岩手県田野畑鉱山産新鉱物神津閃石について

抄録

New mineral kôzulite belongs to the alkali amphibole group in which manganese (II) is the predominant cation of the Y-position. The mineral occurs as banded aggregate of short prismatic crystala with the faces of b, m and r up to 3.5×2.0×1.5mm in size, in the bedded magnanese deposit of Tanohata Mine, Iwate Prefecture, Japan, in the highly metamorphosed Jurassic chert-hornfels by the intrusion of granodiorite. Associated minerals are braunite, rhodonite, manganiferou alkali pyroxene, manganiferou alkali amphibole and quartz.
Color reddish black to black, streak light purplish brown, luter vitreous, H. 5, G. measured 3.30, calculated 3.36. Cleavage (110) perfect. Optically biaxial negative, ns α=1.685, β=1.717(mean), γ=1.720, 2Vα=34-36°, cΛX=25°. Strongly pleochroic with X yellow-brown, Y reddish brown, Z dark brown, absorption Z⟩Y⟩X, dispersion very weak, probably r⟩v.
Chemical analysis gave SiO₂ 51.38, TiO₂ none, Al₂O₃ 1.69, Fe₂O₃ 2.85, FeO none, MnO 27.96, ZnO 0.03, MgO 2.71, CaO 1.12, BaO none, Na₂O 8.41, K₂O 1.36, H₂O (-) 0.06, F 0.08, sum 99.75-O (=F₂) 0.03=99.72%, corresponding to (Na_2.54 K_0.27 Ca_0.19)_3.00 [(Mn_3.69 Mg_0.63)_4.32 (Fe⁺³_0.33Al_0.31)_0.64]_4.96Si_8.00O_21.78[(OH)_2.18F_0.04]_2.22, as O+OH+F=24.
The x-ray powder data showed the mineral to be monoclinic with a₀=9.91, b₀=18.13, c₀=5.28Å, β=104.5° and precession photographs of the same specimens by N. Morimoto, Osaka University, showed it to be monoclinic, space group C2/m, a=9.91±0.02, b=18.11±0.04, c=5.30±0.02Å, β=104.6°±0.1°, Z=2. The strongest x-ray lines are 8.51 (100) (110), (4.52) (10) (040), 3.40 (10) (131), 3.29 (17) (240), 3.15 (67) (310), 2.96 (6) (221), 2.827 (31) (330), 2.748 (8) (331), 2.722 (10) (151), 2.602 (6) (061), 2.545 (6) (202), 2.349 (7) (351), 2.174 (9) (261), 1.908 (7) (510), 1.447 (7) (661). The high-temperature x-ray study and DTA indicate that the mineral breaks down to braunit plus glas at about 950°C.
The name is for late Dr. Shukusuke Kôzu (1880-1955), formerly Professor in Tohoku University, Japan who made many contributions to the study of rock forming minerals. Type material is preserved at Tohoku University.
The mineral and name were approved before publication by the Commission on New Minerals and Mineral Names, IMA.