The influence of cation size on the misfit between the tetrahedral and the octahedral sheets of serpentine layers, and thus on the curvature of serpentine minerals, has been studied using an experimental approach, based on scanning and high-resolution transmission electron microscopies (SEM and HRTEM, respectively) coupled with analytical electron microscopy (AEM), and a theoretical approach, based on the elastic theory of thin plates and the surface stress concept.

Various Ni3(Si,Ge)2O5(OH)4 serpentine syntheses were prepared, with progressive tetrahedral substitution for Si by the larger Ge ion, the ratio Ge/(Si + Ge) ranging from 0 to 100%. Other parameters (temperature, time duration, water pressure) were fixed. From SEM-HRTEM observations and AEM analyses of all samples, two types of serpentine minerals were characterized: (1) curved structures of tubular or ‘roman-tile’ shape (curvature radius of 10 nm for 0% Ge, increasing with the Ge content), when the Ge tetrahedral content is <25%; (2) perfectly plane structures, with hexagonal or triangular shape (view normal to the layers), for greater Ge contents. These results prove the direct influence of cation size on the crystal curvature.

From a theoretical point of view, a single serpentine layer with a misfit between its tetrahedral and octahedral sheets can be considered as an elastic thin plate subjected to two different surface stresses, σ+ and σ−, on its two faces. The difference σ+ − σ− between these two surface stresses was calculated from the above geometrical misfit, and the curvature of the serpentine layer was related to σ+ − σ−, according to the elastic theory of thin plates. The calculated curvature radii, and the Ge content of transition from curved to plane structures, are in agreement with the above observed values. Curved serpentine crystals may then be considered as a stacking of such elastically curved single serpentine layers.

Analysis of the near-infrared (NIR) spectral bands of phyllosilicates, together with the mid-infrared bands, enables testing and confirmation of band assignments for the structural OH vibrations. Spectral analyses of selected smectites and serpentine-kaolin minerals are presented here. The results of this study indicate that dioctahedral smectites may contain both in-plane and out-of-plane OH-bending vibrations, as suggested by Farmer (1974). In-plane bands occur near 800 ­ 915 cm–1, while the weaker out-of-plane vibrations occur near 600 ­ 700 cm–1 and are enhanced in dioctahedral smectites when the structure is disrupted by substitutions. Analysis of the OH-stretching vibrations and their NIR overtone bands is also presented for both smectites and serpentine-kaolin minerals. These overtones are more straightforward for serpentines than for kaolinite, and a strong overtone associated with the kaolinite OH-stretching band at 3620 cm–1 is found that supports its assignment as an OH-stretching band.

The forest across a sharp boundary between greywacke and serpentinized peridotite is described from a site with seasonal rainfall on Palawan, Philippines. The forest on greywacke was of much larger stature (trees up to 26m) than that on the serpentinized peridotite (trees up to 18m). The tree (>10cm dbh) species richness was the same on both substrata with 38 species in one 0.16ha plot on each side of the boundary. There were many more individuals in the greywacke plot (149) than on the serpentinized peridotite (114). Floristically the plots were very different, with only one tree species, an unidentified Madhuca, occurring on both sides of the boundary. The soil over the greywacke was notably more acid, had lower Mg/Ca quotients, and much lower nickel concentrations than the soil over serpentinized peridotite.