Microprobe analyses of optically homogeneous detrital biotites from sandstones of the Visingsö Group and the Dala Sandstone, Sweden, revealed a consistently low K content (generally <0.75 atom/formula unit) and variable amounts of Fe, Mg, Al, and Si. Electron probe profiles of some biotite grains indicated two major types of interstratification, one consisting of mainly illite layers and the other apparently consisting of chlorite layers. The layer thicknesses commonly ranged between 0.5 and 3 μm. Microprobe analyses of some thick (∼5 μm) illitic layers indicated a phengitic composition, wherein the mica was relatively rich in octahederal Fe and Mg. The chloritic layers appeared to be Fe-Mg-rich and generally had octahederal totals of <6 atom/formula unit. Variations in the chemical composition of the biotite and some of the illite and chlorite were probably due to an uneven distribution of small amounts of the interstratified phases. The illite and chlorite layers were apparently formed by pseudomorphic replacement of detrital biotites, i.e., gradual replacement of one biotite layer by one layer(s) of illite and/ or chlorite during diagenesis.

Cronstedtite from Lostwithiel, Cornwall, England, in which two polytypic groups (A and C) are present within the same crystal, has been investigated using various techniques to reveal the distribution of the two groups and the relationship between polytypic structure and chemical composition. X-ray precession photographs from cleaved fragments of pyramidal crystals revealed the variable proportions of the two groups from the top to the base. Near the top, the crystal consists entirely of group C, with 1T as the dominant polytype. Near the base, both groups A and C are present. Back-scattered electron images from cross-sections parallel to the pyramidal axis showed mosaic contrast near the base, suggesting that two compositionally-different domains of several tens of microns in size are present, whereas the contrast was uniform near the top. Electron microprobe chemical analysis indicated the compositions $\left({\text{Fe}}_{2.31}^{2+}{\text{Fe}}_{0.69}^{3+}\right)\left({\text{Si}}_{1.31}{\text{Fe}}_{0.69}^{3+}\right){\text{O}}_5{\left(\text{OH}\right)}_4$ and $\left({\text{Fe}}_{2.16}^{2+}{\text{Fe}}_{0.84}^{3+}\right)\left({\text{Si}}_{1.16}{\text{Fe}}_{0.84}^{3+}\right){\text{O}}_5{\left(\text{OH}\right)}_4$. Electron back-scattered patterns (EBSPs) confirmed that the domain with Si-rich composition belongs to group C and that with Si-poor composition to group A. This is the first evidence that specific chemical compositions are related to the polytypic structures in cronstedtite. Transmission electron microscopy revealed that intergrowth of groups A and C at the monolayer level is also present as stacking disorder in both domains near the base, whereas such intergrowth was not observed in the region near the top.

Experimental illitization of smectite was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Experiments were performed on the <2 µm fraction consisting entirely of smectite separated from a soil formed on subvolcanic rock located in the External Zone of the Betic Cordilleras (southern Spain). Amounts of 0.25 g were added to different solutions: seawater, and three K-enriched seawater solutions prepared by adding KOH to seawater whose final [K] values were 0.1, 0.5 and 1 M, respectively. The experiments were performed at 50°C over a period of 30 days. The XRD patterns showed no mineralogical changes in residues from seawater or from the 0.1 M [K] solution. With increasing pH and K molarity, the smectite peak, initially at 1.4 nm, became broader. This change in the smectite peak was more significant in the residue from the 1 M [K] solution. The appearance of a small shoulder at 1.0 nm in the residue from a 0.5 M [K] solution showed the beginning of illite formation. However, its appearance was clearer in XRD patterns of the residue corresponding to the 1 M [K] solution. The XRD data from air-dried, glycolated, and heated samples from the 1 M [K] solution indicated the presence of smectite, disordered interstratified illite-smectite (I-S) and illite.

The TEM/AEM studies were performed on the residue corresponding to the 1 M [K] experiment. The HRTEM images revealed that smectite and illite occurred as separated packets with a ferroan lizardite, as a by-product of the smectite-to-illite reaction, interstratified and intergrown with illite. Smectite occurs both as ‘rims’ on the illite packet and in its core. The presence of smectite in the core of illite packet indicates that the lateral transition from smectite to illite was incomplete, taking place by direct replacement of smectite layers as a whole through a dissolution-precipitation mechanism. The experimental study shows that smectite may transform in a wide range of geological and artificial environments involving high-pH K-rich solutions.

Selected-area electron diffraction patterns for the [110] zone of MgSiO3 perovskite are consistent with the orthorhombic unit cell obtained by X-ray diffraction (a = 4.775, b = 4.929, c = 6.897 Å). Various areas of a crystal fragment show diffuse streaking along c*, and well-developed satellite reflections that give a 3-fold repeat along [10]*. Another fragment shows doubled cell dimensions when viewed down [30]. The variable occurrence of the satellite reflectioncs and diffuse streaking indicate subtle variations in ordering, chemistry, or both. Images obtained by high-resolution transmission electron microscopy contain perfectly ordered regions, out-of-phase boundaries, and intergrowths of the two orthorhombic forms of perovskite.

Overgrowths of whiskers of hedenbergite (Ca(Fe2+,Mg)Si2O6) on the hydrous pyroxenoid babingtonite (Ca2Fe2+Fe3+[Si5O14(OH)]) have been observed at Arvigo in Switzerland and Kreimbach/Kaulbach in Germany, and we have studied them with transmission electron microscopy in order to understand their structural relationships and formation. The boundaries between babingtonite and hedenbergite are sharply defined, and the two minerals are in direct contact with no additional phases present. The relationships of babingtonite (Bab) and hedenbergite (Hd) were determined as Bab[100]//Hd[112] in the Arvigo specimen and Bab[$\bar 1$00]//Hd[1$\bar 1$2] in the Kreimbach/Kaulbach specimen. Diffraction derived from Bab(031) and Hd(02$\bar 1$) in the Arvigo samples and Bab(031) and Hd(021) in the Kreimbach/Kaulbach samples were observed in identical positions. The reciprocity between the babingtonite and hedenbergite structures is governed by the direction of the SiO4-tetrahedral chains, and the related configuration of octahedra. Thus, hedenbergite is apparently an epitaxial phase grown on a base of {010} plates of babingtonite. The defined orientation relationship is also consistent with that shown in topotaxial intergrowths of other clinopyroxenes and pyroxenoids. The topotaxial intergrowths may result from diffusion-controlled solid-state reactions, whereas rapid whisker growth is characteristic of supersaturated solutions or a vapour medium. The epitaxial growth of hedenbergite whiskers on babingtonite with an abrupt but coherent change of structure at the interface represents an ideal example where the similar chemical compositions of host and guest contribute strongly to the close structural relationship.

Supposed 'merlinoite' crystals from Monte Somma, Vesuvius (Italy) and Fosso Attici, north of Rome (Italy) represent highly twinned coherent intergrowths between merlinoite and phillipsite on a submicroscopic level. The MER (Immm, a ≈ 14.1, b ≈ 14.2, c ≈ 9.9 Å) and PHI (P 21/m, a ≈ 9.9, b ≈ 14.3, c ≈ 8.7 Å, β = 124.8°) frameworks of similar composition are assembled from identical tetrahedral units, though with a different connectivity. Coherent intergrowth and twinning of the two frameworks lead to P42/mnm pseudosymmetry, which is diagnostic of the intergrowth. Under ambient conditions merlinoite has Immm symmetry or I4/mmm if twinned. a low-symmetry model of space group P121/m1 (a ≈ 14.2, b ≈ 14.2, c ≈ 10 Å, β = 90°) allows structure refinement and quantification of the two frameworks.

Upon in situ dehydration to 250°C the evolution of the unit-cell volume of the Monte Somma merlinoite/phillipsite intergrowth displays an intermediate trend between previously studied pure merlinoite from the Khibiny massif (Russia) and Ba-rich phillipsite.

The Monte Somma crystal studied by temperature-dependent single-crystal X-ray diffraction methods also contained a subordinate chabazite inclusion with no coherent structural relationship to the merlinoite/phillipsite framework. Thus, the modification of the chabazite framework on dehydration could also be studied.

Scanning electron microscopy, focused ion beam (FIB), and transmission electron microscopy are combined to study the intergrowth of 90° rotational components and of ramps in coffin-shaped ZSM-5 crystals. The 90° rotational boundaries with local zig-zag features between different intergrowth components are observed in the main part of crystal. Also a new kind of displacement boundary is described. At the displacement boundary there is a shift of the unit cells along the boundary without a change in orientation. Based on lamellae prepared with FIB from different positions of the ramps and crystal, the orientation relationships between ramps and the main part of the crystal are studied and the three-dimensional morphology and growth mechanism of the ramp are illustrated.

Nd:11Fe:Ti alloys prepared by arc melting followed by splat quenching and annealing have been investigated by electron microscopy. The as-cast microstructure evidenced an α-Fe(Ti) → NdFe11Ti → Nd2(Fe,Ti)17 solidification sequence compatible with a cascade of peritectic reactions. The Nd2(Fe,Ti)17 phase was not detected in the microstructure of the splat-quenched materials, but after annealing the ternary compound grains consisted of a mixture of ThMn12-type and Th2Zn17-type structures exhibiting a consistent (020)1:12//(003)2:17 and [100]1:12//[110]2:17, orientation relation, with the invariant plane sitting at (022)1:12//(333)2:17. A series of 3D microdiffraction experiments carried out on grains presenting a random distribution of planar defects has been used to map the reciprocal space of the intergrown phases.