Comparative Compressibilities of Majorite- Type Garnets
نویسنده
چکیده
Relative compressibilities of five silicate garnets were determined by single-crystal x-ray diffraction on crystals grouped in the same high-pressure mount. The specimens include a natural pyrope [(Mgz.84Feo.IOCao,o6) AI2Si30d, and four synthetic specimens with octahedrally-coordinated silicon: majorite [Mg3(MgSi)Si30 d, calcium-bearing majorite [(Cao.49Mg2.sl)(MgSi)Si30d, sodium majorite [(NaI.88Mgo.d(Mgo.o6SiI.94)Si3012J, and an intermediate composition [(Nao.37Mg2.48)(Mgo.I3All.o7 Sio.8o)Si30I2]. Small differences in the compressibilities of these crystals are revealed because they are subjected simultaneously to the same pressure. Bulk-moduli of the garnets range from 164.8:t 2.3 GPa for calcium majorite to 191.5 :t2.5 GPa for sodium majorite, assuming K' =4. Two factors, molar volume and octahedral cation valence, appear to control garnet compression.
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تاریخ انتشار 2005