Chemical compositions of natural iron-wollastonites formed at low temperatures thus far available are in the region of about (Ca_0.83Fe_0.17)SiO₃, and those of ferroan wollastonites have less iron content than about 5 mole % FeSiO₃. In this paper close associations of iron-wollastonite and wollastonite from the Sampo and Ohminé mines are described. Studies by EPMA and thermal experiments on the pairs make it clear that there is an immiscibility gap between iron-wollastonite and wollastonite at low temperatures.

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Mössbauer spectra of six natural olivines and their annealed equivalents have been measured at several temperatures up to 426°C. Four of the unannealed olivines of plutonic or metamorphic origin exhibit relative enrichment of Fe²⁺ in M1 whereas two olivines of volcanic origin exhibit preferential ordering of Fe²⁺ in M2. The quadrupole splitting (Δ) of Fe²⁺ in the M1 site is less than that of Fe²⁺ in the M2 site. Δ of M1 and M2 decrease linearly as a function of absorber temperature (T), with d(Δ_M1)/dT more negative than d (Δ_M2)/dT. This result is similar to that obtained by Brown and Prewitt (1973) who found that distortion of the M1 octahedron increases at a faster rate than that of M2 with rising crystal temperature. Our data also indicate that Δ of the M1 and M2 sites decrease and increase, respectively, with increasing Fe²⁺ content of M1, suggesting increased distortion of the Ml octahedron with increasing Fe²⁺ content. Isomer shifts (δ) at both sites show similar decreases with increasing absorber temperature and are not significantly affected by changes in Fe²⁺ content at either site. The slightly larger δ of the M2 site suggests that M2-O bonds are more ionic than M1-O bonds. The results of annealing experiments indicate that the Mg/Fe exchange reaction between the Ml and M2 sites is not as sluggish as previously reported by Virgo et al. (1972).

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Two polymorphs of MnSiO₃, pyroxmangite and rhodonite, were examined with the conventional hydrothermal technique. Pyroxmangite was synthesized in the temperature lower than about 700°C and rhodonite in the higher temperature. Synthetic and natural pyroxmangites transform into rhodonite at about 700°C as temperature rises. However, the reverse reaction from rhodonite to pyroxmangite were tried but no transformation was recognized by the X-ray diffraction technique.
The crystallization processes of MnSiO₃ were investigated using three different starting materials under a water pressure of 2kb. In the crystallization of pyroxmangite, at 650°C, a clinopyroxene-like phase appeared as an intermediate phase, changes to pyroxmangite which further transforms into rhodonite at 750°C.
Structural changes in the transformation of pyroxmangite to rhodonite with rising temperature or increasing duration time may be regarded as a decrease of the number of silica tetrahedra in a repeat unit of a single chain. There seems to be the same relationship among clinopyroxene and pyroxenoids, when clinopyroxene is regarded as a kind of pyroxenoid having a side-step after an infinite repetition of two silica tetrahedra unit along the single chain.

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The possible structure types derived from the Pbca-orthopyroxene are shown. There are sixteen space groups, as subgroups of Pbca, without destroying the original unit-cell type setting. Five structure types have two kinds of tetrahedral chain, nine types have four kinds of tetrahedral chain and two types have eight kinds of tetrahedral chain, respectively.

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The surface structures of (0001) and (000^-1) faces of single crystals of A1N grown by the sublimation method were observed and classified in relation to the piezoelectric effect. The piezoelectric effect bears a relation with the surface structures of blade-shaped crystals and part of tabular crystals. The surface which is charged positively by a compressive stresss in the direction parallel to the c-axis is defined as the (000^-1) face. The surface which is charged negatively by the same stress is defined as the (0001) face. On the (000^-1) face, hexagonal growth hillocks and bunched growth steps were observed and on the (0001) face, only irregular thin growth layers or flat faces without any characteristic features were observed. It can be concluded therefore that the growth rate normal to the (000^-1) face is larger than that normal to the (0001) face. Most of the tabular crystals do not show the difference in the surface structure. Some of them have the surface structure characteristic of the (0001) on both surfaces and other crystals have the surface structure characteristic of the (000^-1) on both surfaces. It is concluded that these crystals have interstice lattice stacking faults in the basal planes due to the formation of Al₂CO. In fact, no piezoelectric effect was observed on these crystals.

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A joaquinite-like new mineral was found from Ohmi, Niigata Prefecture, Central Japan in 1971. Chemical analysis gave, in weight %, SiO₂ 35.12, Nb₂O₅ 1.42, TiO₂ 12.48, A1₂O₃ 0.27, REE₂O₃ 1.12, FeO 4.75, CaO trace, SrO 5.85, BaO 31.31, ZrO 0.19, MgO 0.03, Na₂O 2.74, K₂O 0.94, MnO trace, H₂O+2.59, H₂O-0.47, total 99.36, corresponding to
(Na_0.97K_0.03)_1.00(Ba_2.76Sr_0.76Na_0.23^*RE_0.12Fe⁺³_0.12Mg_0.01)_4.00(Fe³⁺_0.79^**Nb_0.13Ti_0.l3Zr_0.02) _1.07Ti_2.00(Si_7.94Al_0.06)_8.00O_24.66(OH)_3.02
^*RE wt.=100 ^**Ta₂O₅=0
The precession photographs show this mineral to be orthorhombic with a 9.777±0.005Å, b 10.517±0.006 Å, c 22.392±0.12Å, and possible space guoup Pcam or Pca2₁. Optically biaxial with (+) 2V=42-48°, α=1.707±0.003, γ=1.778±0.003, and weakly pleochroic with axial colours X=Y=colorless and Z=light yellow. The hardness is 5.5 (Mohs); cleavage (001) perfect; density=3.62 (measured), 3.87g•cm^-3 (calculated).

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Cell dimensions of boltwoodite, K(H₃0)(UO₂)(Si0₄)•O-1H₂O, have been determined using electron and X-ray powder diffraction data: a 13.71(1), b 7.14(1), c 12.35(2)Å, β 102.1(1)°, V 1187(3)A³. Z=6. G_meas.=3.6, G_calc.=3.52(0H₂O)-3.68(1H₂O). The newly indexed X-ray powder data for sklodowskite and kasolite are given.

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