Baghdadite from Fuka, Okayama Prefecture, Japan

Baghdadite was found in a spurrite zone in skarns at Fuka, Okayama Prefecture, Japan. It occurs as anhedral grains up to 0,5 mm in length and prismatic crystals up to 0.6×0.4×0.2 mm, in association with gehlenite, spurrite, tilleyite, peroéskite, grandite garnet and éesuéianite. The empirical formula of the mineral is (Ca_3.03Na_0.01)_∑3.04(Zr _0.83Ti_0.15)_∑0.98(Si_1.99Al _0.01Fe_0.01)∑_2.01O₉ on the basis of O=9, which is consistent with the ideal formula Ca₃ZrSi₂O₉. The unit cell parameters are a= 10.429(2), b= 10.170(2), c=7.365(1)A and β = 91.01(1)°. The mineral is optically biaxial negatiée with refractiée indices a= 1.735, β= 1.747, and γ= 1.755, and calculated 2 V = 1W. The Vickers microhardness is 803 kg mm² (25 g load) and the density is 3.36 g cm³. It is likely that baghdadite at Fuka was formed by a reaction of pre-existing rankinite and/ or kilchoanite, and ZrO₂ eéoléed from an intrusiée igneous liquid at a high temperature.