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Magnesio-arfvedsonite from Jade Mine Tract, Myanmar: mineral description and crystal chemistry

Published online by Cambridge University Press:  02 January 2018

Roberta Oberti*
Affiliation:
CNR-Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1, I-27100 Pavia, Italy
Massimo Boiocchi
Affiliation:
Centro Grandi Strumenti, Università di Pavia, via Bassi 21, I-27100 Pavia, Italy
Frank C. Hawthorne
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
Neil A. Ball
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
George E. Harlow
Affiliation:
Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street New York, NY 10024-5192, USA
*

Abstract

Magnesio-arfvedsonite, the CFe3+-dominant analogue of eckermannite, has been found in a sample of “szechenyite” in the mineral collection of the American Museum of Natural History (AMNH H35024). It comes from the northern part of the Jade Mine Tract near Hpakan, Kachin State, Myanmar. Associated minerals are kosmochlor–jadeite solid-solution pyroxene and clinochlore. The ideal formula of magnesio-arfvedsonite is ANaBNa2C(Mg4Fe3+)TSi8O22W(OH)2, and the empirical formula derived from electron microprobe analysis and single-crystal structure refinement for the sample of this work is A(Na0.96K0.04)Σ=1.00B(Na1.57Ca0.40Fe0.022+Mn0.01)Σ=2.00C(Mg4.26Fe0.192+Fe0.413+Al0.11Ti0.034+)Σ=5.00T(Si7.99Al0.01)Σ=8.00O22W[F0.02(OH)1.98]Σ=2.00. The unit-cell dimensions are a = 9.867(1), b = 17.928(2), c = 5.284(1) Å, β = 103.80(2)°, V = 907.7 (2) Å3, Z = 2. Magnesio-arfvedsonite is biaxial (–), with α = 1.624, β = 1.636, γ = 1.637, all ± 0.002 and 2Vobs = 36(1)°, 2Vcalc = 32°. The ten strongest reflections in the X-ray powder pattern [d values (in Å), I, (hkl)] are: 2.708, 100, (151); 3.399, 68, (131); 3.144, 63, (310); 2.526, 60, (202); 8.451, 46, (110); 3.273, 39, (240); 2.167, 37, (261); 2.582, 34, (061); 2.970, 34, (221); 2.326, 33, [(251) (421)].

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2015

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