A new 20-layered polytype of CdI₂ was discovered, and its crystal structure was determined. This structure is represented as (11)₅211222 with unit-cell dimensions a=4.24Å, c=68.4Å, and space group P3m1. A new type of partial diffraction enhancement of symmetry was observed in X-ray diffraction pattern of this polytype.

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The z parameters of atomic planes in two sudoites and one regularly interstratified sericite/sudoite from Kuroko deposits have been refined using 00l X-ray reflections. The results indicate that the interlayer O–OH space is similar to, but the dioctahedral 2 : 1 layer thickness is thinner than in trioctahedral chlorites. The octahedral cation number in the interlayer sheet is a little less than 3.0 atoms. A structural formula [Mg_1.3Al_1.5(OH)₆]^1.1+[(Mg_0.3Al_1.7)(Si_3.2Al_0.8)O₁₀(OH)₂]^1.1− is suggested for the sudoite from the X-ray, chemical, and thermogravimetric data. The fit of the dioctahedral and trioctahedral sheets seems to be explained by the chemical composition of the two sheets.
The interstratified sericite/sudoite gives hkl reflections, which have been indexed in terms of an orthohexagonal cell (b=9.02₄, c=24.14Å). A stacking sequence composed of 1 M or 2 M₁ mica and IIb chlorite layer types has been found on the basis of the 20l intensities.

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Bicchulite was synthesized from gehlenite solid solutions with a composition range from Ak₀Ge₁₀₀ to Ak₄₀Ge₆₀. Upper limits of the stability field of bicchulite at 1 kbar water pressure were found to be at 635°C for Ak₀Ge₁₀₀, 610°C for Ak₂₀Ge₈₀, and 605°C for Ak₄₀Ge₆₀. Gehlenite with the akermanite components less than 20% decomposes to bicchulite±idocrase±xanthophyllite below the temperature of the stability limit, while gehlenite with the akermanite component more than 30% breaks down at a temperature higher than the temperature of bicchulite stability, 630°C for Ak₃₀Ge₇₀ and 680°C for Ak₅₀Ge₅₀, forming idocrase+xanthophyllite±monticellite. Xanthophyllite obtained in the experiments is stable only at temperatures above about 400°C. Below that temperature it changes to hydrogrossular.
Some natural specimens were also studied for geological applications.

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Crystal structure of sugilite has been refined by the least squares method using 435 reflections measured on an automated single crystal diffractometer using MoKα radiation. The final unweighted R-factor is 0.047 for 429 reflections. The cell dimensions are: a=10.007(2), c=14.000(2)Å; space group P6⁄mcc. Sugilite is isostructural with milarite group minerals, and can be described as (K_0.81Na_0.19)^[12] (H₂O_0.91Na_0.64)₂^[9] (Fe³⁺_1.32Na_0.59Ti⁴⁺_0.06Fe²⁺_0.03)₂^[6] (Li_2.12Al_0.59Fe³⁺_0.29)₃^[4]Si^[4]₁₂O₃₀ with Z=2 by structure formula of milarite group defined by Forbes, Baur and Khan (1972). The SiO₄ tetrahedra from hexagonal double rings with the composition Si₁₂O₃₀. These double rings are linked by Li, Al and Fe³⁺ atoms in tetrahedral four-coordination to form a tetrahedral frame structure. Na and H₂O are located in nine-coordinated sites.

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The crystal structure of shattuckite (Cu₅(OH)₂(SiO₃)₄), space group Pcab, a=9.88, b=19.82, c=5.40Å, Z=4, has been investigated by three dimensional intensity data. The newly determined structure is the same as the structure studied by Evans and Mrose (1966) and Le Bihan (1967) in the projection parallel to the c-axis, but the z-parameters of silicon, copper and oxygen atoms are different. The configuration of the nearest neighbours of copper atoms are also different. The copper atoms stay at the centers of the rectangles of oxygen atoms, showing the usual coordination of Cu²⁺ in copper bearing minerals in general.

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