VIVIANITE FROM HIMESHIMA, OOITA PREFECTURE, JAPAN

Studies on Vivianite from Japan, Rept. 1

抄録

Vivianite nodules 1-8cm. in diameter, some of them taking the shape of tree-trunk or mammal bone, have been found in gravels and mudstone bed at the beach Subana in the Island of Himeshima, Ooita Prefecture, Japan. They are composed of radial aggregates of foliated vivianite crystals. The specimens collected from the gravels are covered with brown film of limonite. The observation on the fresh vivianite from Himeshima follows; colour: yellowish or deep blue, streak: blue, hardness: 1.5-2, sp. gr.: 2.66 at 17°C., cleavage: (010) easy, luster: vitreous, indices of refraction: α=1.587, β=1.607 and γ=1.631, 2V large, pleochroism: X blue, Y colourless or yellowish and Z yellowish, optical orientations: X//b, Z∧c about 27°. Small but good crystals of vivianite are found on the wall of druses. They have short prismatic habit with monoclinic symmetry. Forms: b (010), m (110), w ( ?? 01), T (103), d (801), x (221) and V (441). The result of chemical analysis of a nodular specimen follows, P₂O₅ 24.43, Al₂O₃ 2.49, Fe₂O₃ 6.84, FeO 30.04, MnO 0.24, MgO 0.28, CaO 0.06, Na₂O tr., K₂O tr., TiO₂ tr., SiO₂ non., SO₃ non., insol. 10.36, H₂O (+) 13.05, H₂O (-) 12.65, total 100.44%, and that of a specimen in tree trunk shape follows, P₂O₅ 26.84, Al₂O₃ 0.59, Fe₂O₃ 14.00, FeO 29.30, MnO tr., MgO 0.10, CaO 0.12, SiO₂ 0.42, insol. 0.06, H₂O (+) 16.11, H₂O (-) 12.35, total 99.89%. In the nodular sample, some clay inclusions are observed under the microscope. The main features of X-ray powder diagram of the tree-trunk-shaped specimen agrees with that of the well crystallized vivianite from the Ashio mine, Tochigi Prefecture, Japan.