fe''0.11Fe'''0.06Mg0.90Ti0.01Al0.02)1.10(Si1.92Al0.08)2.00O6.00 and that augite from Kunigatoge is titanaugite by chemical formula (Ca0.85Na0.03)0.88(Fe''0.12Fe'''O.08Mg0.77Ti0.03Al0.08)1.08(Si1.83Al0.17)2.00O6.00 In the evolution of the clinopyroxene in trachybasalt from this district, the composition of the former augite represents the earliest stage, while the later represents the latest one, so the crystallization trend of clinopyroxene of this district can be assumed parallel to the Di-Hd line within the field of augite-salite as stated by Wilkinson.

Key concepts: Augite, Phenocryst, Basalt, Alkali metal, Geochemistry, Chemistry, Geology, Volcano

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