The crystal structure of monoclinic subcell (a′=5.534, b′=13.565, c′=25.09Å, β′=93.96°, I2⁄a) of ganophyllite has been determined and refined to an R of 0.078. The structure of true cell (a=3a′=16.60, b=2b′=27.13, c=2c′=50.18Å, β=β′=93.96°, A2⁄a) can be explained based on this average subcell structure. This mineral is a modified layer structure as suggested by Smith and Frondel (1968). The octahedral (sheet) layer is curved like a sine wave along the b-axis and is sandwiched by two tetrahedral layers, each composed of triple chains. The upper and lower chains sandwiching the octahedral layer are always at the outside of the curvature and the small tetrahedral layer is inside. Thus the layer misfit is elegantly minimized in this structure. The interlayer cation is eight coordinated to four oxygens or hydroxyls at the edges of the chains and to four water molecules. The ordering of interlayer cations and water molecules followed by the site preference of aluminum in the tetrahedra, and resultant slight changes in polyhedra of the subcell structure explain why ganophyllite has a large cell. The structural formula of ganophyllite determined from X-ray microprobe and structure analyses is (K, Na, Ca)_x Mn₈(Si, Al)₁₂(O, OH)₃₂(OH)₄·nH₂O, with x=1∼1.5, and n≥4; Z=24 in the true large cell. The average monoclinic subcell structure also can explain the structure of triclinic polytype recently found by Jefferson (1978).

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One dimensional refinement and infrared OH band investigation have been made on five orthochlorites of the Mg–Fe series and on two Mg-leptochlorites with substitution of 2Al for 3Mg. The results indicate that the leptochlorites have cation vacancies in the interlayer sheet. Octahedral Al is concentrated in the interlayer sheet in every sample, but considerable amounts of Al are contained also in the 2: 1 octahedral sheet in the Al- and/or Fe-rich chlorites, which suggests a relatively narrow layer charge range in chlorites. The variation of cation composition of the tetrahedral and octahedral sheets results in variation of the sheet thickness and the interlayer O–OH space: with increasing tetrahedral Al (generally octahedral Al also increases), the two octahedral sheet thicknesses and the O–OH space decrease, but the tetrahedral sheet thickness increases; larger Fe²⁺ content brings about thicker octahedral and thinner tetrahedral sheets and smaller O–OH space.
The O–OH space, which primarily determines the d(001) spacing, is concluded to be controlled by both the surplus negative charge of 2 : 1 layer surface oxygens and the interlayer octahedral cations; the former is caused by the tetrahedral Al substitution for Si and is affected also by the 2 : 1 octahedral cations. The OH bands and tetrahedral ordering of amesite and the O–OH spaces of dioctahedral chlorites and of some 1 : 1 layer silicates are discussed along with those of trioctahedral chlorites.

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Fine intergrowth of diopside and pigeonite in a subcalcic diopside megacryst from Monastery kimberlite pipe has been studied by the lattice image technique of high resolution electron microscopy. The common plane of the intergrowth is approximately (001), and the average widths of diopside and pigeonite lamellae are about 100 and 50Å, respectively. The interfaces are coherent and sinusoidally modulated along the common a axis. The lattice fringes continuously curved along each c axis around the interfaces suggest a gradual compositional change in both phases.
The characteristics of the lattice images of the intergrowth indicate the following formation process of the diopside megacryst: the megacryst should have grown as a C2⁄c single crystal and spinodal decomposition into Ca-rich and Ca-poor regions with C2⁄c resulted in a lamellae texture, and then, the Capoor region, high pigeonite, was transformed to low P2₁⁄c pigeonite, forming the antiphase domains.

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