Studies are described of various specimens of diamonds made by the General Electric Company of New York, and by Allmänna Svenska Elektriska Aktiebolaget, Västeras, Sweden. The G.E. synthetic diamonds always contain single crystal inclusions of nickel or of a Ni-rich face-centred cubic compound. These are strictly parallel to the diamond surrounding them. If the nickel inclusions are twinned on (111), the diamond is similarly twinned; and this is usually the case. It is suggested that epitaxial growth is part of the mechanism of the graphite-to-diamond transformation in the G.E. technique. Other powdered or single-crystal inclusions are also found; some of those correspond to compounds that occur in meteoritic carbon. There is no parallel growth in such cases. The Swedish synthetic diamonds do not contain nickel, but they are generally less well-crystallized than the G.E. specimens. Both, however, give good diffraction spots indicating a well-ordered structure with (except very rarely) no trace of graphite present.

A new mineral with the approximate composition of Fe2MgTi3O10 and isostructural with pseudobrookite Fe4Ti2O10 has been observed in an olivine-augite-alkali-feldspar rock of the Karroo succession from the Mateke Hills area in south-eastern Southern Rhodesia. Chemical analysis and indexed X-ray powder data (α 9·77, b 9·95, c 3·73 Å.) of the mineral are given, and the name kennedyite is proposed. The name karrooite is proposed for the artificial product MgTi2O5.

Calcite is widespread in amygdales associated with the zeolites; the characteristic forms being and a steep scalenohedron in the zone , usually . Crystals from one locality have faces of , a form new to calcite.

Electron micrographs of scarbroite show thin platy crystals of about 1 μ size, having rhombic outlines with angles 66° ± 1° and 113° ± 1°. Single-crystal electron-diffraction patterns show rectangular net patterns, with d100 = 9·90 Å., d010 = 14·67 Å., γ* = 90° ± 0·05°. Strong hk0 reflections show a pseudohexagonal arrangement, but true symmetry is probably orthorhombic or monoclinic. Faces outlining rhombic forms are of type {11l}, .

An X-ray examination of the type specimen of stokesite gave a 14·41, b 11·61, c 5·23 Å.; space-group Pnna. The unit cell contains 4[CaSnSi3O11H4] and is derived from Hutchinson's morphological unit by the transformation [010/001/100]. X-ray powder data are given.

The parageneses of opaque minerals in three Assynt rocks are described. A biotite-diorite dyke-rock of Lewisian age is characterized by a primary igneous assemblage of Fe-Ti oxides, pyrrhotine, and pentlandite. Effects of metamorphism are recognized, particularly in the oxidation of ilmenite in a Lewisian epidiorite dyke-rock. Cromaltite contains a primary assemblage of oxide minerals together with a later hydrothermal sulphide assemblage. Evidence from the opaque minerals cannot be reconciled with a theory of limestone assimilation. The correlation of the distribution of Co, Ni, and Cu in the rocks with the opaque minerals present is considered.

The crystal structure of the clay mineral dickite (Al2Si2H4O9) has been refined to a greater accuracy than that reported in an earlier analysis. Improved lattiçe parameters are: a 5·15±0·001, b 8·940±0·001, c 14·424 ± 0·002Å., β 96° 44′± 1′. The dickite structure shows several significant distortions from the geometry of the idealized kaolin layer, including deformation and rotation of the silica tetra-hedra. The most striking features of the octahedral layer are the extremely short shared edges of 2·37 Å. Although the analysis was not sufficiently accurate to position the hydrogen atoms with certainty, a model consistent with the infrared absorption spectra is proposed. The stacking sequences of kaolin-layer minerals have been considered with reference to the structural features observed in dickite. There are thirty-six ways of superposing two kaolin layers commensurate with the OH-O bonds found in kaolinite, dickite, and nacrite. The twelve sequences showing the least amount of cation-cation superposition between consecutive kaolin layers can be used to construct two one-layer cells, kaolinite and its mirror image, and twelve two-layer cells, including dickite and nacrite. The distortions of the kaolin layer introduce secondary variations in the interlayer bonding that suggest that dickite and nacrite are the most stable of the kaolin layer structures, since they possess the shortest oxygen-hydroxyl contacts.

Vaterite, the third unstable polymorph of CaCO3, is recognized by optical and X-ray powder techniques as a major constituent in a carbonated calcium silicate hydrogel complex formed from larnite at Ballycraigy, Lame, Northern Ireland. Re-indexed X-ray powder data obtained on synthetic vaterite are provided indicating a hexagonal unit cell with dimensions a = 7·135 Å. and c = 8·524 Å., Z = 6CaCO3. The re-indexing is endorsed by the results of electron diffraction study of synthetic vaterite. Vaterite is shown to correspond to the hypothetical CaCO3 member of the bastnäsite-synchisite mineral series on the basis of extrapolated cell dimensions and optical properties. A structural scheme for vaterite is proposed in which Ca layers replace the CeF layers in bastnäsite, and near-vertical CO3 groups are present. The stability relations of natural vaterite are discussed and comment made on the recent observation of vaterite, in a like environment, in carbonated cements and mortars.

The first scientific examination of the Dalgaranga crater has revealed specimens exhibiting a variety of structures and compositions hitherto unknown in connexion with any meteorite crater. Excavations have yielded much-weathered specimens and permitted measurements of the form and depth of the original pit. The question of age is considered, and the impacting meteorite is thought to have been largely stony but at least in part a mesosiderite.

A number of representative examples of the Lewisian acid pegmatites of South Harris are described, and the presence of the following minerals has been established: quartz, albite, microcline, biotite, muscovite, magnetite, beryl, spessartine, gahnite, eolumbite, monazite, zircon, pyrite, epidote, tourmaline, apatite, thorite, uraninite, thorogummite, uranophane, kasolite, betafite (?), and allanite. Spectrographic, optical, and X-ray powder data are given for some of these minerals, together with chemical analyses of magnetite, biotite, columbite, gahnite, and spessartine. It is believed that gahnite, nranophane, and the pyrochlore mineral (probably betafite) are recorded for the first time from Britain.

This hydrothermal process has been studied using single crystal X-ray methods. A crystal of tobermorite (Ca5Si6O22H10), treated with water at 380° C. and 250 atmospheres, gives a preferred orientation aggregate ofxonotlite (Ca6Si6O17(OH)2), together probably with unoriented silica. The relationship of orientations of product and starting material was established. The change occurs without intermediate dehydration of the tobermorite to the 9·35Å. state. The structural basis of the relationship is discussed, and it is compared with those already reported for the transformations of tobermorite into β-CaSiO3 and of xonotlite into β-CaSiO3. A simple experimental procedure for the single-crystal study of hydrothermal reactions is described.

Chemical data are given for four rocks from the Scourie dyke, Sutherland, and for the constituent minerals. Three of the specimens are unsheared and represent stages in a continuous variation from a one-pyroxene (subcalcic ferroaugite) dolerits through partially amphibolized two-pyroxene dolerite to garnet-plagioclase amphibolite. These changes are not accompanied by conspicuous changes in bulk composition. The garnetiferous varieties represent a border facies of the dyke, which is in contact with little-altered pyroxene-bearing gneisses of the Lewisian complex. The fourth specimen is a hornblende schist formed from the dolerite by shearing. This change also involves little change in bulk composition, and affects impartially the three types of dolerite referred to above. Mineral relations are discussed and a hypothesis advanced to account for the garnetiferous border facies of the intrusion, invoking intrusion while the country rock was at relatively high temperature and pressure.

Helvine and genthelvite are recorded for the first time in Britain; of the former, three occurrences in Cornwall and one in Devon, and of the latter, one occurrence in Cornwall, are described. British danalite has hitherto been represented by two old specimens with the vague locality ‘Redruth’, Cornwall; occurrences at four Cornish localities are described, and a further Cornish locality is provided by two old specimens previously labelled as garnet. Partial chemical analyses for the helvine, genthelvite, and danalite specimens are presented; helvine and genthelvite occur in pyrometasomatic-hydrothermal deposits in metamorphosed calcareous sediments and, in one instance, in greenstone; danalite in hydrothermal deposits or lodes in metamorphosed greenstone; the parageneses of the three minerals are discussed.

A hydrated barium-strontium pyrochlore with only subordinate amounts of Ca and Na has been found in a weathered biotite rock (contact-rock of a carbonatite) from Panda Hill, Tanganyika, as small euhedral yellowish-grey cubic crystals (showing the combination of the octahedron and the cube) in a rock containing euhedral biotite, some orthoclase, and several other minerals. Hydrated Ba-Sr pyrochlore is isotropic, the refractive index varies from 2·07 to 2·10. The reflectivity (vertical illumination) is 13·2 %. H. Poor {111} cleavage. The pyrochlore structure (space-group O7h–Fd3m) and the unit-cell dimensions (a 10·562 Å.) are derived from X-ray powder and Weissenberg photographs. The calculated specific gravity is 4·01 (observed, 4·00 on dried material). Chemical analysis gives BaO 12·5, SrO 6·4, Na2O 0·28, K2O 0·25, CaO 1·35, rare earths (mainly Ce2O3) 2, ThO2 0·6, FeO 0·45, TiO2 3·9, Nb2O5 67·0, Ta2O5 0·22, H2O+ 4·0, other constituents 2·21, total 101·16. After deduction for impurities the following formula resulted: (Ba0·30Sr0·22Ca0·05Ce0·04Na0·03Fe0·02K0·01Th0·01)(Nb1·83Ta0·004Ti0·17)O5·61(H2O)0·80.

The ideal formula for pyrochlore is A2B2O6(F,OH). In the mineral described only a third of the A-positions are occupied by Ba, Sr, etc. Infra-red spectrophotometry does not indicate hydroxyl-groups. When the mineral is treated with TINO3 solution the intensities of the X-ray diffraction lines 333/511, and 444 are changed; hydrated Ba-Sr pyrochlore shows a certain exchange-capacity.

The name pandaite, from Panda Hill, is proposed for the new mineral.

Mapping of the distribution of zeolites in the Antrinl basalku has revealed that gmelinite is confined to a narrow zone along the eastern seaboard of Antrim. This zone comprises less than 1% of the area of the basalts, but in it gmelinite is extremely abundant. The gmelinite zone is superimposed upon the lava pile, and the minerals in it are clearly later than the laves; it is in the form of a dome, elongated north-west and traceable for 18 or 24 miles in this direction, and is found in the basal parts of the lava pile, locally reaching a height of some 500 feet in the pile. The zone may be related in its position and origin to the Island-magee fault zone. Gmelinite frequently forms a parallel overgrowth on chabazite. Superimposed upon the southern part of the gmclinite zone is a zone of late chabazite and heulandite containing, inter alia, parallel overgrowths of late chabazite on simple or twinned gmelinite.

Specimens of delorenzite from the type locality, Craveggia, Val Vigezzo, Piemont, have been examined and found to be close to tanteuxenite from Australia. The X-ray powder patterns are virtually the same, and the chemical analyses (including the relative abundances of the rare earths) are closely similar.

Zambonini's original (1908) specimens have not been re-examined, but are without reasonable doubt the same as the specimens now described; the considerable discrepancies between the old and new analyses can be explained by the difficulty of the separations. It is suggested that the name delorenzite be abandoned despite its priority because of its association with an incorrect analysis.

The single crystal X-ray methods for the study of exsolution phenomena in pyroxenes previously described by the authors have been applied to the pyroxenes of the Skaergaard intrusion. The results for about fifty pyroxene crystals, selected from various levels between the chilled margin and a height of 2600 metres in the layered series, are presented and are correlated with previous optical descriptions. Whilst the correlation between the results of the optical and X-ray examinations is in general satisfactory, the present investigation shows that the X-ray techniques can in some cases extend our knowledge of the Skaergaard pyroxenes.

The top 2 inches of the Lower Magnesian Limestone is feebly but persistently mineralized along its outcrop from Nottingham to Doncaster, predominantly with galena and a little cerussite, frequently with uraniferous asphaltite containing 0·2 to 1% U3O8. Wulfenite, both platy and pyramidal in habit, occurs at Bulwell and Kirkby in Ashfield. The mode of formation and the age of these minerals are discussed.

Calculations are presented, based on modal and chemical analyses of titaniferous iron ore minerals from two localities (Skaergaard and Schmoo Lake). They show that Fe: Ti ratios are constant for granular aggregates of ilmenite and titaniferous magnetite formed at any one stage in the cooling history of the containing rock body. From this and other evidence it is concluded that the aggregates are the result of exsolution from original high-temperature cubic solid solutions. For the Skaergaard rocks, the problem of separately crystallized ilmenite, distinct from the granular aggregates, is also discussed.

A stevensite occurring as an alteration product of pectolite in amygdale-like structures within the Whin Sill is described. Data given for the stevensite include optical properties, stain reactions, chemical analysis, X-ray powder data, and D.T.A. curves. The close similarity between many of the properties of sepielite and stevensite is indicated and D.T.A. is shown to be the most satisfactory method of distinguishing between the two minerals.