Clay Science
Online ISSN : 2186-3555
Print ISSN : 0009-8574
ISSN-L : 0009-8574
FLUOROKINOSHITALITE AND FLUOROTETRAFERRIPHLOGOPITE : NEW SPECIES OF FLUORO-MICA FROM BAYAN OBO, INNER MONGOLIA, CHINA
RITSURO MIYAWAKIHIDEHIKO SHIMAZAKIMASAKO SHIGEOKAKAZUMI YOKOYAMASATOSHI MATSUBARAHISAYOSHI YURIMOTOZHUMING YANGPEISHAN ZHANG
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2011 Volume 15 Issue 1 Pages 13-18

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Abstract

Two new species of F-mica, fluorokinoshitalite (BaMg_3Al_2Si_2O_<10>F_2) and fluorotetraferriphlogopite (KMg_3Fe^<3+>Si_3O_<10>F_2) occur in Bayan Obo, Inner Mongolia, China. They form subhedral to euhedral platy crystals in metamorphosed carbonate rocks. They are associated with phlogopite, yangzhumingite, and rare earth minerals such as bastnasite-(Ce), cordylite-(Ce), monazite-(Ce), fluorbritholite-(Ce) and huanghoite-(Ce). Fluorokinoshitalite is transparent and colorless with white streak and pearly luster. Cleavage is perfect on {001}. The calculated density is 3.235g cm^<-3>. Fluorotetraferriphlogopite is brown in color with white to pale brown streak. It is transparent showing pearly luster and perfect cleavage on {001}. The hardness is 3-4 on the Mohs scale. The calculated density is 2.966g cm^<-3>. This mineral is optically biaxial (-) with n=1.576 (min.)-1.582 (max.). It shows reverse pleochroism (Z'=colorless, X'=light brown). Electron microprobe analyses with SIMS for Li gave empirical formulae (based on 12 anions); (Ba_<0.56>Na_<0.25>K_<0.06>)(Mg_<2.76>Fe^<2+>_<0.14>Ti_<0.01>) (Si_<2.73>Al_<1.15>Fe^<3+>_<0.12>)O_<10>[F_<1.72>(OH)_<0.28>] and (K_<0.94>Na_<0.02>Ba_<0.01>)(Mg_<2.62>Li_<0.15>Fe^<+2>_<0.14>_Mn_<0.01>)(Si_<3.33>Fe^<3+>_<0.66>Al_<0.01>)O_<10>[F_<1.65>(OH)_<0.35>] for fluorokinoshitalite and fluorotetraferriphlogopite, respectively. The lattice parameters were refined in the monoclinic system (C2/m) with the XRD data obtained with an IP-Gandolfi camera as; a=5.3161 (11), b=9.2082(15), c=10.044(2) Å, β=100.158(18)°, V=483.97(17) Å^3 (fluorokinoshitalite) and a=5.325(3), b=9.217(5), c=10.192(7) Å, β=100.03(5)°, V=492.6(5) Å^3 (fluorotetraferriphlogopite).

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© 2011 The Clay Science Society of Japan
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