Abstract: Takedaite, Ca₃B₂O₆, has been found in crystalline limestone near gehlenite-spurrite skarns at Fuka, Okayama Prefecture. It occurs as aggregates of granular crystals up to 0.8 mm long and 0.3 mm wide. The mineral is associated with nifontovite, olshanskyite, pentahydroborite, frolovite, sibirskite, calcite and an unidentified mineral, is white or pale gray, and has a vitreous luster. Takedaite is trigonal with space group of R3¯c, a = 8.638(1), c = 11.850(2)Å, Z = 6. The strongest lines in the X-ray powder pattern [d in A(I)(hkl)] are 2.915(100)(113), 1.895(75)(223), 2.756(61)(104), 2.493(44)(300), 2.044(21) (214,131), 2.160(19)(220), 1.976(18)(006), 1.549(12)(306). The Vickers microhardness is 478 kg mm⁻² and the Mohs hardness 4.5. The density is 3.10(2) g cm⁻³ (meas.) and 3.11 g cm⁻³ (calc.). Wet chemical analyses give the values CaO 71.13%, B₂O₃ 28.41%, ig. loss 0.14%, and total 99.68%. The empirical formula calculated on the basis of O = 6 is Ca_3.053B_1.965O₆, with the simplified formula of Ca₃B₂O₆.