Astrophyllite from the Namjabarwa Area, Eastern Tibet
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    Abstract:

    The Namjabarwa area the core of the eastern Himalayan syntaxis, is the least-known part of the Himalayas. Recent research has revealed that this area consists of three tectonic units, viz. the Gangdise unit , the Yarlung Zangbo unit, and the Himalayan unit, separated from each other by faults. The Himalayan unit consists of amphibolite facies rocks in the south and granulite facies rocks in the north, with the latter rocks displaced south-ward over the former along the Namula thrust system. As an accessory minral in a carbonate vein that intruded the granulite facies rocks, astrophyllite is associated with dolomite , calcite, olivine, spinel,phlogopite, pargasite, apatite, garnet (Gr24.5Alm49.6 PYr18.6And6.7),geikielite and three unknown minerals. One of these unknown minerals is composed of B, C,Mg, Ti,Fe and Al,being probably a new mineral.The unit cell parameters of astrophyllite are a0)=5.356 (1)Å,b0=11.607 (4)Å,c0=11.851 (6)Å ,a=64.57º(3),β=76.98º(4), γ=85.45º(3).Electron microprobe analysis (average of three samples)gave SiO2 35.22, TiO2 11 .47,Al2O31.18,Fe0 28.90,Mn0 5.15,MgO 1.51,Ca0 1.75,K20 5.90,and Na20 2.46, totally 93 .54%,corresponding to the formula of ( K,Na)3 (Fe, Mn, Mg, Ca)7 Ti2Si8O24(O,OH)7,which indicates that the astrophyllite is of a new mode of occurrence.

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刘 焰,马喆生,韩秀伶,周湖云,张培善,钟大赉,1997,西藏南迦巴瓦峰地区发现的星叶石[J].岩石矿物学杂志,16(4):337~340.,1997,Astrophyllite from the Namjabarwa Area, Eastern Tibet[J]. Acta Petrologica et Mineralogica,16(4):337~340.

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