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Sadanagaite and magnesio-sadanagaite, new silica-poor members of calcic amphibole from Japan

1984; Mineralogical Society of America; Volume: 69; Linguagem: Inglês

1945-3027

Hidehiko Shimazaki, Michiaki Bunno, Tohru Ozawa,

Zeolite Catalysis and Synthesis

Sadanagaite, (K,Na)Ca2(Fe2+ ,Mg,AI,Fe3+ ,Ti)5[(Si,A1)8022(OH)2J where Fe2+ ~ Mg, Al ~ Fe3+ and Si < 5.5, and its Mg-rich analogue, magnesio-sadanagaite Fe2+ < Mg, are extremely Si02-poor new amphiboles, which require the compositional extension of the edenite-pargasite series, and amending of the classification and nomenclature of amphiboles (Leake, 1978). These are monoclinic, C2, Cm or C2/m; a = 9.922(10), b = 18.03(2), c = 5.352(9)A, f3 = 105.30(10)°, Z = 2 for sadanagaite with Si = 5.0, and a = 9.964(2), b = 18.008(3), c = 5.354(2)A, f3 = 105.55(2)°, Z = 2 for magnesio-sadanagaite with Si = 5.0. The strongest lines in the X-ray powder pattern for magnesio-sadanagaite are: 8.48(80)(IIQ), 3.39(40)(131), 3.28(100)(240), 3.15(70)(310), 2.951(50)(221), 2.823(30)(330), 2.766(45)(331), 2.707(60)(151), 2.594(35)(061), 2.162(55)(261), 1.654(30)(461), these being similar to those of X-ray powder patterns of Si02-poor calcic amphiboles, especially kaersutite. Both species have very similar physical properties, and are dark brown to black with a vitreous luster. Streak very light brown. Cleavage {110}, perfect. H (Mohs) = 6. Density (calc.) 3.30 g/cm3 for sadanagaite and 3.27 g/cm3 for magnesio-sadanagaite. Optically biaxial positive with 2V = 80-90° (meas.), 86° (calc.) for sadanagaite, and with 2V close to 90° (meas.), 88° (calc.) for magnesio-sadanagaite. Refractive indices: a = 1.673(2), f3 = 1.684(2), 'Y = 1.697(2); c:Z = 28° (sadanagaite), and a = 1.674(2), f3 = 1.686(2), 'Y = 1.699(2); c:Z = 26° (magnesio-sadanagaite). Pleochroism strong with X' = pale brown to Z' = greenish brown (sadanagaite) and with X' = colorless to Z' = brownish yellow (magnesio-sadanagaite) . The minerals are found in two separate localities, Yuge and Myojin Islands, Japan, where they occur in AI-, Tiand Fe-rich skarns in recrystallized limestone beds, forming bands with vesuvianite, spinel-hercynite, sphene, ilmenite and apatite in the former locality, and forming small lenses with titaniferous fassaite, vesuvianite, spinel-hercynite, sphene, ilmenite, magnetite, apatite and perovskite in the latter. Among them the peculiar composition of titaniferous fassaite is discussed with special reference to its extremely Si02-poor, Ah03and Ti02-rich composition. The names are for Professor Ryoichi Sadanaga, Mineralogical Institute, University of Tokyo, in recognition of his outstanding contributions to the fields of mineralogy and crystallography. 1 Present address: Geological Department, Geological Survey of Japan, Higashi 1-1-3, Yatabe, Ibaraki 305, Japan. 0003-004X/84/0506-0465$02.00 465 466 SHIMAZAKI ET AL.: SADANAGAITE AND MAGNESIO-SADANAGAITE