In the last twenty years quartz has become of considerable importance to the telecommunications industry, one of its most important uses being the control of the frequency of oscillation of high-frequency transmitters. In this country alone the peak war-time demand for oscillator crystals was well over a million a year.

Although quartz is very abundant in the earth's crust it is usually found in the polycrystalline state or as small crystals. Large crystals, reasonably free from twinning and flaws, are relatively rare and most of the supply for piezoelectric purposes comes from Brazil.

Hydrous micas differ from normal micas in that they contain less potassium and more water. In the calculation of structural formulae from their chemical analyses, two methods have been used which rely on the following different assumptions:

1. As these minerals are often fine-grained and may contain adsorbed water, no reliance is placed on the value of H2O+ (water lost above 105° C.) as a measure of structural water. The water content is ignored and the structural formula is calculated on the basis of 20 oxygens plus 4 hydroxyls per structural unit. This method has been used by Hendricks and Ross and by Grim and Bradley.

2. The water which is recorded as H2O+ in the chemical analysis is assumed to represent hydroxyl groups in the aluminosilicate layers of the minerals. Thus, instead of having 20 oxygens and 4 hydroxyl ions per structural unit as in normal micas, formulae are derived which show less than 20 oxygens and more than 4 hydroxyls, the total oxygen plus hydroxyl remaining 24. This method has been used by Brammall, Leech, and Bannister.

A remarkable series of wollastonite-garnet-idocrase veins occurs in the limestone quarries of Lough Anure in the Thorr area of Donegal. This locality lies on the extreme south of the one-inch Geological Survey of Ireland Sheet no. 9, and on the six-inch O.S. Sheet no. 41. S.E. In this area large isolated relics of Dalradian sediments are surrounded by a quartz-diorite which is highly modified at the contacts. This complex is intruded by an alkali-granite. The relict masses may be roof pendants or enclosures, and they are certainly structurally related to one another. It is the purpose of the present paper to describe the mineralization of one particular set of veins in a limestone forming part of one of the masses and exposed in two quarries about 300 yards SW. of the Lough Anure Technical School.

Chamosite is a commonly occurring hydrous ferrous silicate frequently found in close association with chalybite in marine mudstone deposits, the composition of different beds ranging from almost pure chamosite to pure chalybite. In oolitic ironstones chamosite is found both in the ooliths themselves and also in the groundmass. It occurs as a constituent in shales, as a cementing mineral in sandstones, and is occasionally found in lateritic and other deposits. Mineralogically it is usually regarded as a chlorite, or akin to the chlorites, but evidence has been accumulating which tends to show that some varieties may not be chlorites at all, but are probably closely related to the kaolin group of minerals (Brindley, 1949).

In 1926 schultenite from Tsumeb, Otavi, South-West Africa, was described as a new mineral by L. J. Spencer and related to the compound PbHAsO4. The specimen on which the original description was based is still unique in the British Museum collection and was used for the present study. There appears to be no record in the literature that the mineral has been discovered in any other locality

For the X-ray examination rather small fragments (less than 0·1 × 0·05 mm.) were broken from pieces of crystals since all the available crystals were too large and the material has a high absorption to X-rays. Single crystal rotation, oscillation, and Weissenberg photographs in 6-cm. diameter cameras with Cu-Kα radiation as well as Laue photographs (crystal-plate distance 4 cm.) with tungsten radiation were used to derive the unit-cell dimensions and space-group.

The X-ray work described below has been done on crystals of bredigite obtained from two different sources, the natural mineral from Scawt Hill, County Antrim, and the synthetic mineral from spiegeleisen slags. Both types of material have been fully deseribed by Tilley and Vincent (1948). Their analysis shows that the slag mineral is a calcium orthosilicate in which Ca is partly replaced by Mg, Mn, and Ba, the extent of the replacement being represented by the formula (Cal.59Ba0.08Mg0.31Mn0.09)SiO4. Tilley and Vincent conclude that this orthorhombic (pseudo-hexagonal) phase is identical with the high-temperature form α' of pure Ca2SiO4, the existence of which was suggested by Bredig (1943a), and confirmed by TrSmel (1949) using a high-temperature powder camera. Bredig (1943a) also suggests, on the basis of a comparison of X-ray powder patterns, that the crystal structure of α'-Ca2SiO4 is similar to that of β-K2SO4. The present single-crystal work was originally undertaken in order to investigate the structure of α'-Ca2SiO4 more fully.

In 1929 Väiyrynen discovered a chalcopyrite-bearing pyrrhotine deposit at the village of Luikonlahti, 30 km. NW. of the Outokumpu mine. This occurrence is associated with a complex of serpentine, quartzites, phyllites, dolomites, and diopside-tremolite-roeks, together with penetrating granites, aplites, and pegmatites. The rock association thus closely resembles that of the Outokumpu ore-field.

A white soapy mineral which could not easily be identified in the hand-specimen was collected from a vein in the serpentine rock at Kennack Cove, Lizard, in April 1949. From a preliminary optical examination the mineral was thought to be saponite, and therefore of interest to clay mineralogists. Chemical analysis, X-ray, thermal, and optical investigations were carried out at the Building Research Station.

In this paper is described a series of three small pcgmatite dikes and the skarns produced by them in Dalradiau ealc-silicate hornfelses, and after full discussion certain conclusions are deduced as to the mode of origin of these rocks. This suite has not been described previously and lies to the south of Bunbeg quay and to the east of Loughlin island (fig. 1). Tim only published accounts of the area contain but passing reference to some of the features here described. In 1891 Nolan (1) merely noted the existence of 'remarkable beds of garnetiferous limestone withtremolite' near the small village of Bunbeg, whilst Zealley (2) in 1909 briefly referred to these hornfelses.

In the course of a study of the corrosion products formed by seawater sprayed at a temperature of 85° F. on brass and copper sheets, a pale green compound was isolated which proved on chemical analysis to have the composition Cu2(OH)3Cl. The X-ray powder diffraction pattern of the substance was found on visual comparison to differ from that of atacamite, which has the same chemical composition. The atacamite pattern was obtained from a specimen of the mineral from Moonta, on the u peninsula, South Australia, that had been authenticated by both morphological measurement and optical study; identical patterns were obtained from a number of other specimens labelled atacamite. The pattern of the corrosion product proved to be identical, however, with that of two specimens in the Harvard collection labelled paratacamite. These were labelled as from Remolinos, Vallinar, Chile (no. 97523), and from Sierra Gorda, Chile (no. 82883).

The purpose of this account is to review, from the literature, figures for the replacement of silicon by aluminium in biotites, calciferous amphiboles, and clinopyroxenes. Atomic ratios to be quoted have been calculated on a basis of 24(O,OH,F) in biotites, hornblendes, and pyroxenes alike. This facilitates comparison and the higher factor magnifies differences. It may be emphasized, to avoid possible confusion, that in this discussion it is the amount of silicon replaced by aluminium that will be under review. The ratio of tetrahedrally co-ordinated Al to octahedrally co-ordinated A1 will not be considered, although for the sake of completeness, figures for AI in Y groups will be furnished to show total A1 values. Machatschki's group notation is employed. Comparison between biotites, hornblendes, and clinopyroxenes, for present purposes, may best be made between minerals that crystallized under the same pressure-temperature conditions, to reduce variables. Few analyses of specimens of these three minerals, that have crystallized together in the same rock, are available however. One such paragenesis is quoted below. This association occurs as gneiss-like inclusions in calcite, taken from the Tiree marble.

Alamosite was first described by Palachc and Merwin, i who thought it might be isomorphous with wollastolfite. For that reason it has been re-examined, using X-ray methods.

A specimen from the original locality at Alamos, Sonora, Mexico (B.M. 1910,330) was made available through the courtesy of the British Museum (Natural History), and in physical appearance it tallied with the original description. The crystals were aggregates of fibres arranged in bundles which cleaved perfectly perpendicular to the fibre axes. Small tablets could be readily cut out for X-ray analysis. The refractive indices were very high and the dispersion was large. As the axial ratios found by X-ray methods agreed with those given by Palache and Merwin, the latter's chemical analysis and density determination were not repeated.

During a universal stage investigation of the pegmatitic felspars in the Central Australian charnockites, several alkali-felspars were found which, according to the stereograrms published by Emmons (3, pl. 12), should have been near ' anorthoclase' in composition. This identification, based purely on optical properties, was questioned in the first instance because of the absence of other evidence for a soda-rich suite of minerals in these apparently potassic pegmatites. Two felspars which suggested a high soda-content were chemically analysed. Neither proved to be notably high in soda.

The mineral afwillite is one of the hydrated calcium silicates which are found in set cements. It has the empirical formula 3CaO.2SiO2.3H20; a recent determination of the structure by Megaw (in press) has shown that the structural formula is Cas(SiO3OH)2. 2H2O, the hydroxyl groups being linked directly to silicon atoms. When afwillite is heated it loses water. Parry and Wright observed that practically all the water could be driven off by heating for prolonged periods at 300° C., or for shorter periods at higher temperatures. They also found that a further reaction took place on heating to about 1300° C. The present work was undertaken to investigate these changes, and to identify the products formed, using-X-ray powder methods.

The occurrence of a member of the glaucophane group of minerals in Anglesey has been known since 1888, in which year Blake reported the presence of a blue amphibole in a schist exposed in the neighbourhood of the Anglesey Column, west of the Menai Bridge. In the course of his paper Blake made general remarks on the petrography of the schist and on its field relations. He dwelt at some length on the question of the identity of the blue amphibole which is its most notable constituent, describing its columnar habit and pleochroism, and recording an extinction angle of 15° with the axis of elongation (c). By comparison with a description of glaucophane due to Rosenbusch, Blake concluded that the blue amphibole from the Anglesey rock is a normal glaucophane, although it, an extinction angle as recorded by him is considerably in excess of the 4° to 6° mentioned by Rosenbusch.

Early in 1947 an unusual mineral deposit was discovered at Mavuzi in the Tete district of Mozambique. The discovery was made by native boys searching for corundum on behalf of Senhor Mario Canuto de Carvalho, a Goanese prospector who had for some years been associated with primitive gold and corundum operations on the north bank of the Zambesi. The dominant ore-mineral in the new deposit was superficially similar to the pegmatitic samarskite found in small quantities in the mica-mining districts of the Alto Ligonha in eastern Mozambique; and when exposure of the mineral to a photographic plate confirmed that it was radioactive, the identification as samarskite was accepted both by local prospectors and by most of the field geologists who later worked on the deposits. The presence of uranium in the ore was first proven in a chemical analysis by the Southern Rhodesian Geological Survey.

In the course of a petrological examination of some hundreds of specimens from the Tertiary coastal dike swarm of east Greenland, collected at various times by L. R. Wager and W. A. Deer, it was decided to investigate the nature of the residual glassy mesostasis of one of the olivine-tholeiites, in the hope that it might shed some light on the trend of differentiation of the magma responsible for the bulk of the rocks in the swarm. An account of the petrology of the swarm as a whole will be published in due course, but it was thought that a note on the chemical and physical properties of this glassy residuum might be worthy of independent publication, particularly as it provides an interesting comparison with the results of work carried out by Walker (1930, 1935) on the residual glass from one of the Upper Carboniferous tholeiites from central Scotland. The general features of the east Greenland coastal dike swarm have already been described by Wager and Deer (1938) and Wager (1947).

In a previous paper a description of a method was given which had been developed to determine the indicatrix of small crystals, both in orientation and magnitude, making use of the simple one-circle stage goniometer described by Bernal and Carlisle.

As was explained there, when a crystal is viewed in parallel polarized light, between crossed nicols, the two observed extinction directions are the axes of the ellipse determined by the intersection of the indicatrix with a plane through its centre parallel to the plane of the microscope stage.

Although there have been many publications on the fluorescence MX. of minerals in ultra-violet light, very little systematic work has yet been done in utilizing this property for the elucidation of petrological problems, The response of various minerals would seem to be entirely capricious; but the extensive work done on phosphors shows that this depends on the presence of traces of impurities. The spectacular display given by certain minerals has made a strong appeal to amateur collectors.

In 1943 the present writer made use of a fluorescent variety of zircon to assist in the subdivision of the Archaezoic gneisses and igneous rocks of the Mnsgrave Ranges in Central Australia; and after further fieldwork preliminary observations were published in 1947.