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 (Ca3.03Na0.01)Σ3.04(Zr0.83Ti0.15)Σ0.98(Si1.99Al0.01Fe0.01)Σ2.01O9 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)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 2V=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 ZrO2 evolved from an intrusive igneous liquid at a high temperature.
We report an occurrence of extremely low-alumina orthopyroxenes in a spinel lherzolite from the Horoman Peridotite Complex, Japan. The low-Al orthopyroxenes occur in two modes; the first occurs at the margin of a large orthopyroxene porphyroclast in contact with olivine and the second occurs at grain boundaries between clinopyroxene and olivine. Al2O3, Cr2O3 and CaO contents in the low-Al orthopyroxenes are less than 0.2 wt.% and are distinctively lower than those in orthopyroxene porphyroclasts. Petrographic observations combined with a inferred P-T history of the Horoman peridotite reveal that the low-Al orthopyroxenes were formed through a very local reaction between peridotite with aqueous fluids, which were not pervasively altering the precursor mineralogy.
A series of experiments provided data on the forsterite-monticellite solvus under a pressure of 1 atm and in the temperature range of 1100 to 1450°C. The forsterite-monticellite solvus is asymmetric as shown in the previous study. Margules type of the excess energy is expressed by Gex=XMgM2XCaM2(XCaM2WMgCa+XMgM2WCaMg), where the asymmetric Ca-Mg mixing model yielded as WCaMg=36.32±0.34 (unit in kJ), WMgCa=32.72±0.32, whereas the symmetric Ca-Mg mixing model resulted as WCaMg=WMgCa=34.05±0.22. The asymmetric Ca-Mg mixing model fits well with the data of the forsterite-monticellite solvus. The present results are consistent with the previous analyses of miscibility gaps in Ca-Mg olivines, and the deviation from the ideality of Ca-Mg mixing is slightly smaller than the previous estimates. Compared with the previous data, the solvus becomes narrow with the increase of pressure. The negative excess volume of Ca-Mg olivine solid solution causes this character, but the pressure effect on the solvus is small.
The crandallite, beudantite and alunite (jarosite) mineral groups are reviewed, with an emphasis on the evaluation of their suitability as storage materials for toxic metals. New data on the highly flexible crystal chemistry, crystallography and thermodynamic stability fields of both natural and synthetic members are summarised and critically discussed. These compounds can safely incorporate a large number of toxic and radioactive metals. Extensive solid solubilities have been observed. The majority of the members are characterised by very low solubilities over a wide range of pH and Eh conditions, and by high temperature stabilities (up to 400-500°C). It is suggested, also by comparison with other mineral waste hosts (apatites, pyrochlores), that these materials can be favourably used for the long-term fixation and immobilisation of toxic ions of elements such as As, Pb, Bi, Hg, Tl, Sb, Cr, Se, and of radioactive isotopes of K, Sr, Th, U and REE.