The following experiments were carried out with potassium feldspar in order to determine the stability range in temperature and water vapour pressure and to clarify the mechanism of mutual transformation of monoclinic form ((Al, Si) disorder form) and triclinic form ((Al, Si) order form). Under water vapour pressures of 1500, 2400 and 4000 atms. respectively, a natural microcline from Takamizu was treated at various temperatures ranging from 350° to 700°C. for up to 1000 hrs., and was examined if transformation into monoclinic phase took place or not. Under water vapour pressures ranging from 350 to 1000 atms., potassium feldspars were formed by Na-Kion-exchange from the mixture of a natural low albite from Mitsuishi and aqueous solution of potassium chloride, and were examined whether it was monoclinic or triclinic. The stability ranges of monoclinic and triclinic forms were determined from the results of those experiments and summerized in a P. -T. diagram. Taking those results as well as the order-disorder states and the mode of occurrence of potassium feldspars in nature into consideration, it is concluded that most of the naturally occurring potassium feldspars have probably been formed under nonequilibrium conditions and frozen into a metastable phase, and to bring them into the stable phase the catalytic action of water molecules is necessary.

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The crystal structure of linarite was redetermined with Weissenberg photographs newly obtained. Positions of heavy atoms are essentially identical with those reported in the writer's previous paper, but those of light atoms are completely revised.
Copper atom is surrounded by four hydroxyl groups which form an octahedron with two oxygen atoms. Lead atom is situated in an irregular polyhedron formed by seven oxygen atoms and one hydroxyl group.

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Tridymite occurs in the vicinity of Kusatsu Spa as extremely fine crystals in opaline silica which has replaced two pyroxene andesite. Specific gravity: 2.2±0.1, optical properties: n₁ ?? 1.478, n₂ ?? 1.480, 2V ?? 0, elongation negative, showing straight but wavy extinction. Chemical composition: SiO₂ 96.89, TiO₂ 0.86, Al₂O₃ 0.71, Fe₂O₃ tr., FeO none, MnO none, MgO none, CaO none, Na₂O 0.72, K₂O 0.16, H₂O (+) 0.12, H₂O (-) 0.08, P₂O₅ tr., total 99.54%. The d. t. a. curve shows two endothermic peaks, one at 128°C. and the other at 155°C.; they are attributed to the transition from the low to the middle form and from the middle to the high form respectively. Many sharp X-ray powder diffraction lines were confirmed, most of which have not been reported in previous papers. Under the microscope, noticeable texture of the silicified andesite was observed, suggesting that the tridymite has gradually crystallized out of opaline silica: some of its crystals are extremely small and appear to grade into opaline silica.

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Ningyoite occurs extensively in the unoxidized zones of the Ningyôtôgé and the neighbouring uranium deposits as the principal ore mineral. It is a hydrated calcium uranous phosphate with minor amount of various substituting ions, and its chemical formula can be written as Ca_1.0U_0.8R.E._0.2 [P(O, OH)₄]₂•1-2H₂O. Ningyoite is presumed to be comparatively stable, in spite of the similarity of its crystal structure with that of rhabdophane, a meta-stable rare mineral of rare earths, as indicated by their thermal behaviours. Ningyoite contains almost all the rare earths and their abundance ratio resembles that of apatite. This, together with other evidences, strongly suggests that ningyoite was formed by the reaction between apatite and uranium-containing solution.
Ningyoite was synthesized in various conditions from mixtures of uranium-calcium-phosphorus-containing compounds and solutions for the purpose of determining the possible environment of the precipitation of ningyoite. The results of the syntheses from apatite and various uranyl complexes under reducing conditions and the additional experiments indicate that ningyoite is formed only when the excess phosphate ion other than that combined with calcium is contained in solution, and also that the carbonate ion is not favourable for its precipitation. The properties of the synthetic ningyoites are a little variable depending upon the pH values of the solution and other factors, though ningyoite could be formed in a wide range of pH from 1.2 to 7.6 under the reducing condition. Natural ningyoite is considered to have been formed in weakly alkaline condition in comparison with the synthetic minerals.
The nature of the solution from which ningyoite was precipitated in the Ningyô-tôgé area has been considered also from the paragenesis of ningyoite in the uranium ores. Seeing from the fact that the close accociation of ningyoite and such reducing agents as carbonaceous matters and pyrite is common, uranium had probably been transported to the precipitation site in the hexavalent state and was subsequently reduced. The intimate association of ningyoite and gypsum formed by hydration of the original anhydrite indicates that the uranium bearing solution contained sulphate ion as the principal anion, and also that the temperature of the formation of the ningyoite, was above 35°C. The temperature was estimated also by the fact that kaolinite was partly transformed to sericite during the uranium mineralization, to be in the range from 40° to 80°C.

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Djurleite, a new copper sulphide of or about Cu_1.96S composition, is described. Chalcocite-like materials from several localities in Japan and in U. S. A. are identified as the new phase first synthesized by Djurle. The density is 5.63. The X-ray powder data are in complete agreement with those given by Djurle. The symmetry is orthorhombic. The composition is not accurately determined but appears to be approximately Cu_1.96S. Djurleite is found as a primary and secondary mineral associated with one or more of the following mincrals: digenite, bornite, chalcopyrite and pyrite.

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