Cliftonite was described by Sir Lazarus Fletcher in 1887 as ‘a cubic form of graphitic carbon’. He put forward reasons for regarding it as a new allotropic modification of carbon and other reasons suggesting that it is a pseudomorph of graphite after some cubic mineral, perhaps diamond, but did not definitely favour either view. On the evidence available hitherto, both suggestions were clearly possible.

Bavenite was first described from Baveno by Artini in 1901 as monoclinic crystals of prismatic habit in pegmatitic druses in granite and given the formula 3CaO.Al2O3.6SiO2.H2O. More recently, the mineral has been described pseudomorphous after beryl from Himalaya mine, Mesa Grande, San Diego County, California, by Schaller and Fairchild (1932) and shown to contain beryllium as an essential constituent. In 1933 X-ray determinations by Ksanda and Merwin indicated a unit cell with dimensions a 9·67, b 11·53, c 4·95Å, and showed the symmetry to be orthorhombic and referable to the space-group V1, Vh1, or C2v1. Revised crystallographic orientation and optical constants were also suggested by these authors.

The material about to be described is from two localities in Switzerland. Of fourteen specimens from a fissure in the rocks below the Muotta Nera, Piz del Laiblau, Val Nalps, Tavetschthal, Graubünden, selected by Mr. F. N. Ashcroft in 1935 and 1936 from a fairly large series stocked by Adolf Caveng of Sedrun, one (B.M. 1937,598) carries the mineral as roughly radiating aggregates of platy fibres of very pale brown colour in bulk.

At Brockhill in Worcestershire, some 11 miles west of Droitwieh, in the valley of the river Teme, a small dike of igneous rock is intruded into the red marls and sandstones of the Downtonian Series.

The dike was figured and described by Phillips in 1848. On the Old Series one-inch Sheet 55 N.E. it was indicated as having a very limited outcrop on the eastern side of the river Teme; but a report of an excursion to Brockhill in 1874 records the presence of igneous rock on the opposite bank. The intrusion was examined during the resurvey on the six-inch scale of the New Series one-inch map, Sheet 182 (Droitwich), and is of interest both on account of its petrographic character and its remoteness from other igneous rocks. It has recently been traced by magnetic methods for a distance of over three-quarters of a mile.

As is well known, quartz rarely shows well-defined cleavages. Kenngott has shown that quartz that has suddenly been cooled, after strong heating, has a tendency to break up in the directions of rhombohedron faces. Breithaupt (cf. Hintze, Min., 1904, vol. 1, p. 1273) mentions ‘cleavage following the primary rhombohedron and the prism, rarely well defined, often passing into conchoidal fracture’.

It may be useful to put on record an example of clear rock-crystal in which cleavage is developed in all three 60° directions of the prism faces. The specimen was originally in the Daimeries collection, in Brussels, having been bought years ago at Idar, near Oberstein on the Nahe, by A. Daimeries. I obtained it from Mr. A. G. F. Gregory, who had bought the Daimeries collection. The locality from which it came is, unfortunately, unknown.

Early this year Mr. Arthur Russell brought me a small specimen of ore from Mill Close mine, Wensley, Derbyshire, for identification. An X-ray powder photograph p1. xxviii, fig. 3, showed that the mineral has the pyrite structure with unit-cell edge a 5.49 Å., and a chemical analysis of a small sample of specific gravity 4·82, yielded Ni 16·69, Fe 29·30, S 53.40% (see table 1). These data identified the specimen as bravoite, a rare mineral new to the British Isles. At a later date Professor W. G. Fearnsides interested himself in our preliminary work and kindly provided me with further specimens of bravoite and accessory minerals from the Mill Close mine. These also have been investigated.

The author arrived at Huckitta station, 135 miles north-east of Alice Springs, towards the end of June, 1937, on an expedition to the Tarlton Range at the north end of the Simpson Desert. The manager of the station, Mr. W. Madrill, said that a haft-caste named Mick Laughton employed on the station had a stone he would like to show, and this was produced by Laughton in the usual diffident manner of the half-caste. It proved to be a flat, rusty mass weighing a little over nine pounds. A few knocks with a hammer soon showed it to consist in part at least of malleable iron, and a meteorite was at once suggested. The specimen was not very closely examined, and the olivines, which show up so excellently on the polished surfaces, were entirely overlooked, which is quite easily done in the case of the iron-shale or the more weathered natural surface of the meteorite, although olivine makes up more than half the volume. It was said that the specimen came off a big stone which stood several feet out of the ground.

In most mineralogical text-books the nepheline-syenite area of Alnö, on the east coast of Sweden, is given as one of the few localities of the rare mineral baddelyite, ZrO2. This information is based on a communication by E. Hussak, who claimed to have discovered the mineral in jacupirangitic varieties of the Alnö nepheline-syenites.

The present writer, being engaged with a petrological and mineralogical revision of the Alnö occurrence, earlier described by A. G. Högbom in his classic memoir of 1895, has in vain looked for the presence of baddelyite. Hussak claimed to have isolated by means of Klein's solution 0·38 gram of pure baddelyite from 100 grams of rock, as well as to have obtained characteristic ZrO2 crystals inn borax bead test. Repeated isolation tests with Clerici's solution on samples from various localities within the Alnö area, however, furnished nothing but residues of melanitic garnet.

In carrying out a petrological examination of pebbles collected by Mr. F. Gossling from the Lower Greensand of Surrey and west Kent, the writer has found a low-power dissecting binocular microscope an extremeIy useful piece of apparatus. The instrument, by Watson, is fitted with two pairs of objectives on a rotating nosepiece, and with two pairs of eyepieces, so that it commands the choice of four different magnifications.

The pebbles are treated in a uniform manner. After the preliminary examination of a ‘bag’ of pebbles, those selected for study are ground flat on one side, finishing on the fine carborundum plate as if for section making. Each one is then mounted on the usual 3 by 1 inch glass slide, taking care not to over-cook the balsam. If the pebbles are treated systematically in batches of six, a dozen pebbles can be mounted in less than an hour, so that the gain of time over section-making is very considerable.

In 1913 the late Mr. J. J. Beringer suggested that it would be of interest to determine the solubility of crushed felspar (a) in distilled water free of carbon dioxide, and (b) in distilled water saturated with carbon dioxide. For this purpose crushed felspar (orthoclase) was covered with water in a silica basin (i) in a desiccator containing potassium hydroxide solution, and (ii) in a desiccator connected with a carbondioxide Kipp's apparatus. These were allowed to stand for a fortnight and the alkalinity of the water Was then determined by N/100 hydrochloric acid. This experiment was continued until the end of July, 1914. A definite solubility was determined in each case and the solubility in the carbon dioxide water was only slightly more than in the water free from carbon dioxide. Unfortunately Mr. Beringer died early in 1915, and the records of his experiment could not be found.

According to their atomic arrangement the minerals found in clays can be divided into the two-layer and the three-layer structures. The members of the first group have alternating silica and alumina layers, e.g. kaolinite; the members of the second group have one alumina (or magnesium or iron) layer between two silica layers, e.g. pyrophyllite. The clay minerals can also be classified into two groups according to their power to diffract X-rays. The first group gives good powder photographs with twenty to forty well-developed lines if copper or iron radiations are used, whereas the second group gives poor diagrams with only a few lines, usually under fifteen, some of which are wide and indistinct. Exposure times for the second group are about two to three times as large as those for the first group. The poor diffracting power for X-rays may be due either to a lack of regularity (‘roughness’) of the lattice, or to an extremely small size of the single crystallites. It is possible that both effects are aetive to some extent, but the lack of regularity of the lattice is probably the main reason. Neither the microscopic evidence nor sedimentation data based on Stokes's law show these minerals to have particles smaller than 10-6 cm., though it is possible that the optical effects such as double refraction are due to aggregation, and it is clear that the equivalent radius is an unsatisfactory measure for plate~shaped particles. Both classifications are shown on p. 141.

It is just over a hundred years since Charles Darwin, during his great voyage, visited Sydney, New South Wales. While there, he was given, by the explorer Major Sir Thomas Mitchell, a small and curiously shaped glassy object. In his ‘Geological Observations’ (1844) Darwin figured this object and speculated as to its origin, which he suggested was volcanic. This is the first recorded reference to what are now known as australites, many tens of thousands of which have been collected from widespread localities over the whole of southern Australia.

In recent years several occurrences of clinoenstatite and of clinohypersthene have been recorded, the identification depending on the oblique extinctions measured from a prominent cleavage. This is, of course, quite inconclusive, because many sections of hypersthene show extinction-directions oblique to the trace of a prominent cleavage, and much fuller data would be necessary before most of these occurrences could be accepted as monoclinic Mg-Fe-pyroxenes.

Sartorite is one of four minerals once thought to be isomorphous. Of these only two are truly so—chalcostibite, copper antimony sulphide, CuSbS2; and emplectite, copper bismuth sulphide, CuBiS2—both orthorhombic minerals. The third, zinckenite, has been shown by two of the authors to be hexagonal and to approach more closely the formula Pb6Sb14S27 ═ 6PbS.7Sb2S3 than PbSb2S4 ═ PbS.Sb2S3. It seemed appropriate to continue a study of the series by an X-ray investigation of sartorite, a lead arsenic sulphide formerly supposed isomorphous with zinckenite. More than usual interest was attached to such a task, since discrepant interpretations of the symmetry and setting of sartorite had been obtained by well-known crystallographers.

Indeed, the difficulties of indexing different crystals of sartorite on the same lattice proved insuperable to G. F. H. Smith and R. H. Solly, so that they devised three incongruent lattices—one monoclinie and two anorthic. Also they used slightly different elements for each crystal. Their device, however, was not uniformly successful with certain crystals of sartorite previously measured by C. O. Trechmann. Two crystals in particular eluded their efforts. These, they decided, could not belong to the same species, but must be another mineral, perhaps a dimorphous form of sartorite, which they then named sartorite-α.

A very interesting kornerupine-bearing rock was sent by Mr. W. H. Cross during 1938 to the Geological Survey for identification. The material, of which about 800 grams were available for study, was stated to have been found in the Port Shepstone district. The occurrence has, however, not been visited by the writer.

The hand-specimens examined were all somewhat weathered. Macroscopically these consisted of an intergrowth of grey, columnar crystals of kornerupine, up to 5 centimetres in length, and adhering iron-stained quartz. Shiny ‘books’ of biotite occur both in the kornerupine and the quartz, while small patches and specks of dark brown tourmaline and bluish grandidierite were observed enclosed in the kornerupine.

The structure of sanidine was described by Taylor in 1933, and Taylor, Darbyshire, and Strunz in 1934 extended the investigation to include the potassium-barium-felspars and albite, and presented a small amount of experimental data for potash-soda perthitic felspars and for members of the plagioclase series. X-ray work on the potash-soda perthitic felspars has recently been reported by Ito and Inuzuka, by Ito, and by workers in this laboratory, and a preliminary report of an examination of the plagioclase felspars is given in a thesis presented by one of us (S.H.C.) in 1939 for the degree of Ph.D. in the University of Manchester.

The investigations to be described in this paper, as well as those already published from this laboratory, form part of a programme of researches dealing with various aspects of the problem of felspar structure, undertaken in an attempt to obtain a correlation between the physical and chemical properties on the one hand and the details of the structure on the other.

Zinckenite was first described in 1826 by G. Rose, who determined it to be an orthorhombic mineral. The crystals were thought to be seldom single, but to occur in nearly hexagonal forms as a result of twinning in some fashion similar to that found in aragonite. The presence of longitudinal striations on the lateral faces was taken as further evidence that the crystals were twinned. The composition was given by H. Rose as PbSb2S4 or PbS.Sb2S3. The original specimens which were described came from the antimony mine of Woffsberg in the Harz.

In 1922 S. G. Gordon described a new lead sulfantimonite from Oruro, Bolivia, which he named keeleyite. This mineral he presumed to he orthorhombic, although no measurable crystals were found, and the formula was given as Pb2Sb6S11 or 2PbS.3Sb2S3.

The recent finding of a stellerite-like mineral in California has led to this study of its relations to epidesmine and stilbite. The mineral was found by Mr. Allen Nichol, mineralogist of the Division of Highways, in the quarry of the Calavera Materials Company near Oceanside, San Diego County. Some specimens reached the writer through the State Division of Mines. The mineral occurs as sheaf-like clusters of small glistening white crystals in cracks and cavities of andesite. The largest crystals are nearly a quarter of an inch long, but tend to aggregate formation so that they do not lend themselves to accurate goniometric measurement. They are apparently orthorhombic, of tabular habit, showing the three pinakoids and small bright faces of a pyramid. The excellent pinakoid cleavage has a pearly lustre, and if this is taken as (010) the crystals, which show parallel extinction, have the same optical orientation as stellerite.