X-ray intensity ratios of Si/Al, Si/Fe, and Al/Fe in micron-sized particles of geochemical standards were found to vary linearly with the composition ratio. The same linear relationship was found for samples of the clay minerals kaolinite and illite.

Low albite and maximum microcline were the two feldspars identified in Coal Measures mudrocks. Standard feldspars were then used to spike a mudrock base to construct standard working curves based on X-ray powder diffraction peak areas. Boehmite was added as an internal standard and also to correct for orientation effects. The samples were ignited at 950°C before the addition of the internal standard. This is advantageous for several reasons, but a disadvantage is that albite was found to undergo partial conversion to K-feldspar. The conversion was not total and the original albite content could be determined. This method is an extension of an existing method for quartz and therefore feldspars and quartz can be determined simultaneously.

The oxygen isotopes of albite, quartz, and zeolites from the Hokonui Hills, New Zealand, constrain crystallization temperatures and the type of pore fluids present during diagenesis. A section of altered vitric tuffs in this region contains an extremely sharp reaction boundary between a heulandite-chlorite assemblage containing fresh detrital plagioclase and a laumontite-albite-quartz assemblage. A laumontite vein follows the local joint pattern and forms the reaction boundary, suggesting that laumontitization occurred as a result of fracturing and increased fluid flow during uplift. The albite (δ18O = +15.0)-quartz (δ18O = +19.9 to +20.5) geothermometer constrains the temperature of alteration between 145° and 170°C with a pore water δ18O of +1.8 to +3.5. The tuff was buried to an estimated maximum temperature of about 225°C, indicating that alteration occurred after maximum burial.

Framework oxygen was extracted from zeolites by reaction with ClF3 after the zeolites were thermally dehydrated in a vacuum. Laumontite was dehydrated at 300°C, and stilbite at 150°C. The precision of the method is typically about ±0.45‰. Fractionation curves for dehydrated zeolites are based on a general expression from the literature for feldspars, which depends only on the Si/Al ratio of the mineral. Measured δ18O values for laumontite in the groundmass of the altered tuff were +14.4‰. The laumontite-quartz pair constrains the temperature to between 139° and 162°C, in excellent agreement with the albite-quartz pair, and supporting the petrographic observation of co-crystallizing albite-laumontite.

Oxygen isotope values for fracture-filling laumontite in the vitric tuff, as well as those for groundmass and vein laumontite from other parts of the stratigraphic section, cluster around +14.5, suggesting that laumontite probably crystallized under similar conditions throughout much of the section. Oxygen isotope values for stilbite veins from various parts of the section indicate that this mineral crystallized at lower temperatures than the laumontite, for a given fluid isotopic composition, in agreement with the observed cross-cutting of laumontite by stilbite.

Transformation of montmorillonite was experimentally investigated using a model system of montmorillonite-alanine at 100 MPa and up to 500°C. Sodium-montmorillonite changed to a mixed layer mineral of sodium- and ammoniumn-montmorillonites (Na/NH4-Mnt) in the temperature range from 150 to 400°C. Ammonium ions were the decomposition product of alanine above 150°C. The Na/NH4-Mnt transformed to regularly and randomly interstratified minerals of NH4-montmorillonite and NH4-mica (o. NH4-Mnt/NH4-Mic and d. NH4-Mnt/NH4-Mic) at 400°C. These mixed layered minerals transformed to ammonium-mica at 500°C. Ammonium-analcime appeared and coexisted with the smectites at temperatures over 200°C, and with albite for those over 400°C.

In comparison with the results of previous experiments in which there was no organic component, the present results revealed that (1) some uncommon mineral phases appeared by replacement of sodium ions in montmorillonite with ammonium ions, i.e., NH4-Mic, o. and d. NH4-Mnts, o. and d. NH4-Mnt/NH4-Mics, and (2) ammonium-analcime appeared. The mineral assemblages and alteration sequences correspond better with those observed in the natural system than those known from experimental results in aluminosilicate-water system.

Altered perthites from a weathered pegmatite in the Spruce Pine District, North Carolina, were characterized by electron microprobe as a K-rich microcline host with lesser Na-rich plagioclase having a lamellar morphology. Light-optical and transmission electron microscopy (TEM) show microtextural elements such as phase boundaries, holes and microfractures that could serve as potential nucleation sites for alteration to clay minerals.

The host microcline contains albite and pericline twinning textures that vary in character; the amount of each twinning type and/or the size of twin individuals changes on a μm scale. Plagioclase ranges from large lamellar vein and film albite (visible in the light microscope) to cryptoperthite whose size ranges from μm to perhaps 100 Å. The smallest-scale albite appears to be a late-stage phase of exsolution in which lamellae have nucleated heterogeneously on albite-twin composition planes in the microcline.

Alteration is concentrated in vein and film albite, especially along grain boundaries with microcline. Powder X-ray diffraction (XRD) patterns of intensely altered pegmatite show halloysite. Holes, microfractures, vein albite/host microcline boundaries and microcline/halloysite boundaries trend parallel to the traces of (010) and {110}, suggesting that these directions are pathways along which fluids migrate. Cleavage and microfractures occur along, and holes are bounded by, these directions. Holes are associated with dislocations and the latter are observed at feldspar/clay boundaries. Twin domains and cryptoperthitic albite are less susceptible to alteration than coarse lamellar albite and regions containing negative crystals and microfractures. However, microtextures in some areas containing halloysite suggest that once fluids penetrate the crystal, alteration may proceed preferentially in more strongly twinned regions.

Experimental alteration of albite in deionized-distilled water at 150° to 225°C for various times up to 30 days was performed to elucidate formation processes for alteration products of albite in aqueous solution. The alteration products were examined by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). The surface compositions of albite before and after alteration were investigated by X-ray photoelectron spectroscopy (XPS). TEM clearly showed that an amorphous leached layer was produced on the albite surface at the earliest alteration stage together with small amounts of allophane. The leached layer increased successively in thickness and tended to be detached from the albite surface as alteration proceeded. Noncrystalline fibers less than 0.5 µm in length appeared within the leached layer matrix and transformed into thin flaky smectite and small amounts of K-mica. The leached layer gave electron diffraction patterns with a diffuse halo, whereas the flaky smectite displayed rings at 4.51, 2.61, and 1.54 Å. EDX confirmed that the flaky smectite consisted mainly of Si and Al, and small amounts of Na. The smectite was formed in the stability field of Na-smectite for the system of Na2O-Al2O3-SiO2-H2O.

The objective of the present study was to determine the predominant minerals in sedimentary rocks using Fourier-transform infrared (FTIR) spectroscopy and chemometric analysis. The chemometric analysis was performed on three types of sedimentary rock samples (claystones, clay slates, and sandstones), each with different predominant mineral components. Chemometric models were created to determine the major minerals of the rock samples studied — chlorite, muscovite, albite, and quartz. The FTIR spectra were obtained in transmission mode from pressed pellets of KBr-sample mixtures or by diffuse reflectance from hand-packed mixtures of samples with KBr. Spectral regions measured were 4000-3000 and 1300–400 cm-1, which contained important spectral information for the creation of the chemometric models. Principal component analysis was used in the chemometric method, with calibration models being created by a partial least-squares regression method. The mean relative error, standard error of prediction, and relative standard deviation were calculated for the assessment of accuracy, precision, and reproducibility. The value of the mean relative error was 15–20% for most of the calibration models; the value of the standard error of prediction was up to 6 w/w % for most of the calibration models. The values of the standard relative deviation ranged from ~2 to 8% for calibration models based on diffuse reflectance spectra whereas calibration models based on transmission spectra had values of relative standard deviation of ~15-20%.

Pollucite is a silicate mineral of the rare element caesium, occurring in granitic pegmatites. Experiments have been carried out at 450, 600, and 750°C, 1.5 kbar, to study the equilibrium between pollucite, albite and the co-existing hydrothermal solution. When pollucite co-exists with albite, the alkaline composition of the solution is buffered. The Cs/Na ratio of the solution has been determined to be 0.11 at 450°C 0.22 at 600°C and 0.23 at 750°C. Pollucite contains about 15 mol.% of sodium, whereas albite is almost purely sodic. In nature, pollucite with more than 82 mol.% caesium has never been found. This can be explained by the absence of solutions in granitic pegmatites having a higher Cs/Na ratio than those determined by us.

Experimental breakdown of staurolite + inclusions of albite and muscovite (representing an aluminous Fe-rich metapelitic composition) occurs within the KNFMASH system at 800°C and 0.1 GPa under fluid-present conditions over periods of 2 days to 8 weeks. The overall melt-producing reaction is staurolite + muscovite + plagioclase + vapour = hercynite + corundum + mullite + quartz + liquid, and involves three reactions; staurolite + vapour = hercynite + corundum + quartz + liquid, albite + vapour = mullite + liquid, and muscovite + vapour = mullite + liquid. Melt (glass) compositions are siliceous (77.2–64.5 wt.% SiO2), peraluminous (A/CNK = 1.5–5.5), and have granite-trondjhemite compositions in terms of normative Ab-Ab-Or contents. Textures indicate that quartz formed later than corundum. The corundum + quartz + hercynite assemblage after staurolite is considered to be metastable and only likely to be found in nature where staurolite-bearing rocks have undergone rapid heating and melting followed by quenching.

A borosilicate glass, containing 25 wt. % of simulated high-level radioactive waste has been reacted with water at 350°C and 500 bars for 14 and 48 days using large-volume ‘cold-seal’ high-pressure equipment. Under these conditions the glass crystallizes a suite of mineral phases including: albite, NaAlSi3O8; aegirine, NaFeSi2O6; riebeckite, Na2Fe2(Fe,Mg)3Si8O22(OH)2; zektzerite, LiNaZrSi6O15; barium-strontium molybdate, (Ba,Sr)MoO4; stillwellite, (Nd,Ce,La)BSiO5; willemite, Zn2SiO4; smectite; a lithium-sodium borosilicate hydrate; melilite (åkermanite), Ca2MgSi2O7. A description of the morphology of these phases is given, together with a number of chemical analyses. The implications of the incorporation of waste species in these mineral phases to the disposal of high-level radioactive waste is discussed.

At Alijó-Sanfins there are many granitic aplite and pegmatite veins crosscutting different petrographic facies of the Hercynian granite batholith and also mica-schists. They are tin-bearing granitic rocks. Thirty-four samples of K-feldspar and 34 of albite from these veins and host granites were analysed to establish the distribution of elements and their fractionation trends in the sequence of feldspar crystallization. Rubidium and Cs increase, and Ba, Sr, Ba/K, Sr/K and K/Rb decrease in K-feldspar, whereas Na increases and Sr and Ca decrease in albite, from granites to aplites and pegmatites. In a few aplite-pegmatite veins Rb, Rb/Ba and Rb/Sr increase and Ba, Sr, K/Rb and Ba/Sr decrease in K-feldspar, and Rb increases and Sr decreases in albite from aplite to coexisting pegmatite. Equilibrium was not attained for trace elements between coexisting feldspars.

A two-parameter Margules method has been developed for modelling the thermodynamic mixing properties and hypersolidus phase relations of albite-water (ab-w) melts. The method is based largely on phase-equilibrium and calorimetric data that are either currently available or readily obtainable; P-V-T data are not required.

The new modelling method has been applied to calculate: (1) thermodynamic mixing properties for ab-w melts at 2-5 kbar, 815°C; and (2) hypersolidus phase relations for the ab-w system at 2·5 kbar. Results are uniformly positive—activity-composition relations are similar to those predicted by equations based on P-V-T data, excess enthalpies are in good agreement with data obtained from calorimetry, and calculated phase relations are fully compatible with phase-equilibrium data for ab-w melts acquired at 2·5 kbar.

It is concluded that the Margules method for thermodynamic modelling of ab-w melts is a practical alternative to the P-V-T modelling method.

The North Qôroq centre consists of a number of units of syenite, all undersaturated, with later units in sharp intrusive contact with earlier ones. Chemical and mineralogical characteristics have been determined by primary crystal-silicate liquid equilibria and also later, extensive, metasomatic alteration probably involving an alkali-rich aqueous phase. Cathodoluminescence studies on feldspars, the dominant phase present, reveal the development of red-luminescing albite in all the rocks affected by a late-stage fluid phase in contrast with the blue luminescence shown by unaltered perthites. Spectral and chemical investigation of the feldspars confirms earlier views that red luminescence is caused by Fe3+, an impurity in the feldspar structure, but also indicates that, for red luminescence to be seen, the blue luminescent peak must be greatly reduced or absent. The cause of the blue luminescence is less obvious but may well be related to an oxygen defect centre. Such a centre is apparently absent in red-luminescing albites and hence not formed during growth involving late-stage fluids. The fluids evolved from highly peralkaline, undersaturated magmas and metasomatised less evolved syenites forming feldspathoids, particularly sodalite. Once equilibrium had been attained the fluid behaved principally as a passive phase on its passage through the rocks, aiding the unmixing of the alkali feldspars.