An alkali amphibole crystal on a thin section of nepheline syenite from Poços de Caldas, Brazil is examined using an elliptically polarizing microscope equipped with a mercury lamp as a light source and a pair of rotatable quarter wave plates placed in the optical path. The nature of the light transmitted through the crystal is revealed to be an elliptically polarized light with an ellipticity of 0.23. This result is concordant with the works of T. Shoda (1957; 1958; 1961), who revealed the existence of elliptically polarized light not only in optically active crystals but also in some absorbing crystals. The difference between the nature of the elliptically polarized light resulting from absorption and that due to optical activity is discussed.
Inyoite was found as fissure fillings in calcium borate minerals, which occur as an irregularly shaped body in the crystalline limestone near the gehlenite-spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. Inyoite occurs as aggregates of tabular crystals up to 1 mm wide, and rarely as euhedral crystals up to 0.5 mm wide in fissures of calcium borate minerals such as nifontovite, pentahydroborite, sibirskite and parasibirskite. The fissure fillings are composed only of inyoite. This is the first finding of inyoite in Japan. The type of occurrence is also different from those in many other localities in the world. Electron microprobe and CHNS / O analyses gave the empirical formula Ca1.99B5.96O5.92(OH)10·8.08H2O on the basis of O = 24. The unit cell parameters are a = 10.616(2), b = 12.068(1), c = 8.404(1) Å and β = 114.01(1)°. The mineral is optically biaxial negative with refractive indices α = 1.492, β = 1.506 and γ = 1.517, giving a calculated 2V = 82°. The Vickers microhardness is 91 kg mm−2 (10 g load) and the Mohs hardness number is 2.5. The measured density is 1.875 g cm−3. It is likely that the inyoite at the Fuka mine was formed by a reaction of ground water with calcium borate minerals at a temperature of around 20°C.
Based on breathing-shell-model MD simulations with quantum correction, we calculated the temperature-pressure-volume (T-P-V) equation of state(EOS) of γ-Mg2SiO4 to be used as a reliable pressure calibration standard at temperatures up to 2000 K and pressures up to 25 - 30 GPa. The simulations use empirical interionic potentials, previously developed for the Mg2SiO4 system to reproduce accurately measured structural and elastic properties. The potentials are applicable not only to γ-Mg2SiO4, but also to α- and β-Mg2SiO4 over wide temperature and pressure ranges. We assessed the accuracy of the resulting T-P-V EOS of γ-Mg2SiO4, by using the recently reported data on simultaneous X-ray measurements of MgO and γ-Mg2SiO4, performed by using synchrotron radiation in a multi-anvil apparatus at high temperatures and pressures. We found that pressures estimated through the MgO EOS presented by Matsui et al. (2000) and those for the γ-Mg2SiO4 EOS agree very well, with the average differences in the estimated pressures between the two EOS’s less than 0.3 GPa at T between 1500 and 2000 K and P between 19 and 23 GPa.