Synthesis, lattice constants and OH-valence vibrations of an orthorhombic amphibole with excess OH in the system Li2O-MgO-SiO2-H2O

✍ Scribed by W. V. Maresch; K. Langer

• Publisher: Springer
• Year: 1976
• Tongue: English
• Weight: 659 KB
• Volume: 56
• Category: Article
• ISSN: 0010-7999
• DOI: 10.1007/bf00375419

✦ Synopsis

Orthorhombic amphiboles with excess OH, which can be schematically deduced from anthophyllite by the combined substitutions Mg2+4-0 2-~ Li + +OH-and Mg 2+ -~ 2 Li +, were synthesized at 750-875 ~ C/1 kbar PH2o in the system Li20-MgO-SiO2-HzO.

Their phase relations are presented for 800 ~ C/1 kbar PH2o. An amphibole with the analytical composition 2.70 wt% Li20 , 31.1 wt % MgO, 63.0 wt % SiO2, and 3.29 wt% H20 has lattice constants a o 18 9 (11), b o 17 9 (10), c o 5.262 (3) A, V o 1,757.2 (1.5) A 3 (referred to Space Group Pnma). The OH-valence vibrational spectrum of this amphibole showed Vou bands at 3,667, 3,708, and 3,725 (shoulder) cm -t, which are ascribed to OH in the configurations (MgMgMg)-OH, (MgMgMg)-OH-Li (Li in the A-site) of the pseudotrigonal (M1 M 1 M3)-OH arrangement in the amphibole structure, and to Si-OH, respectively 9 No explanation can at present be offered for an additional shoulder at 3,695 cm -1. The proposed structural formula is (Li0.27 [--]0.73)(Li1.11 Mgo.89 ) 9 (Mg5)(Sis. m O21.20(OH)0.80)(OH)2.00.