Magnesiorowlandite, Y4(Mg,Fe)(Si2O7)2F2, a Mg–analogue of rowlandite–(Y), was found in a pegmatite at Souri Valley, Komono, Mie Prefecture, central Japan. The mineral occurs as aggregates composed of gray massive and white powdery parts. The aggregates are up to 1 cm in diameter scattered in the pegmatite. The mineral is associated with quartz, albite, K–feldspar, muscovite, allanite–(Ce), gadolinite–(Y), and ‘yftisite–(Y)’. It is transparent and gray to white in color with a vitreous to oily luster. The streak is white and cleavage is not observed. The Mohs hardness is 5 to 5½. The calculated density is 4.82 g/cm3. It is biaxial negative and refractive indices are α = 1.755 (5) and γ = 1.760 (5) with non–pleochroism. Electron microprobe (WDS) analysis gave SiO2 28.61, FeO 2.94, MnO 0.35, MgO 2.77, CaO 0.03, Y2O3 36.02, La2O3 0.29, Ce2O3 2.64, Pr2O3 0.64, Nd2O3 4.72, Sm2O3 2.82, Gd2O3 4.45, Tb2O3 0.69, Dy2O3 4.87, Ho2O3 0.50, Er2O3 1.64, Tm2O3 0.34, Yb2O3 2.02, Lu2O3 0.69, ThO2 0.24, F 4.56, –F2=O 1.92, total 99.91 wt% (average of 16 analyses), and led to the empirical formula, (Y2.71Nd0.24Dy0.22Gd0.21Ce0.14Sm0.14Yb0.09Er0.07Pr0.03Tb0.03Lu0.03Ho0.02Tm0.02La0.01Ca0.01Th0.01)∑3.98(Mg0.58Fe0.35Mn0.04)∑0.97Si4.00O13.97F2.03 on the basis of O + F = 16. The mineral is triclinic, P1, a = 6.527(6), b = 8.656(9), c = 5.519(5) Å, α = 99.09(8), β = 104.17(7), γ = 91.48(8)°, V = 297.9(5) Å3, Z = 1. It is non–metamict, and the strongest lines in the powder XRD pattern [d(Å) (I/I0) hkl] are 4.95 (33) 110; 3.64 (37) 021; 3.54 (38) 111; 3.08 (100) 201, 021; 2.92 (26) 211, 210; 2.68 (32) 112; 2.65 (26) 130, 012, 002; 2.63 (28) 220. The crystal structure was determined and refined to R1 = 0.0736 for 1645 reflections with I > 2σ(I) of single crystal XRD data. In the crystal structure, the Si2O7 group, together with (Mg,Fe)O4F2 octahedron, connects the 7–coordinated and 8–coordinated REEs polyhedra to form the 3–dimensional structure.
The temperature–dependence of the lattice parameters, unit cell volume and the thermal expansion tensor of petalite (LiAlSi4O10) have been determined from high resolution, time–of–flight powder neutron diffraction data collected at ninety temperatures between 4.2 K and 600 K. At low temperatures, after a short saturation interval, the unit cell volume decreases from 424.114(6) Å3 at 15 K, reaching a minimum of 423.470(6) Å3 at 219 K, before slowly increasing to 425.004(7) Å3 by 600 K. Petalite may be considered to be a further example of a low expansion material (defined as having a coefficient of linear thermal expansion of less than 2 × 10−6 K−1) in the well–studied Li2O–Al2O3–SiO2 system, however in this case, this technologically useful property is found to occur at low temperatures, in the interval 157 K to 298 K. From the temperature variation of the unit cell parameters, the eigenvalues (λii) and eigenvectors of the thermal expansion tensor have been calculated for the range 20 K to 600 K. The eigenvalue (λ22) associated with the unique monoclinic axis (b) is positive for all temperatures above saturation, ~ 50 K, and reaches a maximum value of 1.42 × 10−5 K−1 at 600 K. In the a–c plane, above the 20 K saturation temperatures, λ11 changes sign, negative to positive at 232 K, and λ33 is always found to be negative, but reducing in magnitude with increasing temperature. The orientation of λ11 is found to be approximately parallel to a, and λ33 is approximately parallel to c* at all temperatures. The 600 K thermal expansion coefficients associated with these two principal axes is of the order of four times smaller than that associated with λ22 (λ11: 3.2 × 10−6 K−1; λ33: −3.4 × 10−6 K−1). Between 20 K and 232 K, the thermal expansion tensor is therefore represented by a hyperboloid of two sheets, and above this temperature, the representation quadric changes to a hyperboloid of one sheet. The orientation of the principal axes in (010) is continuous through the change in the representation quadric, and only shows a small variation throughout the temperature interval 20 K to 600 K.
Graphite–3R was found at an outcrop in Kanayamadani, central Japan that had green–black jadeitite, altered jadeitite, and fracture zones in serpentine mélange. The graphite from the three zones was characterized using polarizing microscopy, XRD, Raman spectroscopy, SEM, HRTEM, and stable carbon–isotope mass spectrometry. Graphite in the black jadeitite zone is possibly crystallized simultaneously with prehnite in the stability field of prehnite (P <0.6 GPa and at T = 150–420 °C). The δ13C of graphite in the black jadeitite zone ranged from −8.570‰ to −7.870‰, suggesting that it does not have an organic origin. The graphite of the black jadeitite zone was possibly formed in CO2–CH4 rich fluid. XRD, Raman spectroscopy, and HRTEM observations suggested that the altered jadeitite zone had both low and high crystalline graphite. The altered jadeitite zone was located at the outer region of the green–black jadeitite zone and penetrated by many prehnite veins during a later stage. Amorphous carbon and graphite–3R found from the fracture zone may have formed as a result of graphite–2H crushing during fault movement between green–black and altered jadeitite zones. Changes in the crystal structure and detailed mineralogy of graphite can effectively be used to study tectonics and are key to understanding tectonic movement in geological processes.
This paper describes textures and chemical compositions of alkali feldspars to get a clue of the cooling history of the Kakkonda granitic pluton. The Kakkonda pluton of tonalite–granodiorite contains two types of alkali feldspar: one is microperthitic alkali feldspar in the lower–temperature granodiorite of 370 °C at the shallower depth (sample C11, 2936–2939 m) and the other is non–microperthitic alkali feldspar in the higher–temperature tonalite over 500 °C at the deeper depth (sample C13, 3726–3729 m). The two types of alkali feldspars were examined using an electron microprobe analyzer with an attached cathodoluminescence spectrometer system. The former alkali feldspar is spotted due to microscopic pores and several types of inclusions with microperthitic texture, and the latter is clear and featureless under a microscope. Concentric and/or domain Ba zoning patterns with irregular veins were newly found in both the alkali feldspars. The microperthitic texture in the lower–temperature granodiorite contains two types of Ab–rich plagioclase: one is a bead type of smaller size with rather rounded shape, and the other is a flake type of larger size with irregular shape. The appearance of the microperthitic alkali feldspar is quite different from ordinary patch microperthites with turbidity in granitic rocks described to date. Based on the microperthitic textures and Ba–distribution patterns, resorption of primary plagioclase during the growth of interstitial alkali feldspar might contribute to the formation of the microperthitic alkali feldspar in the granodiorite of C11. Barium–zoning patterns are principally magmatic (C13 alkali feldspar), but they were modified during the formation of microperthite (C11 alkali feldspar) at cooling.
This study examines the intensity drops (‘negative peak’, ‘hole’, or ‘background hole’) in the X–ray spectra of a wavelength–dispersive spectrometer with a pentaerythritol (PET) analyzing crystal. The PET crystal in the (002) orientation has a total of thirty three possible hole locations in the range 25° < 2θ < 125°. Eight of these were observed experimentally at 2θ = 31.053°, 31.262°, 38.302°, 38.937°, 43.493°, 45.264°, 59.161°, and 69.564° using an electron probe microanalyzer. It is important to ascertain the background intensity profile around each hole by wavelength scanning on a given spectrometer because, like the characteristic peaks, the shape and magnitude of holes depend on the specific spectrometer characteristics.