A joaquinite-like mineral from Ohmi, Niigata Prefecture, Central Japan

抄録

A joaquinite-like new mineral was found from Ohmi, Niigata Prefecture, Central Japan in 1971. Chemical analysis gave, in weight %, SiO₂ 35.12, Nb₂O₅ 1.42, TiO₂ 12.48, A1₂O₃ 0.27, REE₂O₃ 1.12, FeO 4.75, CaO trace, SrO 5.85, BaO 31.31, ZrO 0.19, MgO 0.03, Na₂O 2.74, K₂O 0.94, MnO trace, H₂O+2.59, H₂O-0.47, total 99.36, corresponding to
(Na_0.97K_0.03)_1.00(Ba_2.76Sr_0.76Na_0.23^*RE_0.12Fe⁺³_0.12Mg_0.01)_4.00(Fe³⁺_0.79^**Nb_0.13Ti_0.l3Zr_0.02) _1.07Ti_2.00(Si_7.94Al_0.06)_8.00O_24.66(OH)_3.02
^*RE wt.=100 ^**Ta₂O₅=0
The precession photographs show this mineral to be orthorhombic with a 9.777±0.005Å, b 10.517±0.006 Å, c 22.392±0.12Å, and possible space guoup Pcam or Pca2₁. Optically biaxial with (+) 2V=42-48°, α=1.707±0.003, γ=1.778±0.003, and weakly pleochroic with axial colours X=Y=colorless and Z=light yellow. The hardness is 5.5 (Mohs); cleavage (001) perfect; density=3.62 (measured), 3.87g•cm^-3 (calculated).