Fluorine, chlorine, zinc, niobium, zirconium, yttrium, and rubidium have been deter-mined on fifteen obsidians from Eburru volcano (Kenya Rift Valley), spanning the range from pantel-leritic trachyte to pantellerite. All pairs of elements show positive correlation coefficients, ranging between 0·769 and 0·998, but with most values better than 0·900. In spite of some very high correlations, only two of the twenty-one best-fit lines pass near the origin of the Cartesian coordinates. Linear distributions are found within two separate groups of elements: F, Zr, Rb; and Cl, Nb, Yt. Zn behaves in general as a member of the second group but seems to be subject to an additional variation. When an element from the fluorine group is plotted against one from the chlorine group the resulting pattern is non-linear. Therefore, although the elements in both groups would generally be considered ‘residual’ (partition coefficients between crystals and liquid approaching zero) there are clearly detectable differences in their variation, and hence their behaviour.

Major-element variations in the obsidians are such that a vapour (fluid) phase would be needed to account for any magma evolution. The trace-element patterns are also impossible by closed-system crystal fractionation and suggest that this fluid may have been rich in halogens, with the metallic elements forming preferred ‘complexes’ with either F or Cl. The F-Zr-Rb ‘complex’ also varies quite independently of the important major oxides (e.g. A12O3) in the rocks. In the case of Rb this is but one aspect of a more significant anomaly, in which there is no sign of any influence of alkali feldspar (which partitions Rb) in the variation. This is remarkable because trachytes and rhyolites have normative ab+or > 50 %, and any evolutionary process controlled by crystal ⇋ liquid interactions must be dominated by the melting or crystallization of alkali feldspar. The results on the Eburru obsidians show that if they are an evolutionary series then either, the process was not crystal ⇋ liquid controlled, or that any such process has been overriden (or buffered) by other processes that have superimposed the observed trace-element patterns. In the latter event, the buffering phase may have been a halogen-bearing vapour.

The same considerations must apply to other pantellerite provinces where Rb appears to have behaved as a ‘residual’ element.

Strictly reproducible syntheses of the trimorphs of composition Cu2Cl(OH)3, atacamite, paratacamite, and botallackite, have been developed. In syntheses involving direct precipitation, or reaction of aqueous solutions with solid phases, reliable results are obtained only if the temperature and time of reaction are carefully controlled. Botallackite, the rarest of the naturally occurring trimorphs, is a key intermediate and crystallizes first under most conditions; subsequent recrystallization of this phase to atacamite or paratacamite, or of the latter from the former, depends upon the precise nature of the reaction medium. The crystallization sequence indicates that paratacamite, as has long been suspected, is the thermodynamically stable phase at ambient temperatures. Spertiniite, Cu(OH)2, can be reproducibly synthesized via one route in the non-commutative titration of aqueous copper chloride with aqueous sodium hydroxide solutions.

A detailed study of pyrite in a number of metamorphosed, stratiform, sediment-hosted Pb-Zn deposits has shown the importance of cataclastic deformation, pressure-solution, and grain growth in the deformation and textural development of pyrite. Primary depositional or early diagenetic microstructures are preserved in pyritic ores deformed or metamorphosed at grades up to mid-upper greenschist facies, whereas at higher temperatures only metablastic or annealed pyrite textures are found. Brittle deformation is found at all metamorphic grades and is favoured by coarse grain-sizes. Pressure-solution is a major deformation mechanism in fine-grained pyritic ores in low-grade metamorphic environments. Grain growth and annealing dominate at higher metamorphic temperatures and are likely to have obliterated any evidence of deformation by dislocation processes. Significant macroscopic ductility of fine-grained pyritic ores in low-grade environments may be accounted for by a combination of pressure-solution, grain boundary sliding, and cataclastic flow.

Kerolites from Goles Mountain (Yugoslavia), Wiry (Poland), Madison Co. (North Carolina), and Kremze (Czechoslovakia) are compared with talc and stevensite. Chemical analyses give a composition for kerolite near R3Si4O10(OH)2.nH2O with R mainly Mg and n about 0·8–1·2. Infra-red data and dehydration-rehydration experiments suggest that the additional water is partly surface-held hydrogen-bonded molecular water, lost up to about 300 °C and easily recoverable, and ‘water’ held as surface hydroxyls, lost at temperatures up to about 650 °C and less easily recoverable. The surface area of kerolite from North Carolina by nitrogen absorption measurements is 196 m2/g.

X-ray data show broad basal reflections, a basal spacing (after Lorentz-polarization correction) of about 9·6 Å and a crystallite size of about five structural layers, which is consistent with the large surface area. Two-dimensional hk bands indicate a randomly stacked layer structure with b ≈ 9·14 Å and a crystallite ‘diameter’ of about 150 Å. The basal spacing shows no expansion in water and no thermal contraction up to 500°C. A partial and irregular swelling with ethylene glycol is obtained only after prolonged cxposure (several weeks). In both respects, kerolites differ from stevensite. Kerolites come close to talc in structure and composition but differ in having a highly random layer arrangement, a slightly enlarged basal spacing, which could be due to misfit of layers caused by random stacking, and weaker interlayer bonding.

Kerolite is considered to be a useful varietal name for this talc-like mineral in agreement with the views of D'yakonov and of Maksimovic. It cannot be defined as serpentine + stevensite.

One of the major obstacles to our understanding of the growth of continental crust is that of estimating the balance between extraction rate of continental crust from the mantle and its recycling rate back into the mantle. As a first step it is important to learn more about how and when juvenile crust is preserved in orogens. The most abundant petrotectonic assemblage preserved in orogens (both collisional and accretionary) is the continental arc, whereas oceanic terranes (arcs, crust, mélange, Large Igneous Provinces, etc.) comprise <10%; the remainder comprises older, reworked crust. Most of the juvenile crust in orogens is found in continental arc assemblages. Our studies indicate that most juvenile crust preserved in orogens was produced during the ocean-basin closing stage and not during the collision. However, the duration of ocean-basin closing is not a major control on the fraction of juvenile crust preserved in orogens; regardless of the duration of subduction, the fraction of juvenile crust preserved reaches a maximum of ∼50%. Hafnium and Nd isotopic data indicate that reworking dominates in external orogens during supercontinent breakup, whereas during supercontinent assembly, external orogens change to retreating modes where greater amounts of juvenile crust are produced. The most remarkable feature of εNd (sedimentary rocks and granitoids) and εHf (detrital zircons) distributions through time is how well they agree with each other. The ratio of positive to negative εNd and eHf does not increase during supercontinent assembly (coincident with zircon age peaks), which suggests that supercontinent assembly is not accompanied by enhanced crustal production. Rather, the zircon age peaks probably result from enhanced preservation of juvenile crust. Valleys between zircon age peaks probably reflect recycling of continental crust into the mantle during supercontinent breakup. Hafnium isotopic data from zircons that have mantle sources, Nd isotopic data from detrital sedimentary rocks and granitoids and whole-rock Re depletion ages of mantle xenoliths collectively suggest that ≥70% of the continental crust was extracted from the mantle between 3500 and 2500 Ma.

Chlorine is the most abundant halogen in sedimentary formation waters with concentrations from <100 to >250000 mg/l. Bromine is the second most abundant halogen at <1 mg/l to >6000 mg/l with iodine from <0.1 mg/l to >100 mg/l and fluorine from <0.1 mg/l to 30 mg/l. Chlorine and bromine show a strong systematic covariation suggesting that they are subject to the same controlling mechanisms. Fluorine only shows relatively high concentrations at elevated chlorine and bromine concentrations showing that fluorine, chlorine and bromine are possibly controlled by the same processes. Iodine does not correlate with any of the other halogens indicating that unique processes control iodine.

Key geological parameters that influence chlorine and bromine (and possibly fluorine) concentrations are the presence of salt in a basin, the age of the reservoir unit and the kerogen-type within the main hydrocarbon source rock in a basin. The presence of salt in a basin shows that sea water was evaporated to halite saturation producing connate waters with high concentrations of chlorine and bromine. The presence of salt also leads to high salinity waters through water-salt interaction during burial and diagenesis. Tertiary reservoirs typically have much lower chlorine and bromine concentrations than Mesozoic or Palaeozoic reservoirs. The age of the reservoir unit may simply reflect the different amounts of time available for formation water to interact with salt. The dominance of type II marine kerogen in a basin leads to higher bromine concentrations. This may reflect the dominance of a marine influence in a basin which is more likely to lead to salt deposition than terrestrial depositional environments. Iodine concentrations are independent of all these parameters. Other geological parameters such as depth of burial, temperature, basin forming mechanism and reservoir lithology have no influence upon halogen concentrations.

Key processes that affect halogen concentrations are sea water evaporation and dilution, water—salt interaction and input from organic sources. Chlorine and bromine data lie close to the experimentally-derived sea water evaporation trend showing that sea water evaporation may be an important general control on halogens. Sea water dilution is probably responsible for most low salinity formation water chlorine and bromine concentrations for the same reason. Sea water dilution can occur either by meteoric invasion during burial, or following uplift and erosion, or by diagenetic dehydration reactions. Water can interact with salt in a variety of ways: halite dissolution by congruent processes, halite recrystallization by incongruent processes, sylvite dissolution or recrystallization and halite fluid inclusion rupture. Halite dissolution will lead to high chlorine and relatively low bromine waters because halite contains little bromine. In contrast, halite recrystallization will lead to bromine-enhanced waters because NaBr dissolves preferentially to NaCl. The occurrence of dissolution or recrystallization will depend on the water rock ratio, greater volumes of water will lead to more dissolution and waters with higher Cl/Br ratios. Sylvite is usually rich in bromine so dissolution will lead to bromine-enhanced waters. Primary aqueous inclusions in halite contain high bromine concentrations so that rupture, during deformation or recrystallization, will lead to bromine-enhanced formation water. A combination of these processes are responsible for the very limited range of Cl/Br ratios although congruent halite dissolution must have a limited role due to the absence of waters with high Cl/Br ratios.

Iodine is strongly concentrated in organic materials in the marine environment; oils and organic rich-source rocks have high I/Cl and I/Br ratios relative to sea water or evaporated sea water. All formation waters are enriched in iodine relative to sea water implying that there has been input from organic matter or interaction with oil. However, hydrocarbon source rock type in a basin has no discernible effect upon iodine concentrations.

A new cathodoluminescence-microscope has been developed with a considerably improved detection limit. Time-dependent luminescence intensity changes observed during electron bombardment enabled the recognition of short-lived, long-lived, and brown luminescence colour types in α-quartz.

Short-lived bottle-green or blue luminescence colours with zones of non-luminescing bands are very common in authigenic quartz overgrowths, fracture fillings or idiomorphic vein crystals. Dark brown, short-lived yellow or pink colours are often found in quartz replacing sulphate minerals. Quartz from tectonically active regions commonly exhibits a brown luminescence colour. A red luminescence colour is typical for quartz crystallized close to a volcanic dyke or sill.

The causes of these different and previously poorly understood luminescence colours were investigated using heat treatment, electron bombardment and electrodiffusion. Both natural and induced brown luminescence colours reflect the presence of lattice defects (nonbonding Si-O) due to twinning, mechanical deformation, particle bombardment or extremely rapid growth. The bottle-green and blue linearly polarized luminescence colour, characterized by a plane of polarization parallel to the c-axis, both depend on the presence of interstitial cations. The yellow and red luminescence colours in α-quartz both exhibit a plane of polarization perpendicular to the c-axis and appear to be related to the presence of trace elements in an oxidizing solution and to ferric iron respectively.

One in four of the Cu-filled cation sites in clinoatacamite, the monoclinic polymorph of atacamite and botallackite, is angle- rather than Jahn-Teller-distorted. Experiments show that this site alone is susceptible to substitution by a non-Jahn-Teller distorting cation of suitable radius and charge, such as Zn2+, and also Ni2+, Co2+, Fe2+, Cd2+ and Mg2+. The crystal symmetry changes to rhombohedral when ∼⅓ of the Cu in this site is substituted by e.g. Zn, thus giving paratacamite; the Zn is essential for stability and forms, with larger proportions of Zn, a series to the end-member in which the site is fully occupied by Zn. This end-member, rhombohedral stoichiometric Cu3Zn(OH)6Cl2, has been characterized using natural specimens from Chile and Iran and is named herbertsmithite. The other cations mentioned behave similarly, producing stabilized rhombohedral paratacamites and end-members analogous to herbertsmithite, which if found in nature, as the Ni analogue has been, should be named species. Clinoatacamite, paratacamite and herbertsmithite have rather similar X-ray powder diffraction patterns, but are readily distinguished by infrared spectroscopy.

Zn-stabilized paratacamite forms blue-green crystals of rhombohedral habit, with vitreous lustre, e = 1.828-1.830, o = 1.835, uniaxial negative, weakly pleochroic O > E, density: 3.75 g cm-3, Mohs hardness: 3-3½; space group R, a = 13.654(5), c = 14.041(6) Å, Z = 24, with pronounced Rm substructure; six strongest XRD lines 5.452 (100), 2.895 (20), 2.760 (74), 2.262 (52), 1.817 (18), 1.708 (21).

Herbertsmithite forms dark green crystals of rhombohedral habit, with vitreous lustre, e = 1.817, o = 1.825, uniaxial negative, weakly pleochroic O > E, density: 3.95 g cm-3, Mohs hardness: 3-3½;; space group Rm with no superstructure observed, a = 6.834(1), c = 14.075(2) Å, Z = 3; six strongest XRD lines 5.466 (55), 4.702 (14), 2.764 (100), 2.266 (36), 1.820 (13), 1.709 (18).

Heavy metal-bearing sediment particles enter river systems by discharge of mine or processing waste, tailings dam failures, remobilization of mining-contaminated alluvium and mine drainage. The mineralogy and geochemistry of these particles is dependent upon the original ore mineralogy, and on processes that have occurred in the source areas, during transport and deposition and during postdepositional early diagenesis. This paper reviews the research carried out to date on the sources, mineralogy, chemistry and fate of heavy metal-bearing particles in mining-affected river systems, and identifies six important avenues for further investigation.

Transmission electron microscope samples were prepared of ALH 78045 and ALH 88045, two clay-and phyllosilicate-bearing Antarctic meteorites, using argon ion milling and focused ion beam (FIB) techniques. ALH 78045 contains clay- and phyllosilicate-filled veins that have formed by terrestrial weathering of olivine, orthopyroxene and metal. Very narrow (∼10 nm) intragranular clay-filled veins could be observed in the TEM samples prepared by argon ion milling, whereas differential thinning and lack of precision in the location of the electron-transparent areas hindered the study of wider (5 — 15 μm) phyllosilicate-filled intergranular veins. Using the FIB instrument, electron-transparent slices were cut from specific parts of the wider veins and lifted out for TEM study. Results show that these veins are occluded by cronstedtite, a mixed-valence Fe-rich phyllosilicate. This discovery shows that silicates can be both dissolved and precipitated during terrestrial weathering within the Antarctic ice. ALH 88045 is one of a small number of known CM1 carbonaceous chondrites. This meteorite is largely composed of flattened ellipsoidal aggregates of serpentine-group phyllosilicates. To determine the mineralogy and texture of phyllosilicates within specific aggregates, TEM samples were prepared by trenching into the cut edge of a sample using the FIB instrument. Results show that Mg-rich aggregates are composed of lath-shaped serpentine crystals with a ∼0.73 nm basal spacing, which is typical of the products of low temperature aqueous alteration within asteroidal parent bodies. Results of this work demonstrate that the FIB has enormous potential in a number of areas of Earth and planetary science.

The mechanism by which secondary porosity in sandstone reservoirs is produced is poorly understood. Previous hypotheses to account for the increased dissolution of framework silicates have invoked the introduction of acidic and/or organic-rich fluids capable of complexing metals. In order to evaluate the relative effects of these factors, the rates of K-feldspar dissolution have been measured at 70°C and 95°C, at pH values of 1, 4, and 9, with and without oxalic acid, at a total pressure of 50 MPa, using direct sampling autoclaves. The presence of oxalic acid increased the dissolution rate of Kfeldspar at pH 4 and 9, but decreased the rate at pH 1 at both temperatures. The maximum increase in dissolution rate was observed at pH 4, 95°C by a factor ∼4. In oxalic-free experiments, the rate of dissolution increased an order of magnitude with each unit decrease in pH in the pH regime 1–4. In the presence of oxalic acid, this dependency of dissolution upon pH decreased to approximately an order of magnitude increase with each decrease in pH by 2pH units. The dissolution process was observed to be stoichiometric under all conditions, indicating that the mechanism by which rates are increased was not due to preferential complexation of aluminium, but rather by an increase in the overall solubility of feldspar in the neutral pH region. This regime of increased rate of reaction of feldspar coincides with that expected to be naturally buffered by the introduction of organic acids into a sandstone reservoir system.

This is a review of the elastic behaviour and pressure (P)-induced structural evolution of zeolites and presents a comparative analysis of the deformation mechanisms of the Si/Al-framework and the rearrangement of the extra-framework species in response to applied pressure. The interaction between P-transmitting fluids and zeolites, which can lead to phenomena such as ‘P-induced over-hydration’, is described. The comparative elastic analysis and the high-P structural data of zeolites reported so far allow us to make some generalizations: (1) The range of compressibility among this class of openframework silicates is large, with bulk moduli ranging between 15 and 70 GPa; (2) Microporosity does not necessarily imply high compressibility, as several zeolites are less compressible than other nonzeolitic rock-forming minerals; (3) Compressibilities of zeolites do not seem to be directly related to microporosity, at least if we model microporosity with the ‘framework density’; (4) The flexibility observed in zeolites under hydrostatic compression is mainly governed by tilting of rigid tetrahedra around O atoms that behave as hinges within the framework. Pressure-induced tilting commonly leads to continuous rearrangement of the framework without any phase transition. More rarely, tilting induces displacive phase transitions and isothermal P-induced reconstructive phase transitions (i.e. with change in framework topology), have not been reported in this class of materials; (5) Deformation mechanisms in response to applied pressure are generally dictated by the topological configuration of the framework rather than the Si/Al-distribution or the extra-framework content. The channel content governs the compressibility of the cavities, leading to different unit-cell-volume compressibilities in isotypic structures.

A detailed study of weathered pyrochlore in the laterite above carbonatite at Lueshe, NE Zaire, has been made in order to determine its chemical and textural variations. Pyrochlore in fresh carbonatite at Lueshe is close to an ideal formula of (Ca,Na)2Nb2O6(OH,F) (where a general formula is A2−xB2O6(OH,F)1−y·zH2O. The first and principal change on weathering occurs at the base of the profile and involves the leaching and partial exchange of A cations together with hydration. This change appears common to weathered pyrochlore worldwide. As a result weathered pyrochlore at Lueshe has a large apparent A cation deficiency with A totals between 0.25 and 0.59. The B cations remain stable. Abundant kalipyrochlore is unique to Lueshe and is thought to be related to the abundance of potassium feldspar in the fresh carbonatite, showing that the actual composition of weathered pyrochlore is a characteristic of a particular deposit. Weathered profiles at Lueshe are not simple trends from the least to most leached compositions. Further factors including variation in whole rock mineralogy and chemistry, and cation exchange and uptake are responsible for local concentrations of strontio-, bario- and calcium-rich, sodium-poor pyrochlore in the ore body, as well as rims of ceriopyrochlore on kalipyrochlore. The most important textural relationship in the Lueshe pyrochlore is the intimate intergrowth with crandallite in the most weathered parts of the laterite. Although pyrochlore persists throughout the weathering profile, niobium-beating goethite is thought to represent the final product of pyrochlore breakdown.

The ferromagnesian silicate minerals, such as garnets, pyroxenes, micas, and amphiboles, appear in a variety of geothermometers and geobarometers. Where complete chemical analyses are available and regardless of bulk composition (metamorphosed pelitic or mafic), the aforementioned minerals commonly contain ferric iron. In mineral analyses using the electron microprobe, ferric and ferrous iron are not distinguished, and all the iron is treated as FeO. In ferric Fe-bearing minerals, this treatment results in (1) low analytical sums and (2) excess cations in the mineral formulae. Assuming ideal stoichiometry (ideal formula cations and oxygens) allows direct ferric estimates in garnets and pyroxenes; amphiboles require additional assumptions concerning site occupancies, and, for micas, no acceptable constraint exists for a ferric estimate. Based on ferric iron determinations for some metamorphic ferromagnesian silicates, the proportion of ferric to total iron increases at higher XMg values. The influence of ferric estimates on T and P calculations depends on the model used and on the extent the ferric estimate alters the relative proportions of end-members. Several examples suggest that, in general, if ferric estimates (or determinations) are made, they should be made for all the relevant minerals.

Pelitic rocks in North Wales, ranging in age from late Precambrian to Silurian were sampled. XRD analysis was used to determine the mineralogy and white mica crystallinity of separated < 2 µm fractions. Results show that three stages of metapelite recrystallization can be distinguished. Stage I metapelites are uncleaved or feebly cleaved with crystallinities > 0.43Δ°2θ; the 1Md polytype dominates < 2 µm fractions, occurring as K-and Na-micas. Stage II metapelites show variable cleavage development and crystallinities in the range 0.26-0.43Δ°2θ; 1Md and 2M1 polytypes occur and K- and Na-micas are commonly regularly interstratified. Stage III metapelites are strongly cleaved with crystallinities < 0.26Δ°2θ; the 2M1 polytype is dominant, occurring as K-mica and paragonite. Pelites bearing pyrophyllite, rectorite, and corrensite are found close to plug-like intrusions and were contact altered prior to regional metamorphism. 1M mica is common in deeply buried but relatively undeformed volcaniclastic rocks of the Arfon Group.

Contours of equal crystallinity (isocrysts) are plotted with metabasite zones on a metamorphic map. This shows that stage I metapelites are equivalent to the subpumpellyite zone (≡?laumontite zone). Stage II metapelites are equivalent to the prehnite-pumpellyite facies and stage III metapelites to the clinozoisite and biotite zones of the greenschist facies.

The occurrence and genesis of Ca(OH)2 and Mg(OH)2 deposits associated with hyperalkaline groundwater from partly serpentinized ultramafic rocks in Northern Oman is reported. Two types of Ca(OH)2 deposit are differentiated; crystalline portlandite formed by the evaporation of Ca2+-2OH− spring waters, and a form of amorphous gel, not previously known in nature. The latter is a product of present-day low-temperature serpentinization. Mg(OH)2 (brucite) in both holocrystalline and gel forms is produced by mixing of Mg2+−2H surface waters with a Ca2+-2OH− groundwater in both surface and groundwater environments. These results indicate that significant differences exist between the processes of medium- and low-temperature brucite generation.

The introduction of a fifth amphibole group, the Na-Ca-Mg-Fe-Mn-Li group, defined by 0.50 < B(Mg,Fe2+,Mn2+,Li) < 1.50 and 0.50 ≤ B(Ca,Na) ≤ 1.50 a.f.p.u. (atoms per formula unit), with members whittakerite and ottoliniite, has been required by recent discoveries of B(LiNa) amphiboles. This, and other new discoveries, such as sodicpedrizite (which, here, is changed slightly, but significantly, from the original idealized formula), necessitate amendments to the IMA 1997 definitions of the Mg-Fe-Mn-Li, calcic, sodic-calcic and sodic groups. The discovery of obertiite and the finding of an incompatibility in the IMA 1997 subdivision of the sodic group, requires further amendments within the sodic group. All these changes, which have IMA approval, are summarized.

Scanning Electron Microscopy and Transmission Electron Microscopy show that normal, slightly turbid alkali feldspars from many plutonic rocks contain high concentrations of micropores, from ∼1 µm to a few nm in length, typically 0.1 µm. There may be 109 pores mm−3 and porosities as high as 4.75 vol.% have been observed, although ∼1% is typical. Only ‘pristine’ feldspars, which are dark coloured when seen in the massive rock, such as in larvikite and some rapakivi granites, are almost devoid of pores. Weathering enlarges prexisting pores and exploits sub-regularly spaced edge dislocations which occur in semicoherent microperthites, but the underlying textures which lead to skeletal grains in soils are inherited from the high temperature protolith. Most pores are devoid of solid inclusions, but a variety of solid particles has been found. Although the presence of fluid in pores cannot usually be demonstrated directly, crushing experiments have shown that Ar and halogens reside in fluids. Some pores are ‘negative crystals’, often with re-entrants defined by the {110} Adularia habit, while others have curved surfaces often tapering to thin, cusp-shaped apices. The variable shape of pores accounts for the ability of some pores to retain fluid although the texture is elsewhere micropermeable, as shown by 18O exchange experiments.

Apart from rare, primary pores in pristine feldspar, pore development is accompanied by profound recrystallization of the surrounding microtexture, with partial loss of coherency in cryptoperthites. This leads to marked ‘deuteric coarsening’ forming patch and vein perthite, and replacement of ‘tweed’ orthoclase by twinned microcline. The Ab- and Or-rich phases in patch perthite are made up of discrete subgrains and the cuspate pores often develop at triple-junctions between them. Coarsened lamellar and vein perthites are composed of microporous subgrain textures. These ‘unzipping’ reactions result from fluid-feldspar interactions, at T <450°C in hypersolvus syenites and T < 350°C in a subsolvus granites, and are driven by elastic strain-energy in coherent cryptoperthites and in tweed textures. Further textural change may continue to surface temperatures. In salic igneous rocks there is a general connection between turbidity and the type of mafic mineral present; pristine alkali feldspars occur in salic igneous rocks with a preponderance of anhydrous mafic phases.

Because alkali feldspar is so abundant (and larger, 10 μm pores have previously been described in plagioclase), intracrystal porosity is a non-trivial feature of a large volume of the middle and upper crust. The importance of pores in the following fields is discussed: 39Ar/40Ar dating and ‘thermochronometry’; oxygen exchange; Rb and Sr diffusion; weathering; experimental low-temperature dissolution; development of secondary porosity and diagenetic albitization; leachable sources of metals; nuclear waste isolation; deformation; seismic anisotropy; electrical conductivity. Important questions concern the temperature range of the development of the textures and their stability during burial and transport into the deeper crust.

It is well established by X-ray crystal analysis that the mineral constituent of bone and of the enamel and dentine of teeth is essentially hydroxy-apatite Ca5OH(PO4)3, and that hydroxy-apatite has a structure differing only in small details from that of the well-crystallized mineral fluor-apatite Ca5F(PO4)3. The main difference, and in fact the only fully established one, between the two structures is that the hydroxy-apatite has a slightly larger unit cell than that of the fluor-apatite. The structure of the latter has been determined by Náray-Szabó, and by Mehmel who finally agrees with Náray-Szabó. We have made what is probably a more accurate determination of the structure, using more extensive X-ray data.

Tobermorite minerals vary in some proper lies, notably in whether or not unidimensional lattice shrinkage occurs by about 300 °C to give a 9·3 form; specimens that do this are called normal, and ones that do not, anomalous. Data are compared for thirteen natural tobermorites and the extent to which normal or anomalous character is related to other properties is examined. The most definite correlations found are with chemical composition and morphology. The conditions of formation of normal and anomalous tobermorites are discussed in the light of synthetic evidence.