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, perovskite, grandite garnet and vesuvianite. The empirical formula of the mineral is (Ca
3.03Na
0.01)
Σ3.04(Zr
0.83Ti
0.15)
Σ0.98(Si
1.99Al
0.01Fe
0.01)
Σ2.01O
9 on the basis of O=9, which is consistent with the ideal formula Ca
3ZrSi
2O
9. The unit cell parameters are
a=10.429(2),
b=10.170(2),
c=7.365(1)Å and β=91.01(1)°. The mineral is optically biaxial negative with refractive indices α=1.735, β=1.747, and γ=1.755, and calculated 2
V=78°. The Vickers microhardness is 803 kg mm
−2 (25 g load) and the density is 3.36 g cm
−3. It is likely that baghdadite at Fuka was formed by a reaction of pre-existing rankinite and/or kilchoanite, and ZrO
2 evolved from an intrusive igneous liquid at a high temperature.
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