The composition and origin of vanadium-bearing clay minerals in the Jurassic (Morrison and Entrada Formations) sandstones of the Colorado Plateau are reassessed using microanalyses (microprobe and scanning electron microscope). The main V-clays are authigenic illite and chlorite of various petrologic habits: clay casts and matrix, pore lining, replacement of detrital grains. The chemical composition of the V-clays is similar in three different localities in the Morrison Formation separated by about 50 km, suggesting that the V-clays are the result of a large regional event. In both illite and chlorite, Al and V are inversely correlated, showing that V replaces Al in the octahedral position. The chlorite contains a complex mixture of divalent and trivalent cations that cannot fit within a sudoite structure. A classification of V-micas is proposed that employs V3+/sum of the octahedral cations vs. the sum of the interlayer charges. V-illite and roscoelite from the Colorado Plateau are characteristic of diagenetic/hydrothermal environments. For a given locality the composition of the V-clays does not vary with habit, showing that these minerals formed at thermodynamic equilibrium.

Hydrothermal tobelitic phyllosilicates modeled as ISII (R3) ordering with a minimum of 2–3% and a maximum of 6–8% interstratified smectite occur in veins and as replacement of fossils in hydrothermally altered black shale. These heavy metal-rich phyllosilicate veins formed during a Mesozoic-aged, regional-scale hydrothermal event that affected an area which encompasses the Mercur Au district (Wilson and Parry, 1990a, 1990b). Associated minerals include kaolinite, quartz, chlorite, Fe-oxides, I/S (R1, 45% smectite), and pyrite. N and O contents of NH4 phyllosilicates determined by microprobe analysis range from 0.19 to 1.78 and 48.6 to 52.9 elemental wt. %, respectively. Infrared absorption analysis indicates N occurs as NH4+. Very high O analyses are probably caused by contamination with kaolinite. A representative structural formula for the tobelitic material is [(NH4)0.36K0.36Na0.03]-(Al1.91Mg0.13Fe0.03)(Si3.21Al0.79)O10(OH1.88F0.12).

Correlation plots of data from microprobe analyses indicate an atypically high correlation between interlayer charge and octahedral layer charge and no correlation between (K+Na) and N. More typical correlations between N and (K+Na) and between interlayer charge and tetrahedral layer charge are obtained if 2–8% of a beidellitic smectite are factored out of the analyses. This amount of smectite is consistent with modeling of X-ray diffraction data using the computer program NEWMOD (Reynolds, 1985).

Possible sources of NH4 are from introduction by hydrothermal fluids or from thermal degradation of organic matter prevalent within the host rocks during low-grade metamorphism. The occurrence of NH4 phyllosilicate veins in unoxidized shale and the limited occurrence of NH4 phyllosilicates within the host shales suggests a hydrothermal source for the NH4.

Mn-rich graftonite, (Ca,Mn2+)(Fe2+,Mn2+)2(PO4)2, ferrisicklerite, Li1–x(Fe3+,Mn2+)PO4, manganoan apatite, (Ca,Mn2+,Fe2+Mg)(PO4)3Cl, staně kite, Fe3+Mn2+O(PO4) and Mn-rich vivianite, (Fe2+)3(PO4)2·8H2O, occurring in a granitic pegmatite at Soè Valley (central Alps, Italy) were characterized by powder and single-crystal X-ray diffraction (XRD) and electron microprobe analyses. Geochemically, the Mn-rich graftonite phases are poorly evolved Fe/Mn-phosphates of rare-earth elements-lithium (REE-Li) granitic pegmatites. The assemblage Mn-rich graftonite + ferrisicklerite + staněkite has rarely beendocumen ted in pegmatites. Inthe Soè Valley pegmatite, ferrisicklerite forms exsolution lamellae with Mn-rich graftonite associated with manganoan apatite and staněkite. Graftonite is associated with Mn-rich vivianite. Powder and single-crystal XRD data indicate that the unit-cell volume of graftonite increases as a function of Mn2+ content. Staněkite shows a distinctly smaller unit-cell volume with respect to previously reported staněkites, probably due to reduced Mn2+. Vivianite with significant Mn2+ has a unit-cell volume similar to nearly Mn-free vivianite. The formation of Mn-rich graftonite and manganoan apatite is related to destabilization of Mn-rich almandine and biotite during pegmatite formation. Ferrisicklerite forms exsolution lamellae along the 010 cleavage planes of Mn-rich graftonite, whereas staněkite forms by alterationof ferrisicklerite and Mn-rich vivianite due to circulation of late-stage hydrothermal fluids.

Conventional electron-probe microanalysis has an X-ray analytical spatial resolution on the order of 1–4 μm width/depth. Many of the naturally occurring Fe–Si compounds analyzed in this study are smaller than 1 μm in size, requiring the use of lower accelerating potentials and nonstandard X-ray lines for analysis. Problems with the use of low-energy X-ray lines (soft X-rays) of iron for quantitative analyses are discussed and a review is given of the alternative X-ray lines that may be used for iron at or below 5 keV (i.e., accelerating voltage that allows analysis of areas of interest <1 μm). Problems include increased sensitivity to surface effects for soft X-rays, peak shifts (induced by chemical bonding, differential self-absorption, and/or buildup of carbon contamination), uncertainties in the mass attenuation coefficient for X-ray lines near absorption edges, and issues with spectral resolution and count rates from the available Bragg diffractors. In addition to the results from the traditionally used Fe Lα line, alternative approaches, utilizing Fe Lβ, and Fe Ll-η lines, are discussed.

Porous silicon (PS) has been prepared using a microwave-assisted hydrofluoric acid (HF) etching method from a silicon wafer pre-implanted with 5 MeV Cu ions. The use of microbeam proton-induced X-ray emission (micro-PIXE) and microbeam Rutherford backscattering techniques reveals for the first time the capability of these techniques for studying the formation of micropores. The porous structures observed from micro-PIXE imaging results are compared to scanning electron microscope images. It was observed that the implanted copper accumulates in the same location as the pores and that at high implanted dose the pores form large-scale patterns of lines and concentric circles. This is the first work demonstrating the use of microwave-assisted HF etching in the formation of PS.

Quantification of calcium in the cuticle of the fly larva Exeretonevra angustifrons was undertaken at the micron scale using wavelength dispersive X-ray microanalysis, analytical standards, and a full matrix correction. Calcium and phosphorus were found to be present in the exoskeleton in a ratio that indicates amorphous calcium phosphate. This was confirmed through electron diffraction of the calcium-containing tissue. Due to the pragmatic difficulties of measuring light elements, it is not uncommon in the field of entomology to neglect the use of matrix corrections when performing microanalysis of bulk insect specimens. To determine, firstly, whether such a strategy affects the outcome and secondly, which matrix correction is preferable, phi-rho (z) and ZAF matrix corrections were contrasted with each other and without matrix correction. The best estimate of the mineral phase was found to be given by using the phi-rho (z) correction. When no correction was made, the ratio of Ca to P fell outside the range for amorphous calcium phosphate, possibly leading to flawed interpretation of the mineral form when used on its own.

Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate correction for the X-ray continuum (or background) created by the Bremsstrahlung effect from the primary electron beam. This X-ray continuum, as measured on a wavelength-dispersive spectrometer at any particular wavelength, is primarily a function of the mean atomic number of the material being analyzed. One can calibrate the dependence of the continuum on mean atomic number by measuring and curve fitting the X-ray intensities at the analytical peak in pure elements, oxides, and binary compound standards that do not contain any of the analyte or any interfering elements and use that calibration to calculate the X-ray background correction. For unknown samples, the mean atomic number is determined from the elemental concentrations calculated by the ZAF or φ(ρz) matrix correction, and the fit regression coefficients are used iteratively to calculate the actual background correction. Over a large range of mean atomic number we find that the dependence of the continuum intensity on mean atomic number is well described by a second-order polynomial fit. In the case of low-energy X-ray lines (<1 to 2 keV), this fit is significantly improved by correcting the X-ray continuum intensities for absorption. For major and most minor element analyses, the improved mean atomic number background correction procedure presented in this paper is accurate and robust for a wide variety of samples. Empirical mean atomic number background data are presented for a typical 10-element silicate and a 15-element sulfide analytical set up that demonstrate the validity of the technique as well as some potential limitations.

Major and trace element, including REE, analytical data are used as bases for interpreting the petrogenesis of the major igneous components of the northern part of the Ballantrae complex which occurs in the southwestern part of the Midland Valley of Scotland. Most of the peridotite, now serpentinised, is similar to ultramafic rocks in other ophiolite complexes. Mean crystallisation conditions, determined on the basis of co-existing orthopy-roxenes and clinopyroxenes for the dominant peridotite and minor pyroxenite were 1060 (±60)°C—20 (±2) kb and 1240 (±89)°C—25 (±25) kb, respectively. These rocks, of mantle provenance, have compositions consistent with being residues after the extraction of 20–30% of tholeiitic material from the mantle. The presence among them of a rock whose REE contents indicate that it is a plagioclase peridotite, point to the tectonic incorporation of the products of a high level magma chamber.

The mafic parts of the complex have tholeiitic characteristics and developed between 1300° and 1100°C. They do not represent primary mantle melt but fractionated material. Clinopyroxene was the main fractionating phase and more than 10% fractional crystallisation is indicated with increase from gabbros, through beerbachites (metadolerites) of a sheeted dyke complex and pillow lavas, to microgabbros and pyroxene diorites. Biotite diorites and trondhjemites represent the most fractionated products, the latter having affinities with ophiolitic plagiogranites.

The beerbachites of the sheeted dyke complex do not all represent the same stage of fractionation. The pillow lavas have REE patterns similar to rocks found in marginal basins but are markedly different from pillow lavas from the Highland Border Complex in Arran, near the northern margin of the Midland Valley.

Doleritic intrusions known to post-date the obduction of the Ballantrae complex during Arenig times record changing magma provenance during the cooling and serpentinisation of obducted peridotite. There are two groups of dolerites with different petrographical and geochemical characteristics.

The earlier emplaced group, which is subordinate, is characterised by amphibole formed under low metamorphic facies conditions and the virtual absence of Fe–Ti oxides. Chemically these rocks are of primitive tholeiitic character and are similar to modern island-arc basalts. They were derived from a strongly depleted mantle source region. The source region of the later emplaced group, which is predominant, was much less depleted. Clinopyroxene and plagioclase, much of it albitised, are the dominant minerals. Fe–Ti oxides also are common and there are pronounced chilled margins and well-preserved ophitic textures. Although showing mildly alkaline tendencies, these rocks originated from a tholeiitic parental magma of “within-plate” type.

Both groups show evidence of rodingitisation and associated alteration related to serpentinisation of the peridotite. During the metasomatic activity, only some elements were mobile, while Al2O3, total Fe, MgO, TiO2, Cr, Ni, Nb, Y and Zr remained almost constant. Assessment of original magma type and geotectonic environment, and demonstration that both groups of doleritic rocks show the products of fractionation, has relied heavily on data for the apparently immobile elements and on petrographical study which identified those rocks least affected by alteration.

Minimum T and P conditions for the crystallisation of banded amphibole (tschermakitic pargasite)-bearing garnet metapyroxenites that occur beneath and within a tectonically emplaced unit of serpentinite are 900±70°C and 10–11 (possibly 14–15) kb. This indicates both a depth provenance of at least 35–45 km for the obducted oceanic lithosphre which forms part of the ophiolite assemblage of the Ballantrae complex and also a palaeoheat-flow of at least 20°C/km. The metapyroxenites are interpreted as representing the products of subsolidus recrystallisation of a mantle accumulate pyroxenite. Together with associated amphibolites and epidote-rich mylonites formed at higher levels, they constitute a thin, transported and telescoped aureole made up of tectonic pieces of successively-formed metamorphic rocks that welded on to the base of an upward-moving and progressively-cooling peridotite slab.

Estimates of temperature of recrystallisation of the metapyroxenites were obtained using the garnet-pyroxene and garnet-amphibole exchange reactions as geothermometers. Estimates of pressure were obtained from assessments of the stability fields of the amphiboles, clinopyroxenes and garnets present and of the mineral assemblages in relation to published studies on the eclogite-granulite-amphibolite facies system.