Takedaite, a new mineral from Fuka, Okayama Prefecture, Japan

Abstract

Takedaite, Ca3B206, has been found in crystalline limestone near gehlenite-spurrite skams 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 R3c, a = 8. 638(1), c = 11.850(2)A, Z = 6. The strongest lines in the X-ray powder pattern [d in A (/) (hkl)] arc 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 gcm -3 (calc.). Wet chemical analyses give the values CaO 71.13%, B203 28.41%, ig. loss 0.14%, and total 99.68%. The empirical formula calculated on the basis of O = 6 is Ca3.053BL96506, with the simplified formula of Ca3B206.

Calciborite from the Fuka mine, Okayama Prefecture, Japan

“…On the other hand, takedaite, Ca 3 B 2 O 6 , which discovered at the Fuka mine, is anhydrous mineral as well as calciborite. Kusachi et al (1995b) described that takedaite would appear to be formed at a temperature around 250 °C based on the result of synthetic experiment by Schäfer (1968a). In view of these results, calciborite from the Fuka mine would therefore crystallized at a temperature between 250 and 300 °C.…”

Priceite from the Fuka mine, Okayama Prefecture, Japan

“…Kusachi et al (1995) described that takedaite would appear to be formed at a temperature around 250°C. It is possible to postulate that shimazakiite also formed around 250°C.…”

Crystal forms of borate minerals from the Fuka mine, Okayama Prefecture, Japan

“…2 4 2 50 cm 120 cm , 7 mm ( 1982; Nakai et al, 1986) 3 20 cm 50 cm (Kusachi et al, 2000) 4 2 m 3 m 1.5 mm (Kusachi and Henmi, 1994;Kusachi et al, 1995b;etc. ) 3 mm 8 cm 4 3 m 7 m (Kusachi et al, 2004) mm cm 1 cm…”