In the past decade, differential thermal analysis has developed into a very useful mineralogical technique. The theoretical background for this method has been treated by Speil, Berkelhamer, Pask, and Da vies (1945) and has been modified by Kerr and Kulp (1948, 1949). The application of the method to the clay minerals has been carried out with considerable success by a number of workers in Europe and America. In particular, Grim and co-workers (1942, 1947, 1948) have produced a number of significant papers dealing with the thermal analysis of clays. The method has been extended to other mineral groups such as the carbonates (Faust, 1949; Beck, 1946; Kerr and Kulp, 1947; Cuthbert and Rowland, 1947; Kulp, Kent, and Kerr, 1950), phosphates (Manly, 1950), sulphates (Kulp and Adler, 1950), quartz (Faust, 1948), and the hydrous iron oxides (Kulp and Trites, 1950).

A fundamental problem arising out of the study of symmetrical point groups can be formulated as follows: Let N points in threedimensional space be connected two and two in every possible way by straight lines: what relations must exist between the lengths of these lines if the points are equivalent members of a symmetrical point group ?

The methods of projection used in crystallography (e.g. the stereographic projection) at once show that the points may be considered to be the images of straight lines or planes. The problem formulated above has therefore a direct application to descriptive crystallography and can in this connexion be stated as follows:

A complex of N planes is determined by the points of intersection of the normals with the surface of a unit sphere, i.e. by their poles. What now must the angular relations between the planes be if all are equivalent, that is to say, belong to one and the same simple form ?

In any monoclinic crystal, the zone–axis [uvw] is perpendicular to the plane (hkl) if u/(hc2–lac cos β) = v/(kc2a2sin2β) = w/(la2–hac cos β). In particular, the normal to the face (100) is quasi–parallel to the zoneaxis [r01̄] if c/(a cosβ) approximates to a rational number r.

Epidote has a:b:c = 1•5807:1:1•8057,β 115° 24', and is often twinned on a(100). G. Friedel describes and explains these twins in terms of a pseudo–normal zone–axis [301], with an obliquity of 3° and a twinindex 3. But the choice of a pseudo–normal zone–axis is necessarily arbitrary, since it is always possible to find a rational zone–axis making an angle with any given face–normal less than any assigned angle δ: though the indices of such an axis may involve large numbers.

In 1938 large crystals of almandine garnet were collected by the writer from a cutting excavated during road-widening operations, on the main Huntly—Keith road, near Cairnie church, about 4½ miles from Huntly. In view of their exceptional size and excellent crystal form, it is felt that the occurrence is worth recording. Garnet crystals of comparable size have been recorded by Heddle from several localities. The Cairnie crystals, considering their size and excellent form, must rank with the finest recorded from Scotland.

The rocks at this cutting are coarsely banded garnet-biotite-sillimanite-gneisses with abundant quartz, oligoclase, orthoclase, and biotite, subordinate muscovite, and accessory magnetite, apatite, and zircon. Sillimanite is sporadic in occurrence, forming elongated colourless prisms up to 2 mm. across. The biotite-rich bands generally contain only small garnets, if any, but garnet is very abundant in bands rich in quartz and felspars, and often forms a large part of the rock.

This paper deals with a series of soil-clay minerals which have a widespread distribution in the north-east of Scotland. The original member is a biotite-like mica which breaks down readily in the soil into (i) a vermiculite or (ii) a montmorillonite, depending on the soil-forming conditions operating. Apart from this 'clay biotite' and its decomposition products, the main crystalline constituents of the Scottish soil-clays are a member of the kaolinite group and illite (' clay muscovite'). Iron and aluminium oxides are present in all the clays in the amorphous condition, but crystalline varieties are scarce. The distribution of the minerals and their relationship to the various soft-forming factors will form the subject of a separate communication; here, the nature of the clay minerals and their interrelationships are considered.

Henry How, professor of chemistry and natural history in the University of King's College, Windsor, Nova Scotia, described in 1861 the occurrence of a new calcium sodium borate, which he named cryptomorphite from the microscopic size of the crystals. The mineral was found in narrow seams of mirabilite (glauber-salt) at the junction of anhydrite and gypsum in Clinton quarry, Windsor, where he had also discovered ulexite in 1857. The cryptomorphite occurred as inclusions about the size of a small bean, between the gypsum and crystals of mirabilite.

Les chlorites peuvent être définis d'après G. Tschermak (I), puis t A. Lacroix (2), comme des silicates hydratés d' Al, de Mg, et de Fe, de couleur généralement verte, possédant un elivage facile suivant (001), les lames de clivages étant flexibles, sans être élastiques, comme celles du mica. Dans un travail antérieur, l'un de nous (3) avait tenté d'établir une classification de ces minéraux, en se basant directement sat les données de l'analyse chimique, sans faire intervenir d'idée théorique sur leur constitution, comme l'avait fait G. Tschermak et d'autres auteurs aprés lui. Peu de temps après, un certain nombre de recherches, effectuées à l'aide de rayons X, ont permis d'élucider les caractéres essentiels de la structure de ces phyllites. On peut done raisonnablement en tenter une nouvelle classification chimique tenant compte du schéma structural établi actuellement. C'cst ce que nous nous proposons de faire dans ce mémoire, aprés avoir exposé quelques remarques sur des travaux récents.

Tobermorite, a hydrated silicate of calcium, was described by M. F. Heddle in 1880 from three Scottish localities: two near Tobermory in the island of Mull, and the third a quarry near the pier at Dunvegan in Skye. Further localities for the mineral are Sgfirr nam Boc, Loch Eynort in Skye, and Ardtornish Bay in Morven (Morvern), Argyllshire.

Because of marked similarity in chemical composition it has been suggested that tobermorite might be identical with gyrolite. In view of this and of the current interest in hydrated calcium silicates in cement chemistry the species has been re-examined.

Paralaurionite from a new locality, the Mammoth mine, Arizona, is described. X-ray study and chemical analysis confirm the original characteristics of the mineral as described in 1899 by G. F. Herbert Smith. Measurements are given which establish new forms on crystals from Arizona and also on crystals from a South American locality. A complete angle table for twenty-eight forms is presented.

In the course of the routine X-ray examination of a number of lowgrade iron ores in order to determine their constitution, it was observed that the calcite phase had varying interplanar spacings. Since these variations could have been due to differing solid-solution contents of other carbonates, further consideration was given to this point. The existence of these generally small amounts of solid solution is of some technological interest.

A sample of 'specpure' calcite, supplied by Messrs. Johnson, Matthey & Co. Ltd., was used to provide accurate lattice parameters and interplanar spacings for pure calcite.

In his long conduct of the Mineralogical Magazine and Mineralogical Abstracts our Editor has always shown a ready interest and understanding for each new phase of mineralogy as it has appeared, and thus a contribution to any part of the wider realm of mineralogy would fall in the range of Dr. Spencer's comprehending appraisal. At the same time Dr. Spencer's own published work in mineralogy and the style of his abstracts of the works of others show that his personal interests incline to the classical natural history aspect of mineralogy, which gives first importance to exact observations that establish the individuality of new species, improve and extend the knowledge of well-defined species, or disprove the existence of supposed new minerals.

Nacrite is the rarest member of the kaolin group of minerals. The name was first applied by Brongniart in 1807 to a mineral (talc granuleux of Haüy, 1801) the properties of which were not then adequately described. In 1832 Breithaupt recorded a mineral from an ore vein near Freiberg in Saxony, which has since been called nacrite. In the past, however, 'nacrite' has been applied quite frequently to different nacreous and micaceous minerals, not necessarily of kaolin composition, and the authenticity of the species was not definitely established until 1931 when Ross and Kerr, on the basis of an X-ray study of nacrite from the locality Brand near Freiberg in Saxony, proved the mineral to be a distinct species of the kaolin group.

The peninsula in which the mainland of Shetland ends north of Ronas Voe and Colla Firth is occupied mainly by the Ronas Hill Granite. This body is intrusive into a metamorphic series consisting of orthogneiss on the north and paragneiss oil the north-east, east, and south-east of tile peninsula. It is a biotite-granophyre within which earlier bodies of basic rock varying from diorite to gabbro are found. It is unsheared and unfoliated and is cut by a swarm of dikes with north-south trend which extends from tile north coast to Ronas Voe. There is evidence also of the existence of dikes earlier than the granite. The later dikes comprise spessartine, microdiorite, porphyrite, quartzfelspar- porphyry, and a great variety of felsites which are generally granophyric and spherulitic. Many of the felsites contain riebeckite and aegirine and have a corresponding blue or blue-green colour. From observation of chilling of dike against dike and intersection of dike by dike it has been found that tile basic dikes, spessartine, microdiorite, and porphyrite, are the oldest of the suite, the quartz-felspar-porphyries are older than the felsites, and the blue riebeckite-felsites are younger than white, pink, and dull red felsites which contain neither aegirine nor riebeckite

In the summer of 1951 Mr. R. J. King of Leicester collected from the shatter zone of the main fault in Sheet Hedges Wood quarry, Groby, Leicestershire, specimens of slickensided syenite with quartz veins which contained a creamy white, soapy or powdery material in small cavities in the quartz and on surfaces of movement. The mineral was found from X-ray powder photographs to be the rare clay mineral nacrite. Subsequent searching by Mr. King this year has failed to produce more than a very few grams, mostly on one specimen. The mineral seems to be confined to the region of the main fault and has not been seen in any other part of the quarry.

In vielen Lehrbüchern der Erzlagerstättenkunde und Mineralogie werden die eigentümlichen Vorkommen von Fe-führendem gediegen Nickel als Musterbeispiele orthomagmatischer Differentiate ange-sprochen. Daß das bisher, soweit mir bekannt, unwidersprochen geschah, hat verschiedene Gründe:

1) paßt die Durchschnittszusammensetzung Ni66 Fe33 bis Ni75 Fe25 leidlich gut mit der Lage des Schmelzpunktsminimums im binären system Ni—Fe

2) stammen die wenigen in situ gefundenen und die recht zahlreichen aus Flußseifen ausgewaschenen Stücke eindeutig aus Serpentinen oder Peridotiten, wodurch ein Vergleich mit den Vorkommen gediegenen Platins in Dunit oder Chromitit nahelag

3) hat das chemisch immerhin unedel Verhalten des Ni und natürlich erst recht, des Fe einen Zweifel an der so etwas als deus ex machina wirkenden ‘orthomagmatischen’ Natur garnicht aufkommen lassen und

4) schließlich war das Material in allen Sammlungen so spärlich und wert voll, daß man sich nicht recht an eine ohne größeren Material­verbrauch nun einmal nicht mögliche Untersuchung getraute und so auch die Zahl der Analysen klein und in der Auswahl des Stoffes — zufälligerweise — unglücklich war. Es wird im Folgenden erkennhar sein, wie wenig stichhaltig die Gründe 1-3 sind und daß jede et was umfassendere Untersuchung sofort ‘magmatische Ausscheidung’ oder gar ‘liquides Entmischungsegregat’ ausgeschlossen hätte.