抄録
Nagashimalite, Ba4(V3+,Ti)4[(O,OH)2|Cl|Si8B2O27], is orthorhombic, space group Pmmn, unit cell parameters: a=13.937(3), b=12.122(3), c=7.116(2)Å, Z=2. The strongest lines in the X-ray powder pattern are: 3.854(25) (221), 3.319(15) (112), 3.173(15) (202), 3.030(60) (040, 411), 3. 020(100) (420), 2.791(20) (041), 2.592(28) (501, 241), 1.785(15) (641), 1.287(15) (771). It is greenish black in colour, lustre submetallic to vitreous. Streak green. No cleavage. VHN (load 100 g) 606–681 kg/mm2 (=6 (Mohs)). Specific gravity 4.08 (meas.), density 4.14 g/cm3(calc.). It is optically biaxial, positive, 2V=30°(obs.), r>v strong; refractive indices α=1.750(2), β=1.753(2), γ=1.780(5) ; optical orientation a=X, b=Z, c=Y; pleochroism strong, X=greenish yellow, Y=green, Z=greenish brown, absorption X<Y<Z. The mineral occurs as prismatic crystals and their aggregates in massive rhodonite ore from a bedded manganese ore deposit of the Mogurazawa mine, Gumma Prefecture, Japan.
