抄録
Nagashimalite, Ba4(V3+3.44Ti0.56)B2Si8O28Cl[(OH)0.44O0.56], a new mineral from the Mogurazawa mine, Gumma Prefecture, is orthorhombic, space group Pmmn, with unit cell parameters a=13.937(3), b=12.122(3), c=7.116(2)Å and Z=2.
The crystal structure is similar to that of taramellite after Mazzi and Rossi (1965), except for boron and chlorine. It basically consists of a novel borosilicate group [Si8B2O27] which is built up of a pair of Si4O12 groups linked together, sharing corners, by a B2O7 group. These borosilicate groups are in the structure joined together by sharing of octahedra, parallel to b, formed by oxygen atoms about vanadium atoms. The crystallochemical formula is thus given as Ba4(V3+,Ti)4[(O, OH)2|Cl|Si8B2O27]. Mean interatomic distances are: V–O=2. 012(5), Si(1)–O=1.631(4), Si(2)–O=1.617(4), and B–O=1.479(5)Å. The Ba atoms are thirteen and eleven-coordinated with mean distances of Ba(1)[13]–(O, OH)=3.094(6), Ba(2)[11]–(O, Cl)=3.121(8), and Ba(3)[11]–(O, Cl)=2.925(8)Å.
It appears that the reported taramellite structure would in fact contains boron atoms and belongs to the same borosilicate groups as nagashimalite.
