bluuebunny/crossref_metadata_2025 huggingface dataset:
Note on the occurrence of Strüverite in Perak
Authors: Scrivenor J. B.
Published: December 2006

In a recent number of the Mineralogical Magazine an analysis of strüverite found in perak was published. This mineral was submitted to me by Mr. R. L. Corbett for examination in August, 1909, and as I failed to detect its relation to the Piedmont strüverite described shortly before, the material was forwarded to the Imperial Institute in accordance with an arrangement between the Institute and the Federated Malay States Government. While waiting for the results of the analysis, the locality from which the mineral came was traced and some prospecting work carried out to ascertain the amount of material available. This work afforded information that is of interest concerning the origin of the mineral.
Description of an apparatus for preparing thin-sections of rocks
Authors: Herbert Smith G. F.
Published: December 2006

Early in the year 1912 extensive modifications were introduced in the apparatus for slitting rocks, and for grinding and polishing thin-sections in the Mineral Department of the British Museum, the whole of the alterations and additions being carried out to my designs by Messrs. Plume and Parry, 47 Old Compton Street, London, W. The changes made were chiefly in the means for holding the specimen or section during the operations; much of the actual machinery remained unaltered, and some of it dates back to the initial installation, upwards of forty years ago. It may not, therefore, be without interest if a brief description of the history of the installation be included with the description of the present apparatus.
The mineral collection of Thomas Pennant (1726–1798)
Authors: Campbell Smith W.
Published: December 2006

Thomas Pennant was born at Downing, Whitford, near Holywell, in 1726. A contemporary and correspondent of Linnaeus and Buffon, he is well known to zoologists as a pioneer of British zoology, and to him were addressed the letters of Gilbert White which form the greater part of 'The Natural History and Antiquities of Selborne'. He travelled very extensively in the British Isles and wrote many accounts of his tours, perhaps the best known being his account of London and his 'Tour in Wales'.
(1) The crystal-habit of Topaz from New Brunswick, Canada. (2) A method of silvering crystal-faces for giving improved reflections on the goniometer
Authors: Ellsworth H. V.
Published: December 2006

It is only recently that the mineral topaz has been found in any considerable quantity in Canada. Previous to the discovery of the topaz of York County, New Brunswick, in 1911, it was distinctly a rarity among Canadian minerals and had never been found crystallized in any Canadian locality. The above-mentioned district, however, has yielded both the massive and crystallized varieties in fair abundance and some fairly perfect crystals have been obtained for measurement.
A new stereographic protractor
Authors: Herbert Smith G. F.
Published: December 2006

In the stereographic projection (fig. 1) ABA'B" is the primitive circle, having the same radius a as the corresponding sphere ; ATA'T" is the circle representing a great circle on the sphere inclined at an angle θ to the plane of the projection ; O and C are the centres of the primitive circle and the circle ATA'T' respectively. CO are joined and projected both ways to meet the circles as shown.
A calcium-iron Garnet from China
Authors: Scrivenor J. B.
Published: December 2006

During the earlier half of 1918 Mr. San Ah Wing, a Chinese gentleman residing in Kuala Lumpur, sent me three concentrates of sand for examination. It was thought at first that they came from some part of the Federated Malay States, but the locality proved to be the Yong Choon district of the province of Kwang Tung, China. No information concerning the geology of this district was obtainable, but the association of minerals in the concentrates suggests that they were washed out of detritus derived from calcareous rocks.
An apparatus for cutting crystal-plates and prisms
Authors: Thomas Herbert H. , Smith W. Campbell
Published: December 2006

The apparatus to be described has been designed for the cutting of parallel plates and of prisms of crystallized substances in any required direction. The authors have endeavoured to design a small apparatus, simple in construction and easy to manipulate, which at the same time will be capable of yielding results of sufficient accuracy for most optical work on minerals. Several instruments have been devised with the same objects in view, notably those of E. A. Wülfing, G. Halle~ and F. Stöber. The well-known cutting and grinding goniometer of Dr. Tutton is an instrument of an entirely different class.
Optically uniaxial Augite from Mull
Authors: Hallimond A. F.
Published: December 2006

The mineral hero described was recently collected by the officers of the Geological Survey during their work for the six-inch map of the Island of Mull. It is present as minute phenocrysts in a dark, glassy, magnetite-bearing rock/which is intruded as sheets in the Tertiary lavas nearly one mile south-south-west of Pennygael.

The small rounded crystals of augite are seldom more than ½ mm. in diameter and are traversed by irregular cracks. They contain a few negative crystals, and are occasionally darkened, probably with included magnetite. They appear to have been reabsorbed to some extent by the matrix.
The Meteorites of Uwet, Kota Kota, and Angela : re-determinations of nickel and iron in the Baroti and Wittekrantz meteoric stones
Authors: Prior G. T.
Published: December 2006

Early in 1905 a small fragment of a meteoric iron from Uwet in Southern Nigeria was received at the Imperial Institute from Mr. John Parldnson, the Principal of the Mineral Survey then proceeding in Southern Nigeria. The fragment was part of a large mass which was held in great veneration by the natives of Uwet (lat. 5° 17' p N., long. 8° 15' p E.), a town on the Calabar river, about 23 miles north by west of Calabar. Later, further particulars of the meteorite were communicated to the Imperial Institute by Mr. E. D. Simpson.
On hollow spiral prismatic crystals of ice on the surface of snow
Authors: Leigh Fermor L.
Published: December 2006

Last winter I enjoyed the good fortune of spending some three months at Zweisimmen in the Bernese Oberland of Switzerland, in order to participate in the winter sports. Happily it proved a fine, cold winter of hard frosts and moderately heavy total snowfall. During such a stay in the crisp, dry cold of a snow-mantled world, the manifold and beautiful forms assumed by snow and ice are set before one in a manner impossible in this relatively warm and moist isle with its fleeting glimpses of true wintry weather.
Sur une propriété numérique de l'ensemble des axes de symétrie situés dans les plans de symétrie d'un polyèdre
Authors: Cesàro G.
Published: December 2006

Les axes de symétrie d'un polyèdre ne sont pas toujours situés tous dans ses plans de symétrie ; ainsi, tandis que le cube a tous ses axes

situés dans ses plans de symétrie, le rhomboédre

a son ʌ3 situé dans des plans de symétrie, tandis que les 3L2 ne sont pas situés darts ces plans.
Note on the colours of some alluvial Diamonds
Authors: Mennell F. P.
Published: December 2006

In 1906 the present writer gave a brief account of the interesting alluvial diamond field which is situated on the borders of the Somabula Forest in Southern Rhodesia. The area is not of very great economic importance, but it has nevertheless yielded to date about 10,500 carats of diamonds (valued at over £45,000). These are extracted from thick beds of gravel which, as described in the paper referred to, generally consist of well-rounded pebbles in a matrix of sandy clay.
Detrital Andalusite in Cretaceous and Eocene sands
Authors: Davies G. M.
Published: December 2006

Six years ago, in a paper read before this Society, Dr. Herbert H. Thomas drew attention to the relative abundance of andahsite in the Plioeene deposits of Cornwall, East Anglia, and Kent, and also in various glacial and recent sands. When that paper was written, the only recorded occurrence of unaltered detrital andalusite in sedimentary rocks of greater age than the Pliocene was that in the Middle Chalk of Beer in Devonshire.
The dispersion phenomena of some monoclinic Felspars
Authors: Kôzu K.
Published: December 2006

In the present paper the dispersion of the refractive indices of monoelinie felspars from four different localities is given, likewise that of the optic axial angle and of the optic axes in some of them.

The method of investigation and instruments for these studies have been already mentioned in my previous paper. As the refractive indices and dispersion of the glass hemisphere of the total-reflectometer have not so far been given, I shall in the first place state the way in which they have been determined and their values and the degree of accuracy attainable, for the dispersion of the glass hemisphere differs to au appreciable degree from that of other instruments of the same kind.
Crystallographic relations of allied substances traced by means of the law of valency-volumes
Authors: Barlow W.
Published: December 2006

A Word of explanatiou as to the nature of valency-volumes : The existence of the law of valency-volumes involves the conclusion that each chemical atom in a crystal has its own special domain throughout which its influence is predominant as compared with that of any other atom. According to this conception the entire space occupied by the crystal can be regarded as portioned out among its constituent atoms, each atom having a cell allotted to it the boundaries of which consist of points at which the influence of some one or more neighbouring atoms is equal to that of the selected atom; thus no interstices are left between the cells.
Démonstration simple de la loi de Miller
Authors: Cesàro G.
Published: December 2006

Lemme. Dans tout triangle, l'arc x (fig. 1), qui mené du sommet partage la base en deux segments α et β, est donné par
The crystallography and dehydration of Torbernite
Authors: Hallimond A. F.
Published: December 2006

Measurements for torbernite have been given by numerous observers; the results are, however, of rather early date, and althoug the values for the ratio a:c are generally in fair agreement with the results here stated, the degree of accuracy of these measurements is not always indicated. Moreover, sevelml minor difficulties arise, add it has been suggested that some of the early descriptions refer to the allied species, zeunerite ; both species are optically uniaxial and possess almost the same axial ratios; they can, however, be distinguished by means of their refractive indices.
Crystals of iron phosphide (Rhabdite) from a blastfurnace
Authors: Spencer L. J.
Published: December 2006

The crystals here described were sent by Dr. J. E. Stead, F.R.S., for crystallographic determination. They came from a 'bear' or mass of metal weighing about 800 tons that had solidified at the bottom of one of the blast-furnaces of Messrs. Cochrane & Co., Ltd., at Ormesby, near Middlesborough. They are present only in sparing amount in drusy cavities, and are absent in the mass of metal itself.
The Meteoric Stones of Launton, Warbreccan, Cronstad, Daniel's Kuil, Khairpur, and Soko-Banja
Authors: Prior G. T.
Published: December 2006

The investigation of the Launton, Warbreccan, and Cronstad meteorites was undertaken with the object of placing on record descriptions of these stones. Launton and Warbreccan were found to conform very well with the type of Baroti and Wittekrantz, containing from 7-9 per cent. of nickel-iron, described in a previous paper. Cronstad, however, which contained as much as 18 per cent. of nickel-iron, showed so much variation from that type as to suggest a passage towards the rare Hvittis class of chrondritic stone containing even larger amounts of nickel-iron.
The isolation of the directions-image of small objects
Authors: William Evans John
Published: December 2006

There are two distinct kinds of image which are the subject of optical investigation: object-images, in which the form of the object is reproduced, and directions-images, in which every point represents a direction followed by light before reaching the objective. An instrument that shows a directions-image may be described as a hodoscope. It is focused not on the object but on infinity, so that parallel rays are collected at the same point in the image.
Spencerite, a new Zinc Phosphate from British Columbia
Authors: Walker T. L.
Published: December 2006

The mineral described in this paper occurs at tile Hudson Bay zinc mine about five miles east of Saline, near Nelson in the West Kootenay district of British Columbia, I regret that I have no data as to the exact character of the ore-body except that it occurs in a region where palaeozoic rocks are intruded by biotite-granite and that it is probably genetically connected with the intrusion of the latter. The zinc occurs ill the form of the silicate and tb a less extent the carbonate. There is also a small amount of oxidized lead-ore, principally cerussite.
Palaeophysiology : the organic origin of some minerals occurring in sedimentary rocks
Authors: Samoilov J. V.
Published: December 2006

During the last few years I have applied myself to the study of some minerals occurring in the sedimentary rocks of a definite geological horizon. The success of my investigations was greatly favoured by the fact that the mineralogical material was collected during the course of the systematic geological exploration of the phosphate deposits of Russia, which during the past eight years has been under my immediate supervision.

The explorations just mentioned were begun in the north-eastern part of European Russia, and several occurrences of barite were found in the first year during the field study of the phosphate deposits in the government of Kostroma.
The crystallization of Parahopeite
Authors: Levovx A. , Walker T. L. , Wheatley A. C.
Published: December 2006

This species, a hydrous zinc phosphate, Zn3P2O8.4H2O, dimorphous with hopeite, was first described by Spencer in 1907. While the material then available was suitable for the physical and chemical description of the new mineral, it did not permit a full crystallographic investigation. Spencer noted that the crystals resembled in a general way those of hemimorphite, and made sufficient measurements to indicate the triclinic character of the mineral. In his sketch of a crystal he indicates that the mineral is twinned, and that this twinning is best seen on the perfect cleavage which is parallel to the brachypinacoid.
On Tapiolite in the Pilbara goldfield, Western Australia
Authors: Simpson Edward S.
Published: December 2006

The Pilbara goldfield lies in the north-west division of Western Australia within the tropics, and has been described in considerable detail by A. Gibb Maitland in Bulletin 40 of the Geological Survey of Western Australia. Though the chief mineral product at present is gold, the district abounds in other economic minerals, notably ores of copper and tin, and has already become famous as being by far the most important producer of tantalum in the world, the chief source of supply of this metal being the manganotantalite of Wodgina.
The use of the orthographic projection in crystallography
Authors: Hilton Harold
Published: December 2006

The geometrical representation of the faces and edges of a crystal is obtained (i) by drawing lines through a fixed point O perpendicular to each crystal-face meeting a fixed sphere with centre O in a point (face-pole) representing that face, (ii) by drawing lines through O parallel to each crystal-edge meeting the sphere in a point (edge-pole) representing that edge. This representation is inconvenient as being in three dimensions, and therefore it is customary to map the sphere on a plane. This is usually done by means of the stereographic or gnomonic projection.
Magnesian Tourmaline from Renfrew, Ontario
Authors: Bruce E. L.
Published: December 2006

The specimens of the mineral examined were obtained from a limestone quarry near the town of Renfrew. The tourmaline occurs near the contact of grey granite-gneiss and crystalline limestone of the Grenville series. The gneiss is intrusive into the limestone, and contact effects are observable both in the intrusive and in the intruded rock. The gneiss consists of quartz, plagioclase, micrccline, and a green pyroxene. The limestone is composed (almost entirely) of calcite, but contains some graphite. The secondary minerals occurring in both limestone and gneiss are, besides the tourmaline, pyrrhotite, titanite, and muscovite.
The relation between different laws of twinning that result in the same twin-crystal
Authors: Evans John William
Published: December 2006

In the following notes I have endeavoured to give in a convenient and simple form a complete account of the relations connecting different twinning-laws or operations, which, when applied to the same crystal-structure, produce indistinguishable results.

A rigorous analysis of the possible relations between the compound structures of twin-crystals, based on the principles of the equality of the structural distances in the plane of composition, will be found in the author's papers, ' The geometry of twin-crystals' (Proc. Roy. Soc. Edinburgh, 1912-1918, vol. xxxii, pp. 416-432, 433-457) and 'Die Geometrie der Zwillingskrystalle' (Zeits. Kryst. Min., 1918, vol. lii, pp. 827-371). See also the paper 'Twin-planes and cross-planes' in this Magazine (1910, vol. xv, pp. 390-397).
On cleavage-angle in a random section of a crystal
Authors: Hilton Harold
Published: December 2006

Suppose a crystal has two good cleavages, and that a thin section is cut in a random direction. Cleavage-cracks are seen in the section which consist of two sets of parallel lines inclined at an acute angle ϕ, which may have any value whatever, depending on the direction in which the section is cut. The question suggests itself: what is the chance that ϕ may lie between assigned limits? This question proves to be incapable of a direct mathematical solution, but it can be solved graphically. This is worked out here for two typical cases, and the general method of performing the graphical solution in every case is indicated.
On the use of the gnomonic projection in the calculation of crystals
Authors: Herbert Smith G. F.
Published: December 2006

Considered from the crystallographical point of view the outstanding feature of the gnomonic projection is the fact that all great circles on the sphere, and consequently all zones on the crystal, appear on the diagram as straight lines. In order to secure its full advantages, it is necessary to take the plane of the paper at right angles to the axis of a zone, and preferably one of the principal zones of symmetry on the crystal.
Semseyite from Dumfriesshire
Authors: Herbert Smith G. F. , Prior G. T.
Published: December 2006

Early in the year 1918 Mr. Atehur Russell picked up at the old antimony-lead mine at Glendilming in Eskdale, Dumfriesshire, Ipecimens of the antimony-lead ore Jound there, in which were small cavities lined with a drusy layer of mimlte crystals; these, being markedly deeper in eolour than the stibnite forming part of some of the specimens, belonged to a different species, and probably a sulphantimonite of lead. Mr. Russell blought some of the specimens to the Museum, and some of the small crystals were examined with the view of determining the species to which they belong.
A lead-grey, fibrous mineral from the Binn valley, Switzerland
Authors: Solly R. H.
Published: December 2006

In a paper published many years ago the following passage occurs under the section treating of seligmannite :—'Mingled with the se]igmannite, and partially coating the baumhauerite, are a number of very fine needles of a lead-grey colour, the nature of which I have as yet been unable to determine.' These needles form the subject of the present paper.
The crystallography of Vogtite, an anorthic metasilicate of iron, calcium, manganese, and magnesium, from acid steel-furaace slags
Authors: Hallimond A. F.
Published: December 2006

The substance was met with in the course of work on steel-furnace slags, a general account of which has been communicated to the Iron and Steel Institute. These slags were for the most part melts consisting principally of the three oxides FeO, MnO, and SiO2, and yielded the silicates fayalite and rhodonite. The small amount of calcium silicate usually present is held in isomorphous solid solution ill these silicates, but when the amount of lime exceeds about eight per cent. a new silicate appears, which does not seem to belong to any of the known mineral groups.
Siliceous sinter from Lustleigh, Devon
Authors: Edge A. B.
Published: December 2006

The district round Lustleigh, near Bovey Tracey, is mined on a small scale for a very fine quality of micaceous haematite, which occurs there in well-defined lodes traversing the granite. This soft and powdery variety of haematite, known both locally and in the trade as ‘shining ore’, is used for a variety of purposes, but principally as the basis of a rust-proof paint. The ore and its mode of occurrence have been briefly described by J. S. Martin, and for the purpose of this short paper no fm4her description of the mines in general will be necessary.
Villamaninite, a new mineral
Authors: Schoeller W. R. , Powell A. R.
Published: December 2006

Early in 1914 a parcel of copper-nickel-cobalt ore, weighing several tons, was received in London for valuation from the 'Cármenes mine, Spain'. This somewhat vague statement of locality refers without doubt to the group of mines in the district of Cármenes, province of León, situated about 6 km. E.N.E. of Viilamanín, a statisn on the railway from Gijon to León and about 40 km. N. of the latter city. The ores of these mines are described as consisting of sulphide minerals of copper, cobalt, and nickel in a gangue of dolomite.
A graphic method for the comparison of minerals with four variable components rearming two isomorlohous pairs
Authors: Simpson Edward S.
Published: December 2006

Graphic methods are often of the greatest assistance in bringing out the affinities of closely related minerals and particularly of members of isomorphous series. An illustration of the use of such a method in the case of a series involving three variables, all of them mutually replaceab]e, has already been given by the author in dealing with minerals of the tapiolite-mossite-rutile series. Recently, in studying a mineral of the spinel group, occurring in serpentine country near Namban, in the South-Western Division of Western Australia, it was found convenient to use a graphic method to bring out its relationship to the type minerals spinel, hercynite, and chromite, and to the intermediate minerals previously described under the names of picotite, chrompicotite, magnesiochromite, and magnochromite.
Fibrolite (= Sillimanite) as a gem-stone from Burma and Ceylon
Authors: Spencer L. J.
Published: December 2006

The only book on precious stones in which fibrolite is taken into account appears to be that of .J. Escard, ‘Les pierres précieuses’ (Paris, 1914, p. 190). He mentions the prehistoric stone implements made of dense fibrolite tbund in France, ~nd also states that the mineral is sometimes used as an ornameutal stone. Examples of such material are represented in ttm British :Museum collection of minerals by: a hatchet, measuring 11×½ cm., of pale yellowish-grey, compact fibrolite from N.W. France ; and a polished knife-handle, 9 cm. long, of greyish-white, transluceut, fibrous material with silky lustre. Clear material of good colour and cut in the form of a faceted gem has not hitherto been described.
On Cornetite from Bwana Mkubwa, Northern Rhodesia
Authors: Hutchinson A. , MacGregor A. M.
Published: December 2006

The mineral to be described in the following pages was found hy Mr. J. L. Popham in 1910 at Bwana Mkubwa, Northern Rhodesia, and was sent by him to Mr. A. E. V. Zealley, at that time Curator of the Rhodesia Museum, Bulawayo. Investigations conducted by one of us (A. M. M.) in Bulawayo showed that the mineral occurred as definite, though minute, orthorhombic crystals and that it consisted in the main of copper and phosphoric acid, but that it differed in many respects from the known hydrated copper phosphates such as libethenite, tngilitc, dihydrite, or pseudomalachite.
Density, refractivity, and composition relations of some natural glasses
Authors: Tilley C. E.
Published: December 2006

Whilst some atention has in the past been devoted to the question of the properties of natural glasses, very little has been done to indicate the interrelations of the properties determined. In the case of tile natural volcanic glasses, this is unfortullately only too evident from a study of the standard text-books. A determination of such properties as density, refractivity, ttud chemical composition, and the interrelations of these for particular glasses, is rarely to be found in the literature. The chief contribution to this subject is due to Stark, who has examined the refringence of a large number of volcanic glasses. Unfortunately, there is no record of the density of these rocks, and the interrelation of these remained unknown.
A simplification of the Rosiwal method of micrometric analysis
Authors: Alfred Richardson W.
Published: December 2006

Johannsen has recently described an areal method of micrometric analysis, based on the use of a planimeter in conjunction with a drawing apparatus. It is claimed that this method results in some increase of accuracy, a considerable saving in time, and—most important of all—eliminates all the eye-strain due to continuous reading of a micrometer.
A note on crystallographic notation
Authors: Hilton Harold
Published: December 2006

There exists a bewildering variety of notations for the thirty-two classes of crystal-symmetry and for the 230 groups of symmetry-movements which control the arrangements of atoms building up a crystalline medium. The notation which has found most favour has been that of Schoenflies's ' Krystallsysteme und Krystallstructur ' (1891). This was followed in Hilton's ' Mathematical Crystallography ' (1903) (see the second column of the table given below), and more recently in Niggli's 'Geometrische Kristallographie des Diskontinuums' (1919).
On some crystallized sulphates from the province of Huelva, Spain
Authors: Collins Henry F.
Published: December 2006

The occurrence of melanterite, pisanite, and chalcanthite as secondary minerals resulting from the oxidation of pyrites masses containing copper is well known. It is not so well known that other metallic sulphates are from time to time found, and a brief description of the mode of occurrence of a few of these, in addition to some details of the composition of pisanite and chalcanflSte, may be of interest.

Pisanite.—This mineral is of common occurrence at all the pyrites mines of Huelva and elsewhere, ibrming stalactites and stalagmites in those parts of the mines that are above drainage level though subject to more or less percolation of water. It is rarely found as well-formed crystals, save occasionally when a pool ef strong sulphate water has been temporarily dammed hack in some way, and then supersaturated through evaporation.
The Dartmoor granite: its mineralogy, structure, and petrology
Authors: Brammall Alfred , Harwood H. F.
Published: December 2006

This paper continues the study of the constituent minerals of the Dartmoor granite. The district to which it mainly refers comprises the for-area around Widecombe and a part of the aureole adjoining. No detailed reference will be made at this stage to aureole phenomena. The results to be recorded necessitate a brief description of the two main granite types and of their field relationships. Abundant varieties and modifications of both types occur, but for the Purposes of the present paper they are of subordinate importance.

Most of the for-masses and high-level exposures of granite in the area consist in the main of the type known locally as the ‘giant granite‘ — a very coarse-grained, strongly porphyritic roelc rich in biotite, and consistently garnetiferous; it has an index-figure 1 ranging from 7.5 to 12.
On a peculiar chlorite-rock at Ible, Derbyshire
Authors: Garnett Cecil S.
Published: December 2006

In this paper is described an apparently hitherto scientifically unnoticed mode of alteration of olivine-dolerite in the intrusive sill at Ible near Matlock.

The igneous rocks of Derbyshire, locally called ‘toadstones’, constitute a well-known basic series of both contemporaneous and intrusive rocks. They comprise lava-flows, sills, a few thin dikes, agglomerates, and tufts. All occur in beds of Lower Carhoniferous age, and are confined to the upper half of the known thickness of the Carboniferous Limestone, with, in the south of the county, the overlying Limestone Shales. They have been described, in recent years, by Sir A. Geikie (‘Ancient Volcanoes of Great Britain’, 1897, vol. 2); II. H. Arnold-Bemrose (Quart. Journ. Geol. Sot., 1894, vol. 50, pp. 603-644; 1907, vol. 63, p. 241, et seq.); and H. C. Sargent (ibid., 1918, vol. 73, pp. 11-25).
The graphical determination of the constants of a shear
Authors: Hilton Harold
Published: December 2006

Recently A. Johnsen has given a graphical solution by means of the stereographic projection of the problem of determining the constants of a homogeneous shear of a crystal, knowing the initial and final indices of two faces or two edges.

The same problem may be solved more easily by means of the gnomonic projection.
On the occurrence of petalite and pneumatolytic apatite in the Meldon aplite, Okehampton, Devonshire
Authors: McLintock W. F. P.
Published: December 2006

The Meldon aplite is a small intrusion lying to the north-west of the Dartmoor granite about two miles south-west of Okehampton. Its microscopic characters were investigated by Sir Jethro Teall, whilst the geology of the district, with petrological accounts of the aplite and its associated rocks, has been fully dealt with by R. H. Worth, who notes the presence of felspar, quartz, mica, tourmaline, topaz, apafite, fluor-spar, montmorillonite, and axlnite.
The ‘toadstone-clays’ of Derbyshire
Authors: Garnett Cecil S.
Published: December 2006

At many places in ‘The Peak District’ of Derbyshire, the igneous rocks, locally called ‘toadstones’, have, to varying extents, suffered an alteration with, as a result, the production of clays—locally called ‘toadstone-clay’. These clays attracted the attention of the present author some years ago, and since that time, whilst conducting extensive ‘field’ investigations in the course of a survey of the minerals of Derbyshire, observations on them have been ahnost continuously made and the deductions drawn therefrom carefully considered.
On the genesis of Widmanstätten structure in meteorites and in iron-nickel and iron-carbon alloys
Authors: Belaiew N. T.
Published: December 2006

In April 1909 a paper on artificial reproduction of meteoric structure in alloys of iron aud carbon was read by the author before the Russian Mineralogical Society. In that paper special reference was made to the work of Sorby, who, to cite his own words, for ‘more than twenty years … commenced to carefully study the microscopical structure of iron and steel in order, if possible, to throw light on the origin of meteoric iron’. A brief survey of the work of Stodart and Faraday, of Osmond, Rinne, and Berwerth was also given and, subsequently, the structure of a carbon-steel containing 0.55 % carbon with perfectly developed Widmanstätten figures was described.
On stilpnomelane from North Wales
Authors: Hallimond A. F.
Published: December 2006

Pisolitic ironstones occur at various localities in North Wales, at about the horizon of Nemagraptus gracilis. The rocks have undergone considerable folding and the hard ironstones are often faulted and in many cases deformed. Greenstone dikes frequently intersect the beds, usually with little visible alteration of the ore, though the ironstones are generally hardened, with incipient re-crystallization of the chamosite. At Pen-y-rallt iron mine, situated half a mile east of Llanfrothen church near Penrhyndreudraeth in Merionethshire, a steeply inclined pisolitic ironstone bed rests upon a mass of igneous rock; and here the alteration of the ore is in a more advanced stage, for the ironstone is in places seamed with roughly parallel asbestiform veins (up to 1 inch) which contain a brittle dark-brown mineral strongly resembling biotite ; the centre of the vein is sometimes filled with chalybite.
A graphical method for the rapid correction of specific gravity determinations
Authors: Hutchinson A.
Published: December 2006

It has long been recognized that if specific gravity determinations are to be accurate to a unit or two of the third decimal place corrections must be applied for the error due to the circumstances (i) that the weighings are made in air instead of in a vacuum, and (ii) that the temperature at which the determinations are made usually differs considerably from the standard temperature of 4° C.
Topaz from Cornwall, with an account of its localities
Authors: Russell Arthur
Published: December 2006

Topaz, so common an accessory in tin lodes in all parts of the world, has hitherto been looked upon as comparatively rare in Cornwall. When massive, or even in the form of small, well-developed crystals, it is a mineral easily overlooked, or apt cursorily to be mistakcn for quartz.

The presence of topaz as a microscopic accessory in granite, greisen, and rarely elvans, from most of the Cornish masses, has been determined by Dr. J. S. Flett in the course of the work of the Geological Survey; while the late Mr. J. H. Collins was responsible for the record of other interesting localities.

In the present notes I have collected all the available information respecting its mode of occurrence and localities ; and have added several new ones, at some of which the mineral occurs in considerable mass, thus affording evidence that topaz is in Cornwall, as in the case of other countries, a comparatively common associate of cassiterite and wolframite, both in granite and sedimentary rocks.
Note on cordierite in a cordierite-gneiss from Madura district, Madras, India
Authors: Krishnan M. S.
Published: December 2006

The specimen of cordierite-gneiss under notice was collected by Mr. T. N. Muthuswami (Assistant Professor of Geology, Presidency College, Madras) in a quarry at Ganguvarpatti in the Madura district. On examining tliin sections of the rock, he found that many of the cordierite crystals were optically positive, and, thinking that the mineral might be worth further investigation, he sent a specimen of the rock to me. The investigation was carried out ill the Geological Department of the Imperial College of Science and Technology, and my thanks are due to Professor W. W. Watts and Dr. J. W. Evans for their kindness in affording me facilities for this work and also to Dr. H. H. Thomas, of H.M. Geological Survey, for his kindness in placing Fedorov's universal stage at my disposal for the measurement of the optic axial angle.
Biographical notices of mineralogists recently deceased. (Second series)
Authors: Spencer L. J.
Published: December 2006

Short biographical notices of persons interested in scientific mineralogy have been given in this Magazine since 1876. In the last volume these were more systematically collected together and indexed for convenience of reference and permanent record. For a continuation of this series the various details have been collected and filed during the past three years. I have to thank several foreign correspondents for kindly supplying some of the less readily accessible information; in particular, Professor P. N. Chirvinsky, of Novocherkassk in the Don region.

The present list includes 55 haines, for 49 of which dates of birth and death, or ages, are here recorded. Including these with the 254 previously recorded in this Magazine, the total is 308 lives for which ages are known. The average age for these 303 lives of mineralogists is 64 years.
On the chemical classification of the mica group. I. The acid micas
Authors: Hallimond A. F.
Published: December 2006

In a discussion of the composition of glauconite, it was shown that the analyses of this substance can be represented in terms of simple molecular proportions, provided that the mineral is regarded as a mixture of a silicate containing the group R2O3 with a similar compound in which one equivalent of R2O8 is replaced with one equivalent of RO; the general formula being R2O. 4(R2O3, RO). 10SiO2. nH2O.

Work on the sedimentary iron ores collected during the preparation of the ‘Special Reports on Mineral Resources’, recently issued by the Geological Survey, made it necessary to review the composition of some of the chlorites ; but no evidence of similar replacement was found among the better-known minerals of that group.
Tourmalinization in the Dartmoor granite
Authors: Brammall A. , Harwood H. F.
Published: December 2006

On the basis of field relationships, the main types of the Dartmoor granite can be referred to four stages of intrusion, the sequence being from relatively basic to thoroughly acid.

To this sequence is closely related an increase in the content of tourmaline and in the extent to which autopneumatolysis (with tourmalinization) was effective before solidification of the rock was complete.

Autopneumatolysis is well displayed by many minor intrusions referred to the latest stage. Such an intrusive rock is reddened more or less uniformly throughout its entire mass, and volatile constituents exhaled from its margin have reddened a contact-zone of the grey granite into which it is intrusive.
Potash-oligoclase from Mt. Erebus, Antarctic, and anorthoclase from Mt. Kenya, East Africa
Authors: Mountain E. D.
Published: December 2006

A Fine set of loose crystals of felspar from Mt. Erebus was collected by Mr. F. Debenham on the British Antarctic (‘Terra Nova’) Expedition in 1910, and was acquired by the British Museum (Natural History) with the collection of rocks obtained on that voyage. These crystals are found in great profusion on the crater slopes, and their occurrence has been briefly described by David and Priestley, who referred to them as anorthoclase. On ascending the inclined floor of the second crater they saw ‘that the covering of snow became thinner until it almost entirely disappeared, being replaced by a surface formed of crystals of anorthoclase felspar from half an inch to four inches in length’.
The crystalline structure of pentaerythritol tetranitrate
Authors: Ellie Knaggs I.
Published: December 2006

Pentaerythritol tetranitrate, C(CH2ONO2)4, is an interesting compound structurally, since there is, in the molecule, a carbon atom with foul' like groups (–CH2ONO2) attached to it. The molecule is therefore of the type CX4. It was hoped that an examination of the crystals by means of X-rays would show how far the molecule retains its form and symmetry in the crystalline state ; also that some light would be thrown on the configuration of the nitro- (–NO2) group, especially the equivalence or otherwise of the two oxygen atoms of the group—a question which it has not yet been found possible to settle by chemical methods.
Illustration and detection of inclined and horizontal dispersion in biaxial crystals
Authors: Wilberforce L. R.
Published: December 2006

As it is not always easy to obtain for the use of students suitable specimens of crystals which exhibit inclined or horizontal dispersion of the mean lines to a marked extent, a ready method of artificially producing optic pictures which show the appearances characteristic of these dispersions may be found of service by teachers.

It is ohvious that, if the optic picture of an ordinary biaxial crystal is viewed or projected through a prism whose refracting edge is either parallel or perpendicular to the axial plane of the crystal, the dispersion produced by the prism will displace the components of the optic picture due to the various colours of the spectrum through distances increasing from red to violet, and will thus reproduce the phenomena of horizontal and inclined dispersion respectively.
The use of alignment charts in crystal-optics
Authors: Hutchinson A.
Published: December 2006

The widespread use of methods based oil total-reflection for finding the refractive indices of crystals either directly, by the Abbe-Czapski crystal reflectometer or by the Kohlrausch method, or indirectly by means of liquid mixture of known refractive intex which require to be verified and standardized from time to time, renders desirable a rapid graphical method of ascertaining with some accuracy the index of the substance under test, direct from the instrumental data without calculation.

An attempt in this direction was made by the author some years ago. The equation to be solved is n' = n sin θ, where n' is the index to be found, n that of the glass hemisphere, prism, or highly refracting liquid employed in the total-reflectometer, and θ the critical angle of total-reflection observed.
The use of the stereographic protractor for the interpretation of Laue crystal-photographs
Authors: Hutchinson A.
Published: December 2006

The spots of a Laue crystal-photograph may be regarded as due to the reflection of X-radiation by the planes of the crystal and the interpretation of these photographs involves the determination of the index of the plane by which any given spot is produced. This 'interpretation can be readily accomplished by two distinct though related methods. We may, in the first place, utilize the stereographic projection and determine the indices of the planes by means of intersecting zone- circles. This method, the earliest in point of time, was explained by W. L. Bragg in 1913. In recent years, however, it has become usual to employ for this purpoee the gnomonic projection which affords a solution in some respects impler and more direct than the stereographic method used by Bragg, and detailed illustrations of its application in this field have been given by R. W. G. Wyckoff, and E. Schiebold.
Gold and silver in the Dartmoor granite
Authors: Brammall A.
Published: December 2006

Gold and silver have been detected not only in the peculiar facies of the granite occurring on Bittleford Down, but also in the normal grey biotite-granite of numerous tor- and quarry-localities; several hand-specimens of granite showing minute flakes of visible gold have been collected.

The modes of occurrence of gold on Dartmoor, the environment of the granite from which specimens showing visible gold have been taken, and the gold-silver content of the granite generally have been investigated in some detail, with the results described below.
Some mineralogical transformations in crystalline schists
Authors: Tilley C. E.
Published: December 2006

The twofold division of metamorphic rock-series into (a) Isophysical rock-series and (b) Isochemical rock-series, as proposed by P. Niggli in his paper, 'Die Gesteinsassoziationen und ihre Entstehung', introduces into metamorphic petrology two very useful terms, which will be of service in the metamorphic researches that await the attention of the petrologist.

Among such investigated rock-series one may call to mind the studies on the chloritoid-schists of the St. Gotthard massif," the glaucophaneschist suite of the Bagne valley (Wallis), the calc-silicate series of the Trondhjem region, the contact rocks of the Kristiania and Comrie areas. Of these the last are particularly illustrative of an isophysical rock-series, wherein a chemically wide group of assemblages conforming to the composition of shale-limestone sediments is represented in the free-silica and quartzless hornfelses.
The anomalous optical properties of some new series of isomorphous double tartrates
Authors: Buckley Harold E.
Published: December 2006

In a previous paper two well-known crystalline compounds, sodiumpotassium tartrate, XaKC4H4O6. 4H2O, and sodium-ammonium tartrate, Na(NH4)C4H4O6.4H2O, were described, and it was therein shown how, in the crystals obtained by mixing these two isomorphous substances in any proportion, the dispersions of the ojjtic axes in the freshly prepared crystals were incompatible with orthorhombic symmetry. The crystals have been frequently measured and found to be orthorhombic bisphenoidal in external symmetry and this has been further confirmed by the author's measurements. A. full description of all the various dispersions to be found in the orthorhombic and monoclinic systems may be obtained from any text-book of crystallography, but in the following pages two of these are specially important.
Sperrylite crystals from the Transvaal
Authors: Spencer L. J.
Published: December 2006

A very fine and unusual crystal of sperrylite, recently presented by Mr. G. H. Beatty of Johannesburg to the mineral collection of the British Museum, came from a new adit on the Tweefontein farm (no. 1083), about 10 miles NNW. of Potgietersrust, Waterberg district, Transvaal. It had been found embedded in copper-stained limonite in crush-zones of banded ironstone underlying norite. The limonite matrix is presumably an alteration-product of sulphides (pyrrhotine, pentlandite, and chalcopyrite). The banded ironstone is an altered sediment belonging to the dolomite series, and is penetrated by apophyses from the basic margin of the Bushveld igneous complex.
Aramayoite, a new mineral, from Bolivia
Authors: Spencer L. J.
Published: December 2006

Bolivian minerals have been sent tbr examination and preservation in the British Museum oolleetiml at various times since 1894 by my old school-fellow Mr. Malcolm Robmts, A.R.S.M., now General ganager of the Compagnie Aramayo de Mines en Bolivie. Several of these have been described in the pages of this magazine (see vol. 14, p. 309). Although he has industriously collected Bolivian minerals for over thirty years he is only now rewarded by the discovery of a species new to science. The material which he has been good enough to entrust to me for description was recognized by him as being probably something new, and this was confirmed by a chemical analysis made by Mr. T. Burns MeGhie in the assay office at Quechisla in Bolivia.
On the chemical classification of the mica group. III. The molecular volumes
Authors: Hallimond A. F.
Published: December 2006

It is unfortunate that so many published analyses of mica are not accompanied by the physical data for the material used. Nevertheless, enough information is available to permit a general comparison of the density relations for the group. This is most conveniently made in terms of the specific volume, for, in most isomorphous series, the volume is an additive property eveu when the molecular volumes of the endminerals differ appreciably. Such a relationship will be shown to hold good approximately for the micas; the volume can be calculated from constants assigned to the constituent oxides, the difference from the observed value being rarely more than 2 per cent.
Rotating crystal X-Ray photographs
Authors: Greenwood Gilbert
Published: December 2006

Since the original experiments of M. von Laue on the diffraction of X-rays by crystals, other and more suitable methods of research have been devised. The Bragg ionization-chamber method and the Debye-Scherrer powder method are now quite well known. The newest technique is that of the so-called 'rotating crystal', which is based essentially on some experiments of M. de Broglie. This method was first employed and developed in the Kaiser Wilhehm Institut für Faserstoffchemie in Berlin. It has recently been extended by the work of J. D. Bernal in the Royal Institution in London.

There are two methods of making this type of photograph. In both a small crystal is rotated in a beam of X-rays and the reflected beams recorded photographically, in one case on a flat plate, and in the other on a cylindrical film the axis of which coincides with the axis about which the crystal is rotated.