Jurassic limestones occurring in a screen between two ring dykes are shown to have undergone two periods of thermal metamorphism; the first characterized by a high ratio of CO2:H2O and the second by a high ratio of H2O:CO2 in the vapour phase. The first metamorphism produced minerals characteristic of Bowen's decarbonation series. Some of these minerals became unstable in the second metamorphism and (OH, F) bearing minerals were produced. A stage of fracture-controlled replacement veins with mineral assemblages which indicate a varying CO2:H2O ratio in the vapour and a general falling temperature sequence terminate the metamorphic history. Three new minerals, rustumite (Ca3Si2O7.Caterminate (OH)2), dellaite (Ca12Si6O22(OH)4), and kilchoanite (Ca3Si2O7), of which the last has previously been described, are characteristic of the second episode of metamorphism.

A detrital assemblage of magnesian ilmenite, pyrope, chrome-diopside, rutile, and zircon has been traced to outcropping ultrabasic alkaline rocks, hitherto unknown in the Melanesian region. Analyses and descriptions of these ‘kimberlite indicator minerals’ are given. The host rocks comprise alnöite, an alnöite breccia with calcite matrix, and a magnesian ankaratrite, which are described, with chemical analyses. Emphasis is laid on the abundance of ultrabasic inclusions and xenocrysts and the replacements and transformations they have undergone. Malaita Island promises to contribute significantly to the understanding of the relations between alnöite, melilite basalts, and kimberlites.

Two-pyroxene feldspar gneisses and associated ultramafic rocks of the Jotun Kindred in Southern Jotunheimen display mineralogical layering believed to be of original igneous origin. The geological structure of part of the stratiform massif is described, and is shown to provide a basis, hitherto lacking, for systematic study of the mineralogical and chemical variation of the suite.

With progressive increase in grade of contact metamorphism, aluminous hornblendes in some New England basic hornfelses change from a pale blue-green variety with ragged actinolitic habit, to a deeper bluish-green variety, then to a deeply coloured brownish type with granular habit. At all stages the coexisting plagioclase is appreciably calcic. No outer aureole of albite-epidote-actinolite hornfels has been recognized. The higher grade hornblendes are richer in alkalis and titanium, and poorer in octahedrally co-ordinated aluminium than those formed at low grades. Two analysed hornblendes display an unusual excess of calcium, which occupies the Y site, and another has a very high content of ferrous iron and potassium.

The clino-ferrosilite from the lithophysae in an obsidian from Lake Naivasha, Kenya, originally examined by Bowen (1935), has been shown to be substantially pure FeSiO3, with about 5% MnSiO3 in solid solution. It has the same space-group, P21/c, as clino-enstatite and pigeonite. The unit-cell dimensions are a = 9.718 Å, b = 9·088 Å, c = 5·239 Å, β = 108° 27′. These do not conform to the scheme proposed by Brown (1960): reasons are given why this was not unexpected.

Three isograds may be drawn, indicating increasing grades of metamorphism in the northern Adirondack area, based on the development of garnet successively in biotite-quartz-plagioclase paragneiss, metadolerite and metagabbro gneiss, and in syenite and quartz syenite orthogneisses. Changes in the accompanying minerals show that this is an order of increasing temperature. Rocks of similar chemical composition, suitable for the development of garnet, occur in each grade of metamorphism and geologic studies indicate adequate temperature and depth for the development of garnet even where it is not present. The degree of development of garnet in rocks of similar chemical composition, in even as high a grade as the pyroxene-granulite subfacies, is widely variable. All of the data are consistent with an hypothesis that the successive development of a garnetiferous facies for each of the different kinds of gneisses mentioned required special conditions that facilitated the kinetics of the reaction, such as temperature in excess of that for equilibria, in order for the garnet reaction to proceed. The data are not conclusive as to whether certain non-garnetiferous facies of amphibolites are due to the physical conditions (such as high partial pressure of H2O for the prevailing temperature and load pressure) or to non-equilibria.

Special mineral assemblages in calcareous rocks 0–6 ft from the contact of an epidiorite sill are interpreted as the result of polymetamorphism–regional metamorphism superimposed on an earlier thermal metamorphism in which metasomatism, especially migration of potassium, was important.

Amygdales found metamorphosed in the aureole of the volcanic plug at 'S Airde Beinn, northern Mull, may be divided into three classes by their behaviour on metamorphism. The first class, characterized by the original dominant presence of zeolites, forms feldspar readily. It is related to a type, composed to a greater degree or entirely of ferromagnesian minerals, which seems to have formed by the infilling of originally void amygdales during the recrystallisation of the basalts. The second class, originally containing dominant gyrolite, forms first reyerite and then wollastonite on metamorphism, the wollastonite-filled amygdales being enveloped in a rim of aegirine-augite from the earliest stages owing to reaction between the wollastonite and the basalt. The third class originally contained calcite, now represented by the anhydrous calcium silicates larnite, rankinite and wollastonite. These minerals form concentric monomineralic zones decreasing in Ca/Si ratio outwards. Later reaction has led to the replacement of both basalt and calcium silicates by melilite. Thin aegirine-augite rims surround the amygdales.

The compositions of the groundmass and of the plagioclase and sanidine phenocrysts of a series of over- and under-saturated trachytes indicate that plagioclase will precipitate at some stage in the crystallization interval of all calcium-bearing potassic trachytes. Using this data obtained from natural salic liquids, a concept of crystallization within the system CaA2Si2O8-NaAlSiO4-KAlSiO4-SiO2 may be obtained.

Most circumoceanic basalts contain less and most oceanic basalts considerably more than 1·75% of TiO2. The difference of TiO2 averages is large enough to require rejection of the hypothesis that circumoeeanie basalt results from the assimilation of sial by oceanic basalt.

Mineral data from Glen Clova, Angus, suggest that the development of kyanite in graphite-bearing staurolite mica-schists, treated in terms of a Ca-free system, involved decrease of staurolite and a decrease in biotite MgO:FeO ratio. A kyanite isograd may be defined in Glen Clova as the locality where kyanite joins the assemblage staurolite-garnet-biotite-muscovite-plagioclase-quartz-graphite, the biotite having mol. , although the persistence of this identical assemblage over some 600 metres introduces some uncertainty of interpretation. It is suggested that the reaction staurolite+quartz → garnet+kyanite is unlikely to be a common reaction in nature and that its use to subdivide the amphibolite facies is unjustified.

As indicated by Tilley (1925), albite-rich schists and gneisses can inherit their abnormal chemical characteristics from sediments that are proving to be by no means rare. They may be rich in detrital sodic plagioclase or they may contain authigenie analcime. Some sedimentary analcime rocks (‘analcimolites’) carry normative nepheline and so offer potential parent rocks for nepheline-bearing gneisses provided that, in these gneisses, SiO2 ⩾ (4Na2O+6K2O) in molecular proportions. The chemistry and occurrence of soda-rich sediments are reviewed. Some New Zealand occurrences are newly described and hitherto unpublished analyses are presented for porphyroblastic albite schist and felsitic volcanic arenite from Otago, and for analcime-rich sediments from four localities.

The mode of occurrence of uraninite, pitchblende and coffinite at five localities in south-west England is described. Chemical and isotopic analyses of concentrates containing these minerals provide the following 206Pb/238U ages (My.): uraninite, South Crofty, Cornwall, 277 ± 10; uraninite, Geevor, Cornwall, 223 ± 5; pitcbblende-coffinite, King's Wood, Devon, 206 ± 5; pitchblende, Wheal Bray, Cornwall, 165 ± 4; pitchblende, South Terras, Cornwall, 474 ± 2; coffinite, Geevor, Cornwall, c. 45 (chemical analysis only). These results are compatible with geological and mineralogical evidence. Consideration of these and other results indicates that there were at least three periods of uranium mineralization in south-west England, at c. 290 My., c. 225 My., and c. 50 My. Other intermediate ages may also be valid but further work is required to substantiate these.

The major part of the Kap Edvard Holm complex consists of two series of conspicuously banded gabbroic rocks. The primary minerals of both lower and upper layered series show a progressive change in composition, from higher to lower temperature phases, with increasing height in the complex. Minor fluctuations in the differentiation of the two series occur but the division of the layered rocks into the lower and upper series is based on abrupt and major changes in the compositions of the pyroxenes, olivine and plagioclase. This break is correlated with the injection of a large volume of undifferentiated magma which occurred after much of the lower layered series had consolidated, and from which the rocks of the upper layered series were formed. Twelve pyroxenes, five from the lower and seven from the upper layered series have been analysed; the relationships between their optical properties and chemical composition, and between the cell parameters and composition are considered. The crystallization trend of the pyroxenes is compared with that of the Skaergaard calcium-rich pyroxenes; it is suggested that the restricted enrichment in iron shown by the Kap Edvard Holm pyroxenes may be related to the higher water-vapour pressures which prevailed during much of the period of crystallization.

A recent bore-hole through the Shiant Isles picrite established the existence of 45 feet more of the picritic facies, and also the lower margin of the silt, at a point almost vertically below the exposed 35 feet previously investigated. In the light of new field and laboratory information the pieritic facies is briefly re-examined and its origin discussed.

Examination of previous physical methods of estimating the barium-content of these feldspars showed that they are generally unsatisfactory. A new variation diagram is constructed correlating BaO content and values of d132 determined from diffractometer records. It is estimated that the BaO content of these feldspars can normally be determined to about 2–3% by using this diagram.

Some of the problems of the mineralogy of the series are reviewed in the light of the experimental results, in particular the effect of polymorphic changes on the variation diagram. Some experimental evidence of the effect of different structural states upon the value of d132 is obtained, and the limitations imposed upon the method by the existence of such states are discussed.

Phase-equilibrium relations have been determined at 1000 kg/cm2 water pressure for compositions within the system NaAlSi3O8-KalSi3O8-NaAlSiO4-KAlSiO4 in the area adjacent to the temperature minimum. The composition and temperature of the minimum are Ne50Ks19Qz31 and 750° ± 7° C respectively. The compositions of 102 plutonic rocks and 122 extrusive rocks, from Washington's tables, that carry 80% or more of normative Ab + Or + Ne have been plotted; the areas of high density show a marked similarity to the positions of the low-temperature regions of the synthetic system and suggest that many undersaturated rocks are derived by fractional crystallization from a trachytic magma.

Since its discovery by Tilley in 1930, scawtite has been recognized in several locations in regions of metamorphosed siliceous limestones. Scawtite is believed to be the same as CSH(A) and, as such, has been synthesized sporadically many times during runs in the CaO-SiO2-H2O system where slight contamination from CO2 has occurred. Attempts to synthesize scawtite were successfully carried out at low partial pressures of CO2 in an excess of water. The stability of selected scawtite compositions lies between 140 and 300° C, and above saturated steam pressures is not pressure-dependent, at least up to 50 000 psi. The scawtite facies (2) lies between the tobermorite-calcite facies (3) and the xonotlite-calcite facies (1). A hydration series exists from (1) to (2) to (3).

Lyndochite from Tura dukas, 35 miles north of Nanyuki, Kenya, agrees closely with the type material from Canada in its chemical analysis, in the distribution of the rare earths, and in X-ray diffraction data for powder after heat treatment. The mineral is compared and contrasted with aeschynite. Uranium-poor euxenite is intimately associated with lyndochite at the type locality.

Since its discovery over thirty-five years ago, lyndochite has remained unrecorded outside its type locality of Lyndoch Township in Ontario, Canada. Its distinctive chemical composition sets it apart from almost all other Ti-rich metamiet niobates and, despite the many analyses that have been made on rare-earth niobate-tantalates, specimens that could have been regarded as similar to or approximating to lyndochite have rarely been mentioned. Its unusual characteristics include high ThO2 (about 10%) and appreciable rare-earth oxides (about 20%) with a lanthanon assemblage showing a peak concentration of Nd (and Ce), rather than any of the heavy lanthanons. The proportions of TiO2 (about 20%) and (Nb,Ta)2O5 (about 40%) are comparable to those in numerous niobate-tantalates, but are only associated with the percentages of ThO2 and Re2O3 mentioned above in some members of the aesehynite-priorite series. The lyndochite now described is chemically very close indeed to the Canadian lyndochite, and both specimens give closely similar X-ray diffraction patterns (after suitable heat treatment) which are distinct from those of any other metamict mineral.

Chemical analyses together with optical and physical properties are given for ferroan bustamite, rhodonite, spessartine, spessartine-grossular, and tephroite from contact metamorphosed cale-silicate rocks of the Meldon Railway Quarry, Okehampton. The compositions of these minerals are compared to those from the Treburland manganese mine, Cornwall. An analysis is also given of a spessartine from a pyrrhotite-spessartine skarn rock from the nearby Meldon aplite quarry.