Many materials exhibit topotaxy in the processes of phase transformations and these pro-cesses appear from X-ray diffraction patterns to be changes from single crystals to other single crystals. It is, therefore, possible to study processes of topotactic phase transformations by X-ray single crystal diffractometry. A four-circle diffractometer and its software system, suitable to measure intensity distribution of one dimensional region in the reciprocal space simultaneously, have been developed in order to study topotactic phase transformations. The difractometer was constructed with a combination of a white X-ray source and a Si (Li) solid state detector. The software system was made to suit these combination. Examples of measurements by the system were also given.

抄録全体を表示

Hingganite, hellandite and wodginite occur in druse type pegmatite in quarries at Tahara, Hirukawa-mura, Ena-gun, Gifu prefecture, Japan. Two kinds of hingganite, (Y_1.22Ca_0.26…)_Σ1.91Fe²⁺_0.09Be_2.08Si_2.08O_8.09(OH)_1.91 and (Ce_0.54Y_0.51Nd_0.31…)_Σ2.08Fe²⁺_0.41Be_1.96Si_1.96O_8.87(OH)_1.13, were found as colorless (hingganite-(Y)) to light brown (hingganite-(Ce)) euhedral crystals associated with quartz, feldspar, mica, cassiterite, stokesite, flourite, chlorite, sphene, and an unknown mineral chemically related to hingganite. Hellandite, (Ca_5.75Y_3.70Nd_0.24Dy_0.21…)_Σ10.65 (AI_1.45Mn_0.25Ti_0.21Fe_0.11) (OH)₄[Si₈B₈O_40.22(OH)_3.78] occurs as an aggregate of colorless transparent crystals covering surface of hingganite. The associated minerals of hellandite are quartz, flourite, chlorite and zeolite group minerals. Wodginite, Mn_3.84 (Sn_1.53 Ti_1.11Fe³⁺_0.60W_0.31Ta_0.27Zr_0.18) (Ta_7.99Nb_0.01)O₃₂ occurs as a black prismatic crystal on feldsper, associated with quartz, mica, topaz, beryl, flourite. The chemical compositions and X-ray crystallographic data of these minerals are given and are compared and discussed with data previously reported. Lattice parameters: Hingganite-(Ce), monoclinic, a=9.996(10), b=7.705 (7), c=4.792(4) Å, β=90.06(4)°; Hellandite, monoclinic, a=18.91(2), b=4.684(6), c=10.30(6) Å, β=111.7(1)°; Wodginite, monoclinic, a=9.513(9), b=11.456(12), c=5.108(4) Å, β=91.09(9)°.

抄録全体を表示

Experimental techniques for calorimetry at 700-800°C using a Calvet-type microcalorimeter are described. This method is applied to solution calorimetry in molten oxide solvents to measure the enthalpies of formation of silicates and related minerals, the enthalpies of phase transitions, and the enthalpies of mixing in solid solutions. The accurate measurements are made using the small amounts of sample (about 200 mg total). The enthalpies of high-pressure phase transition of silicates are used to calculate the equilibrium phase relations at high pressures and high temperatures.

抄録全体を表示

Thermodynamic properties of mantle minerals, involving olivine, pyroxenes, spinel and garnet are critically reviewed on the basis of the theory of the single- and multi-sited solid solutions. The activity-composition relationships of these minerals are given. Regular solution models are sufficient to describe thermodynamic properties of olivine and garnet. Pyroxenes behave as the multi-sited solutions. The microscopic model shows that pyroxenes are macro-scopically regular solutions with positive excess free energies of mixing. By the application of these thermodynamic models to mantle minerals involving olivine, orthopyroxene and garnet, equlibration pressures an temperatures of garnet lherzolites are calculated.

抄録全体を表示