Amino acids have been detected in some meteorites and are readily synthesized in prebiotic experiments. These molecules may have been precursors of oligomers and polymers in the early Earth. These reactions were likely to happen in the protected confined spaces on the porous surface of olivine and in the interlayer nanospace of montmorillonite. This study describes experimental and theoretical research on the sorption of l-alanine onto surfaces of silicate minerals, olivine and montmorillonite. Kinetics of the sorption of this amino acid at different pH media was performed. This sorption has been also studied at atomic scale by means of quantum mechanical calculations finding that this sorption is energetically favourable. These results strongly support the premise that minerals could have actively participated in prebiotic reactions.

Iddingsite rimming olivine in a basanite from the Limberg, Germany, is composed of saponite and goethite. Transmission electron microscopy of ion-thinned, oriented crystals suggests a two-stage alteration process. At first, the olivine breaks into a mosaic of 50-Å diameter {110} bounded needle-shaped domains which change to a metastable hexagonal phase having a = 3.1 Å and c = 4.6 Å, probably of close-packed, metal-oxygen octahedra. This reaction opens solution channels in the olivine which are detectable from about 20-Å diameter and are parallel to the olivine y-axis. Laths of smectite, one or two layers thick, 20 Å wide, and as much as 100 Å long parallel to their y-axis nucleate from the metastable phase and begin to fill in the solution channels. The laths orient with smectite (001) parallel to olivine (100). As the channels widen, prismatic {110} goethite crystals form directly from the metastable hexagonal phase. This first stage thus provides heterogeneous nuclei of smectite and goethite, formed epitactically and perhaps topotactically from a metastable intermediary.

In a second stage,these nuclei enlarge by deposition from solution as water migrates readily through the solution channels. A reduction in total volume allows smectite veins to form, misoriented with respect to the olivine. The reaction conserves iron, requires the addition of aluminum and water, and releases magnesium and silicon. Electron microprobe analyses of the iddingsite indicate that the smectite is saponite.

The formation of iddingsite by the oxidative weathering of Fo80 olivine begins by solution of Mg from planar fissures, 20 Å wide and spaced 200 Å apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for the topotactic growth of goethite. Cleavage cracks < 50 Å in diameter allow Na, Al, and Ca from adjacent minerals, particularly plagioclase, to enter the altering olivine while Mg and Si diffuse away. In the early stages of weathering, strips of Fe-rich smectite (saponite), 20–50 Å wide and 1–7 layers thick, form bridges 50–100 Å long across the planar fissures. Dioctahedral smectite crystallizes on the margins of wider cleavage-controlled fissures; with further weathering halloysite is formed away from the fissure walls. In the ultimate stages of alteration, the saponite and dioctahedral smectite are lost, leaving a porous, oriented aggregate of goethite crystals each measuring about 50 × 100 × 200 Å (X, Y, Z, respectively), with sporadic veins of halloysite crossing the pseudomorph.

A number of chemical reactions (mass-action expressions) have been proposed to describe serpentinization of olivine in terrestrial serpentinites. Some have been applied to interpreting the formation of serpentine-group minerals in CM carbonaceous chondrites. The widely used olivine + pyroxene → serpentine (ol + px → srp) reaction is quantitatively inconsistent with observed ratios of olivine to pyroxene and olivine to serpentine in CM carbonaceous chondrites. The reaction of 5ol → 2srp is most consistent with constraints from textural observations at the scale of individual partial and complete pseudomorphs of serpentine after coarse olivine in CM chondrites, observed co-variations in modal abundances of reactant and product minerals in CM chondrites, and experimental geochemical kinetics. Furthermore, the 5ol → 2srp reaction provides insight into the mobility of solute species in the aqueous alteration environment of CM carbonaceous chondrites.

The lattice parameters and the crystal and magnetic structures of Fe2SiO4 have been determined from 10 K to 1453 K by high-resolution time-of-flight neutron powder diffraction. Fe2SiO4 undergoes two antiferromagnetic phase transformations on cooling from room temperature: the first, at 65.4 K, is to a collinear antiferromagnet with moments on two symmetry-independent Fe ions; the second transition, at ~23 K, is to a structure in which the moments on one of the sets of Fe ions (those on the ‘M1 site’) become canted. The magnetic unit cell is identical to the crystallographic (chemical) unit cell and the space group remains Pbnm throughout. The magnetic structures have been refined and the results found to be in good agreement with previous studies; however, we have determined the spontaneous magnetostrictive strains, which have not been reported previously. In the paramagnetic phase of Fe2SiO4, at temperatures of 70 K and above, we find that the temperature dependence of the linear thermal expansion coefficient of the b axis takes an unusual form. In contrast to the behaviour of the expansion coefficients of the unit-cell volume and of the a and c axes, which show the expected reduction in magnitude below ~300 K, that of the b axis remains almost constant between ~70 K and 1000 K.

The Emeishan large igneous province (ELIP) in SW China is considered to be a typical mantle-plume-derived LIP. The picrites formed at relatively high temperatures in the ELIP, providing one of the important lines of argument for the role of mantle plume. Here we report trace-element data on olivine phenocrysts in the Dali picrites from the ELIP. The olivines are Ni-rich, and characterized by high (>1.4) 100×Mn/Fe value and low (<13) 10 000×Zn/Fe value, indicating a peridotite-dominated source. Since the olivine–melt Ni partition coefficient (KDNiol/melt) will decrease at high temperatures and pressures, the picrites derived from peridotite melting at high pressure, and that crystallized olivines at lower pressure, can generate high concentrations of Ni in olivine phenocrysts, excluding the necessity of a metasomatic pyroxenite contribution. Based on the Al-in-olivine thermometer, olivine crystallization temperature and mantle potential temperature (TP) were calculated at c. 1491°C and c. 1559°C, respectively. Our results are c. 200°C higher than that of the normal asthenospheric mantle, and are consistent with the role of a mantle thermal plume for the ELIP.

X-ray laboratory diffraction contrast tomography (LabDCT) produces three-dimensional (3D) maps of crystallographic orientation. The non-destructive nature of the technique affords the key benefit of full 3D context of these, and other, in situ measurements. This study is the first to apply the technique to any material other than a metal or silicon. We report the first 3D measurements of the crystallographic orientation of olivine, which also makes this study the first to apply LabDCT to (1) a non-metallic, non-cubic system and (2) geological material. First, we scanned fragments of olivine set in resin alongside glass microbeads using LabDCT and absorption contrast tomography (ACT). Then we reconstructed these data assuming an orthorhombic crystal system. We show that: (1) the regions within the sample that index well according to the orthorhombic system correspond to olivine fragments in the ACT image; (2) crystalline regions not corresponding to olivine are not indexed assuming the same lattice parameters; and (3) the diffraction data discriminates crystalline from non-crystalline materials as expected. Finally, we demonstrate that the method resolves sub-degree orientation differences between distinct regions within individual olivine fragments. We conclude that DCT can be applied to the study of rocks and other crystalline materials, and offers advantages over conventional techniques. We also note that LabDCT may offer a solution to the crystallographic measurement of substances that would otherwise be difficult to measure due to challenges in obtaining a perfect sample polish. Future developments to accommodate larger experimental volumes and additional crystallographic systems within a sample promises to expand the applicability and impact of DCT.

This paper describes the ways in which the major rock-forming primary minerals (olivine, pyroxenes, amphiboles, feldspars, micas and chlorites) break down during weathering, the products that develop during this breakdown and the rates at which this breakdown occurs. The perspective chosen to illustrate this vast topic is that of the residual soil weathering profile. Different physical and chemical conditions characterize the various parts of such a profile. Thus, in the slightly weathered rock at the base of the profile, mineral weathering will take place in microfissures and narrow solution channels and the capillary water in such spatially restricted volumes may be expected to be close to equilibrium with the primary mineral. In these circumstances, the weathering product formed may be closely related to the primary mineral both compositionally and structurally. The saprolite higher up in the weathering profile may or may not retain the fabric and structure of the original parent rock, but in either case the close relationship observed between primary mineral and weathering product in the slightly weathered rock may be lost. This part of the profile will usually be affected by freely flowing drainage waters, the composition of which will be far from equilibrium with specific primary minerals. Weathering products which do form are likely to reflect the interaction between bulk water and bulk parent material. In the soil profile, the situation will be further complicated by organic ligands derived from decomposing organic matter or from the direct activities of soil microbes or plant roots. Thus, biological weathering will assume a much greater significance in this part of the profile compared with the mainly inorganic processes dominating in the saprolite and the slightly weathered rock. The general nature of any particular weathering profile will reflect the interactions between climate, topography, parent material, soil biota and time and superimposed upon this complexity, when considering how individual primary minerals break down in detail, will be factors related to the nature of the mineral itself. Particularly important in this respect is the inherent susceptibility of the mineral to weathering, which is related to overall chemical composition and structure, as well as the distribution and density of defects, dislocations and exsolution features, which often control the progress of the weathering reaction.

The paper discusses the mineralogy of eruptives from the Nandewar Volcano, which range in composition from hawaiite and trachyandesite to comendite via tristanite and mafic and peralkaline trachyte. Olivine, Ca-rich pyroxene, and amphibole display marked decreases in 100 Mg/(Mg + Fe) ratios in the sequence trachyandesite to comendite, reflecting variation in host rock compositions. The presence of tscher-makitic subcalcic pyroxene and aluminous bronzite megacrysts in several trachyandesites indicates that these experienced intratelluric crystallization at elevated pressures (6–8 kbar). Some titanomagnetite and plagioclase phenocrysts in trachyandesites may also be moderate pressure cognate precipitates. Groundmass pyroxenes of some trachytes and comendites are strongly acmitic. The presence or absence of coexisting alkali amphiboles and aenigmatite appears to reflect stability over a relatively broad range of fO2 conditions. Aenigmatite rims on titanomagnetite and ilmenite microphenocrysts in several peralkaline eruptives provides support for a ‘no-oxide’ field in T-fO2 space. The Fe-Ti oxide compositional data indicate that magmas spanning the spectrum trachy-andesite-comendite crystallized under conditions of decreasing T and fO2 which broadly coincided with the FMQ synthetic buffer curve. However, a voluminous group of slightly older associated rhyolites appear to have crystallized under significantly more oxidizing conditions.

An olivine grain from peridotite nodule 9206 (Udachnaya kimberlite) was heated in air at 700°C for 9 h. It was investigated by EMPA, by IR and UV spectroscopy and by TEM. The TEM examination reveals hexagon-like inclusions up to several hundred nm in size with a core and rim structure. The AEM data show that the inclusions contain only Mg, Fe and Si as cations. The rims have almost the same composition as the olivine matrix whereas the cores are enriched in iron and depleted in Mg. Electron diffraction data, SAED and CBED, indicate that the rims are composed of a ‘secondary’ olivine while the cores are composed of coexisting feroxyhite FeOOH, bernalite Fe(OH)3 and β-cristobalite SiO2. The presence of nm-sized inclusions in minerals is expected to influence the interpretation of spectroscopic results if spectroscopy is carried out without knowledge of the microstructure.

It is speculated that the complex microstructure of the inclusions is a result of a solid state transformation of a precursor phase, probably a hydrous magnesian silicate, during the experimental heating and oxidation.

The Shiant Isles Main Sill, of Tertiary age, is a classic example of a composite, differentiated alkaline basic sill. The first unit to be intruded was a 2 m thick olivine teschenite which was emplaced with phenocrysts of olivine (mg > 83) [mg ≡ Mg#] and, perhaps, plagioclase. This was intruded by a 24 m thick picrite sill consisting of a mush of melt and suspended olivine phenocrysts (mg > 83) with a D-shaped modal profile. The 140 m thick picrodolerite-crinanite unit was formed by a magma carrying ∼ 10% olivine (mg > 83) as the main phenocryst phase, together with some calcic plagioclase phenocrysts, being emplaced into the top of the picrite unit before the host rock was completely solidified. The olivine phenocrysts settled towards the bottom to form the picrodolerites. In-situ differentiation processes occurred under conditions of almost perfect fractional crystallization, during which very strongly zoned ophitic crystals of olivine (fayalitic rims) and clinopyroxene (hedenbergitic rims), and zoned laths of plagioclase (anorthoclase rims), formed. The last unit consists of ∼ 2 m of granular olivine picrodolerite which was intruded into the upper crinanites, again before the host rock was fully solid.

The mineral zoning patterns are interpreted using published cation diffusion coefficient data, and used to show that the picrite unit might have cooled to the blocking temperatures for Mg and Fe diffusion in < 5 years, and that even the relatively thick crinanite unit cooled very fast, so preserving the zoned Fe-Mg olivine and pyroxene compositions. The compositions of coexisting ilmenites and spinels define a redox trend which initially lies close to fayalite-magnetite-quartz buffer conditions, but later becomes more reducing and approaches magnetite-wustite buffer conditions. The final stages of development occurred during sub-solidus deuteric processes and involved formation of analcime and zeolites, as well as localized sulphide mineralization.

New constraints on the thermodynamic equation of state of water and the predicted water fugacity dependence of OH-solubility at elevated P-T conditions along with its influence on dislocation dynamics in olivine are reviewed. Water is shown to control the style of tectonics of a planetary lithosphere by switching on highly localized weak faulting instead of a broad, slow creeping flow. The transition occurs above a water concentration of 200 ppm H/Si. We argue that this changeover in style of tectonics has important implications for the mechanics of subduction and for plate tectonics in general. Efficient recycling of water is only given if the top strong part of the lithosphere can fail and be dragged down into the mantle in a steady way. Due to different starting conditions and differences in accretion through planetismals, Venus may have never have reached a water content above 200 ppm H/Si in the upper mantle while Mars would have now left the plate tectonic regime due to fast cooling.

The dissolution rates of spheres of two magnesian olivines, two plagioclases, and quartz in tholeiitic basalt have been determined at three super-liquidus temperatures and one-atmosphere pressure. There are considerable differences in the rates among the minerals, e.g. at 1210°, 12° above the liquidus temperature of the basalt, labradorite dissolves at 86 µm/h. and the magnesian olivines at 9 and 14 µm/h. The rates are not time dependent and this, coupled with the existence of concentration gradients in the composition of quenched melt adjacent to partially dissolved crystals, indicates that the dissolution rates are dictated by a combination of diffusion and convection of components to and from the crystal-liquid interface. Values for the activation enthalpy of dissolution are small for quartz and plagioclase (40–50 kcal mol−1) but large for olivine 73–118 kcal mol−1). Dissolution of plagioclase in rock melts seems to be a much more rapid process than crystal growth, whereas olivines apparently dissolve and grow at similar rates. Crystal dissolution is sufficiently slow that ascending, crystal-bearing magma may become superheated and yet fail to dissolve the crystal fraction before quenching; this may be the reason that olivine phenocrysts are often rounded.

Hybrid olivine grains from locally concordant contact zones between bodies of iron-rich ultramafic pegmatite (postcumulate) and layered harzburgite (cumulate) are distinguished from cumulus olivine grains by petrographic features and compositional differences. The hybrid olivines, which in comparison with the cumulus crystals are Fe-Mn-rich and Mg-Ni-poor, represent an arrested stage of replacement and exhibit unusually high NiO/MgO ratios. These features are explained by a disequilibrium process of cation-for-cation exchange between crystals and silicate liquid i.e. magmatic metasomatism. Plots of cations across a contact zone give straight line relationships, a function of the extent to which the metasomatizing liquid infiltrated the cumulate layer. A plot of NiO against MgO enables a distinction to be made between metasomatic olivine and olivine that has fractionally crystallized from a tholeiitic magma. These metasomatic olivines all formed by the replacement of pre-existing cumulus olivine and no chemical evidence has been found to support the formation of olivine in iron-rich ultramafic pegmatite bodies by metasomatism of other phases.