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

Abstract

Parasibirskite, with the ideal formula Ca2B2O5·H2O, is a new mineral species found at Fuka, Okayama Prefecture, Japan. It is a polymorph of sibirskite, CaHBO3, and occurs as subparallel aggregates of tabular crystals up to 40 × 20 × 3 µm in size. Associated minerals are takedaite, olshanskyite, sibirskite, frolovite and calcite. The mineral is white, and has a weak pearly luster. Optically, the mineral is biaxial positive, α 1.556(2), β 1.593(2), γ 1.663(2) (λ 589 nm). The Vickers microhardness of aggregates is 121 kg mm−2. The mineral is monoclinic with space group of P21/m, a 6.722(4), b 5.437(2), c 3.555(2) Å, β 93.00(5)°, V 129.8(2), Å3. The strongest lines in the X-ray powder pattern [d in Å (I)(hkl)] are 2.237(100)(300), 6.73(70)(100), 2.975(60)(011), 3.354(30)(200), 2.855(20)(210) and 1.776(20) (002). Wet chemical analysis, electron-microprobe analysis and ICP emission spectrometry give the values CaO 56.06 %, B2O3 34.10 %, H2O 9.97 % and total 100.13%. The empirical formula calculated on the basis of O = 6 is Ca1.985B1.945O4.901·1.099H2O, for Z = 1, Dcalc 2.54 and Dmeas 2.50(1) g cm−3. Parasibirskite is formed by hydrothermal alteration of takedaite.

Inyoite from Fuka, Okayama Prefecture, Japan

“…At the Fuka mine, calcium borate minerals such as olshanskyite, nifontovite (Kusachi and Henmi, 1994), takedaite , frolovite , and parasibirskite (Kusachi et al, 1998) have been found in an irregular body up to 3 m long and 2 m wide in the crystalline limestone near the gehlenite spurrite skarns. During the present study, a new occurrence of the calcium borate minerals was also found at the same mine, where nifontovite and pentahydroborite occur abundantly as composite minerals in an irregular body up to 7 m long and 3 m wide in the crystalline limestone in the vicinity of the skarns.…”

Crystal structure of parasibirskite (CaHBO3) and polymorphism in sibirskite and parasibirskite

“…A series of calcium borate and calcium borate hydroxide minerals such as takedaite, sibirskite, parasibirskite, uralborite, nifontovite, olshanskyite, frolovite, and pentahydroborite were discovered at Fuka, Okayama Prefecture, Japan Kusachi et al, , 1995Kusachi et al, , 1997Kusachi et al, , 1998Kusachi et al, , 1999Kusachi et al, , 2000. These are hydrothermal alteration products of takedaite, and the concentration of H 2 O varies with the formation temperature, as discovered by Hart and Brown (1962) from the hydrothermal synthesis of calcium borate compounds.…”

“…These are hydrothermal alteration products of takedaite, and the concentration of H 2 O varies with the formation temperature, as discovered by Hart and Brown (1962) from the hydrothermal synthesis of calcium borate compounds. Parasibirskite, CaHBO 3 , a new mineral, is a dimorph of sibirskite that was first reported in Fuka by Kusachi et al (1998). The crystal structure of sibirskite was determined using Monte Carlo calculations by Miura and Kusachi (2008).…”

“…However, the crystal structure of parasibirskite has not yet been clarified and the crystallographic relationship between these dimorph minerals is not known. In the present study, a Monte -Carlo -based simulation developed by Miura and Kikuchi (1999) is employed to solve an initial model for the crystal structure of parasibirskite using a set of d -values and intensity data reported by Kusachi et al (1998).…”

The role of aqueous silica concentration in controlling the mineralogy during high temperature contact metamorphism: A case study from Fuka contact aureole, Okayama, Japan

“…Ten new minerals were discovered from this occurrence. They are bicchuite (Henmi et al, 1973), fukalite (Henmi et al, 1977), oyalite (Kusachi et al, 1984), henmilite (Nakai et al, 1986), clinotobermerite (Henmi and Kusachi, 1992) morimotoite , kusachiite (Henmi, 1995), takedite , parasibirskite (Kusachi et al, 1998), and okayamalite (Matsubara et al, 1998). Five of these new minerals are calcium boro silicates.…”