bluuebunny/crossref_metadata_2025 huggingface dataset:
An inclusion of magnetite in diamond
Authors: Spencer L. J.
Published: December 2006

A Minute, black fragment of material, taken by Dr. J. R. Sutton from a cavity exposed on a cleavage-surface of a colourless diamond from Bultfontein mine, Kimberley, South Africa, was sent by him for determination. It is black with a sub-metallic lustre and in parts a bronzed tarnish; and is quite opaque even on the edges. The form is roughly that of a triangular chip, measuring 11/2 by 11/4 mm. with a greatest thickness of about 1/2 mm. The weight is about 1 milligram. Tile surface shows a small and uneven to granular fracture. On one portion there is a good crystal-face which reflects a sharp image ; and on one part of this face there is a stepped growth with striae at 60°.
The dissociation of dolomite. II
Authors: Garnett Cecil S.
Published: December 2006

In this paper further evidence is put forward in support of a previous paper on the subject. Very soon after the reading of that paper, A. E. Mitchell read a paper before the Chemical Society on a closely related subject. Working quite independently, and employing other methods of investigation, Mitchell arrived at conclusions in close agreement with those detailed in the former paper. H.L.J. Bäckström has criticized Mitchell's paper, raising some objections 'against the experimental evidence produced aud the … way of interpreting it'. Where Bäckström objections touch on anything in Mitchell's paper which is incidentally akin to any of the work described in this or the earlier paper, they will be discussed herein.
On the Chemical Classification of the Mica Group. II. The Basic Micas
Authors: Hallimond A. F.
Published: December 2006

In the first part of this paper it was shown that the acid section of the mica group could be divided into two main series, the potash micas and the lithia micas. The molecular ratio of potash to silica was 1 : 6 and the micas were therefore represented as salts of an acid characterized by this value. The present section contains the result of a similar investigation of the basic micas, especially biotite and phlogopite; here again it will be seen that the grouping K2O. 6SiO2 is present throughout. For comparison of the molecular composition, the analyses of the basic micas have been recalculated in molecular ratios, (Si,Ti)O2 being made equal to 600 according to the method already used for the acid micas.
The crystalline structure of zircon
Authors: Binks W.
Published: December 2006

In a proper recently published by Prof. Vegard is contained an analysis of the structure of the zircon group of crystals, which belong to the tetragonal holohedral class, the axial ratio being approximately a : c = 1 : 0.656.

As the present work was completed when the above paper appeared, it is interesting to find that the principal deductions concerning the structure of zircon, ZrSiO4, are confirmatory. The parametral values are, however, slightly different. This difference, though small in itself, is found to introduce larger discrepancies between the observed and calculated intensities of reflection.
Three South African meteorites: Vaalbult, Witklip, and Queens Mercy
Authors: Prior G.T.
Published: December 2006

Small portion (B.M. 1921, 274) of the Vaalbult meteoric iron, weighing about 184 grams, was kindly placed at the disposal of the writer for examination by the late Dr. L. Peringuey, Director of the South African Museum, Cape Town. According to information received from him, this meteorite is known as the 'Vaalbult' siderite, and was presented to the South Afican Museum on April 22, 1918, by Mr. S. Grove, Member of the Provincial Council of the Cape for the Prieska Division, who obtained it from Mr. Japie Greeff, the owner of the farm on which it was found, probably early in the same year. The original mass weighed about 26 lb. and was very deeply and broadly pitted. In external appearance it is somewhat similar to the large (1,210 lb.) Ratteldraai iron from the Kenhardt Division, more than 60 miles distant, found in 1909. A cast of the iron sent by Dr. Peringuey shows that it is of very irregular shape.
On β-quartz twins from Some Cornish localities (With Plates VIII and IX.)
Authors: Drugman Julien
Published: December 2006

In their paper on 'The structure of α and β quartz', Sir William Bragg and R. E. Gibbs touch on the question of twinning of quartz, showing how X-ray determination of structure can help to explain the different types of twinning. They only mention, however, twinning with parallel axes and twinning on . It would be interesting to see this extended to the examination of all known laws of twinning of α-and β-quartz. There is, however, still much doubt about the laws of the twinning of quartz. Many varieties of twins have been described, but a number of these are much open to doubt, while some are decidedly nonexistent. G. Friedel has within recent years published valuable papers on the laws of twinning in general, and has made more special application of his theories to the laws of twinning of quartz. It would be interesting to see how far all cases of well-established quartz twins occurring ill nature confirm his results.
A simple and accurate constant-volume pyknometer for specific gravity determinations
Authors: Ellsworth H. V.
Published: December 2006

Experience with the usual types of glass pyknometers long ago convinced the writer that these instruments as ordinarily used are subject to considerable errors and may be quite unreliable when dealing with small quantities of material, It is true there are forms intended to be used in conjunction with a very precisely regulated water-bath which are capable of giving results of high accuracy, but this method of determination at constant temperature involves too much time and trouble for routine mineralogical work. But no matter what the design of glass pyknometers, and their variety is legion, in actual practice they suffer in common from tile defects of the material of which they are constructed.

The heavy-solution method is inconvenient ; it cannot be used for the heavier materials and there is often danger of contaminating the material which may be intended for analysis.
The identification of dumortierite as grains; dumortierite in Cornish granite
Authors: Groves A. W.
Published: December 2006

The following notes are intended to bring to the notice of workers on heavy mineral grains the possible confusion between blue tourmaline, purple tourmaline, glaucophane, lepidolite, andalusite, pleochroic sillimanite, and dumortierite. Dumortierite (when blue) is very liable to be passed over as the more common mineral glaucophane, the optical properties of the cleavage-flakes of these minerals being similar in several respects.

Having seen a grain of dumortierite from the Wealden of Surrey, kindly lent me by Mr. H. A. Hayward, I was impressed by the remarkable nature of its pleochroism. A day or so later, while examining some concentrates of the Blackheath Beds of Shirley, Surrey, belonging to Mr. G. M. Davies, I came across a single grain which he had described as glaucophane. The pleochroism seemed too intense for a grain of glaucophane of that thickness, and it occurred to me that the tint observed, when the grain was in the position of maximum absorption, was exactly that of the dumortierite grain.
On the determination of the optic axial angle and crystal-forms from observations by the Becke method in thin sections
Authors: Collingridge Harvey
Published: December 2006

Some years ago the writer read a paper on the determination of the optic axial angle of a crystal by the Becke method. This proposed method was to record the trace of the optic axial plane when horizontal, the position of one axis, and the extinction-direction. From these data and the established constants of the microscope, the position of the second optic axis may be found, as the extinction bisects the angle between the centre of the pole of the section and the two optic axes. Hence, the optic axial angle may be determined.

Considerable errors arise in these determinations owing to defects in the optical system of the microscope, and also to the inability to determine the exact position when the trace of the optic axial plane is parallel to the E-W. lines in the microscope.
A contribution to the petrology of the Whin Sill
Authors: Tomkeieff S. I.
Published: December 2006

The ‘Whin Sill’ of the north of England is a classic example of an igneous intrusive sheet. A detailed account of its general tectonic and petrographic features has been the subject of a recent; paper by A. Holmes and H. F. Harwood. The present author has made the attempt not so much to give a complete account of the petrology of the Whin Sill, as to describe certain peculiar developments within its mass, such as the coarse-grained bands, acid segregations, &e.
The variation of optical properties with chemical composition in the rhodonite-bustamite series
Authors: Hey Max H.
Published: December 2006

A specimen of hardystonite from Franklin Furnace, New Jersey, U.S.A., purchased in 1899 from Mr. W. M. Foote of Philadelphia for the British Museum collection consists largely of an associated pale pink mineral which has at various times been thought to be rhodonite, fowlerite, wollastonite, or scapolite. This specimen has recently again attracted attention because of the remarkable fluorescent effects it shows in ultra-violet rays. The pink mineral displays a bright brick-red fluorescence, the hardystonite a violet; and some willemite present fluoresces a brilliant green. A description in the literature of such a mineral from Franklin Furnace being unknown to Dr. L. J. Spencer, he handed over to me the problem for investigation, and a detailed examination has proved the pink mineral to be bustamite.
The occurrence of potassium nitrate near Goyder's Pass, McDonnell Ranges, Central Australia
Authors: Mawson Douolas
Published: December 2006

About two years ago an aboriginal at Alice Springs in Central Australia reported that at a spot near the western extremity of the McDonnell Ranges the earth, if thrown upon a camp fire, did not extinguish the flames, but on the contrary increased the blaze. To those who heard the story this suggested the occurrence of oil, and it was decided to make some investigations. With the assistance of the native the spot was visited and located on the map. A sample of a white substance, which stimulated the burning of faggots, was forwarded to Adelaide University for examination and proved to be potassium nitrate. As a consequence Mr. C. T. Madigan, B.E., M.A., and myself paid a visit of inspection to the locality.
A simple method of observing the magnetic properties of mineral grains
Authors: Smithson Frank
Published: December 2006

In examining mineral grains either from sands or from crushed rocks it is frequently found that the electromagnet not only affords a means of separating certain minerals, but is also an aid to their identification. Yet an electromagnetic separation is rarely, if ever, complete, and minerals are frequently found to stray into fractions to which they do not rightly belong. As a result, a grain which, let us say, is found in the garnet fraction may be practically nonmagnetic, and if we assume that its magnetic properties are similar to those of garnet, a misidentification may be made. It seems desirable, therefore, that there should be some means of testing the magnetic properties of a single grain.
On the orientation of kamacite in meteoric iron
Authors: Young James
Published: December 2006

The present note arises out of a paper by O. B. Bøggild, to which my attention was drawn recently, concerning the peculiar segregation of kamacite which gives rise to the Widmannstätten figures produced by etching plane sections of the octahedrite meteoric irons.

As the figures which occur in these meteorites are met with on a much smaller scale in many alloys, the structure to which they owe their origin must be of special interest to those engaged in the study of metals.
The dolerite-chalk contact of Scawt Hill, Co. Antrim. The production of basic alkali-rocks by the assimilation of limestone by basaltic magma (With Plates XVII and XVIII.)
Authors: Tilley C. E. , Harwood H. F.
Published: December 2006

In the following pages an account is given of the rock assemblages produced at the contact of a dolcrite intrusion with chalk. Owing to the intense localized assimilation of calcium carbonate by the dolerite magma, unusual rock types are produced. The products of the endogenous contact-zone are dealt with in detail. Those of the exogenous contact-zone have in part been described already, but some additional data are incorporated in this account.
Clouded felspars and thermal metamorphism
Authors: MacGregor A. G.
Published: December 2006

The present paper summarizes the facts at present known regarding a characteristic effect that is often produced in the fresh plagioclase felspars of igneous rocks by thermal metamorphism—namely the development of a special type of cloudiness caused by the appearance of minute inclusions. Reference is also made to certain wel|-known rocks in which the clouding of plagioclase felspars has been described without any suggestion that the peculiarity of the felspars is connected with thermal metamorphism.
The meteoric stone seen to fall in the Mangwendi native reserve, Southern Rhodesia, on March 7, 1934
Authors: Lightfoot B. , Macgregor A. M. , Golding E.
Published: December 2006

This is the first meteorite to be recorded from either Southern or Northern Rhodesia. It fell at about 12.45 p.m. on March 7, 1934, on the right bank of the Shawanoya river in the Mangwendi native reserve, about forty miles east of Salisbury. The latitude and longitude of the spot are 17° 39ʹ S., 31° 36ʹ E.

The recovery of the meteorite was made through the efforts of the Rev. F. J. Gits, S.J., who is in charge of St. Paul's Mission. Three loud detonations were heard from a direction north-east of the Mission Station followed by a loud rushing sound. Father Gits, who was out in the open at the time, involuntarily ducked his head. His inquiries failed at first to elucidate the cause of the explosions, which were also heard at Arcturus, Macheke, and Mtoko, that is, over a radius of at least fifty miles.
Murnpeowie (South Australia), a granular type of meteoric iron
Authors: Spencer L. J.
Published: December 2006

Apreliminary account of this fine mass, weighing 2520 lb., of meteoric iron was given in 1910 by L. Laybourne Smith, who at that time was Registrar of the South Australian School of Mines and Industries in Adelaide; but the promised detailed description with chemical analysis never appeared. Except for a small piece cut off one corner (upper left-hand corner in fig. 1) the mass is preserved intact in the Museum of that Institution, and none of the material appears to have been distributed to other museums. Casts of the mass were, however, made for the South Australian Museum in Adelaide, and one of them was presented to the British Museum in 1917 (B.M. 1917,360), where in the meteorite collection it is a very striking object (fig. 1).

Recently, at the suggestion of Mr. R. Bedford of the Kyancutta Museum, the Council of the South Australian School of Mines has generously presented to the British Museum a piece of this meteoric iron, together with the milling cuttings, with the request that the description of it should be completed.
The determination of small amounts of copper in rocks
Authors: Groves A. W.
Published: December 2006

In modern petrology increasing importance is being attached to the content of minor chemical constituents, the determination of which is now frequently required, whereas hitherto they have usually been disregarded. In consequence, methods for their accurate determination in small amount have not always been fully worked out. Copper is a case in point, and it is already clear that the method here advocated will show that this metal is much more widely distributed in rocks than is generally realized. Moreover, the use of a large sample, such as 20-50 grams, is no longer necessary.

In attempting to apply to rocks the very sensitive colorimetric method described by T. Callan and J. A. Russell Henderson, various difficulties were encountered, and modifications were developed whereby the method can be adapted to the determination of from 0·001-0·25 % of CuO in silicate rocks and minerals. The reagent used is sodium diethyl-dithio-carbamate, which gives a yellow colour with copper in slightly ammoniacal solution. The authors give a list of other metals which also give a coloration or turbidity with this reagent.
Metasomatism associated with the greenstone-hornfelses of Kenidjack and Botallack, Cornwall
Authors: Tilley C. E.
Published: December 2006

In a paper entitled 'Hornfelses from Kenidjack, Cornwall' 1 the nature and origin of the rock types characterized by anthophyllite and cummingtonite occurring in the aureole of the Land's End granite were discussed.

Since these rocks were 'investigated in 1928 the writer has extended his study of them both in the field and in the laboratory, with the result that further light on the origin of these rock types has been obtained. It is the purpose of these notes to examine in more detail the evidence which is considered to add to their understanding. In the Kenidiack paper the petrography of the rocks was described at some length and in the present paper petrographic data will be given only in so far as they supplement the previous account, which may be consulted for a detailed statement.
The late Palaeozoic quartz-dolerites and tholeiites of Scotland
Authors: Walker Frederick
Published: December 2006

Towards the close of the Carboniferous period in Britain, igneous activity, which had been prominent from time to time throughout the system, broke out afresh in a new form affecting a large area of the country between the Moray Firth and the River Tees. This activity was entirely, hypabyssal in character, the intrusions consisting of basic dikes and sills belonging without exception to the tholeiite magma-type of Dr. W. Q. Kennedy and W. Wahl. Those in the north of England include the famous Whin Sill and have been studied in great detail, particularly by Professor A. Holmes and by Dr. J. A. Smythe. The same cannot be said of their Scottish representatives. They possess, indeed, an abundant literature and several excellent publications deal with the intrusions of limited areas, but there is no connected account of them as a whole. Many districts, in fact, appear to have escaped investigation almost completely.
The effects of heat on the optical orientation of plagioclase felspars
Authors: Barber C. T.
Published: December 2006

Aconspicuous feature of all published diagrams, showing the results of the determination of a number of plagioclase felspars by the Fedorov method, is the pronounced scattering of the poles. They lie not only on the curves of the determinative stereogram, but on either side of them, and, in fact, occupy a belt, varying in different instances, and in different positions along the length of the same curve, from 3 to 8 mm. in width. These belts usually contain, but are not symmetrically disposed to, the curves.
Demonstrations in petrogenesis from Kiloran Bay, Colonsay
Authors: Reynolds Doris L.
Published: December 2006

In 1911 Dr. W. B. Wright briefly described the felspathized quartzite blocks in the hornblendite of Port Easdale, Kiloran Bay, Colonsay, Hebrides. He showed that the exposures provide a conclusive demonstration that the action of hornblendite magma on quartzite xenoliths was to convert them to alkali-felspar and quartz, so that in the final stage ‘one can recognize in numerous angular and rounded patches of felspathic material, without visible xenolithic core, the ghosts of former masses of quartzite’.
The Tenham (Queensland) meteoritic shower of 1879 (With Plates XIV-XVII.)
Authors: Spencer L. J.
Published: December 2006

Very little reformation can now be gathered about a remarkable shower of meteoric stones that fell many years ago in a remote district in south-west Queensland. Only a few scraps of information have appeared in print, and these are largely contradictory. However, some very tangible evidence arrived unexpectedly at the British Museum in 1935 in the form of a remarkable collection of 102 complete meteoric stones with a total weight of 107¾lb. This material had been in the possession of Mr. Benjamin Dunstan, formerly Government Geologist of Queensland, who had been collecting information of the fall with a view to writing up an account for publication. This unfortunately he never did, and much of the information is now lost. The specimens were offered to the British Museum by his widow, but they came along quite casually as an appendix to a collection of fossils.
X-ray studies on pyrolusite (including polianite) and psilomelane
Authors: Vaux George
Published: December 2006

One of the most promising uses of X-ray diffraction methods in mineralogy is the study of those minerals which are opaque and whose crystals are extremely minute. Although recent methods of ore examination by reflected polarized light have given valuable information about these substances, their application to soft, powdery materials is extremely difficult, an objection which does not apply to X-ray methods.

Pyrolusite (including polianite).—The present study had for its main objective an attempt to settle, by X-ray examination , the uncertainty existing as to the relationship between polianite and pyrolusite, Work already carried out by St. Johns has suggested that polianite and pyrolusite are identical, since they have the same cell sides as found from powder photographs.
The Paragenesis of Kyanite-amphibolites (With Plate XX.)
Authors: Tilley C. E. , Vincent H. C. G.
Published: December 2006

In an earlier paper the writer has discussed the paragenesis - kyanite-omphacite as observed in certain ec|ogites. The fate of this association under conditions of retrograde metamorphism has led to a consideration of rocks showing the paragenesis amphibole-kyanite, a point which is briefly taken up in the present communication. Rocks containing this latter assemblage include two groups, the one better known, of sedimentary origin, the other essentially igneous in origin.

Here are included members of the para-amphibolites, biotite-hornblende- schists, and hornblende-Garbenschiefer derived from sediments of the character of calcareous and dolomitic shales. The best-known examples come from the Alps—particularly the Triassic and pre- Triassic sediments on the south side of the St. Gotthard massif.
On scawtite pseudomorphs after spurrite at Scawt Hill, Co. Antrim
Authors: Tilley C. E.
Published: December 2006

Scawtite was first described at Scawt Hill as a secondary mineral occurring in vesicles and venules in melilite of a melilite-rich hybrid of the endogenous contact-zone. Since then scawtite has been identified in a gehlenite-vesuvianite-ealcite-rock from the contact-zone of a gabbro in the Little Belt Mountains, Montana. The present note records a further occurrence of scawtite at Scawt Hill in a different patagenesis, viz. in association with and replacing spurrite of the exogenous contact-zone.
The stilpnomelane group of minerals
Authors: Hutton C. Osborne
Published: December 2006

Work which has been in progress during the last few years on the low-grade regionally metamorphosed rocks of western Otago, New Zealand, has shown that members of the stilpnomelane group, hydrous iron- (or manganese-) rich silicates, are exceedingly widespread in rocks with the most varied mineral assemblages. In many cases the mineral in question is in sufficient quantity to rank as an essential constituent and may even be the most abundant one present. Hence in view of the importance of this mineral in the rocks of this region, it was considered that exact analytical data were necessary, and preliminary work in this connexion was carried out by Dr. F. J. Turner and the writer in 1934, but at that time, owing to the difficulties of separation, the pure minerals could not be obtained for analysis.
An X-ray examination of some potash-soda-felspars
Authors: Chao S. H. , Smare D. L. , Taylor W. H.
Published: December 2006

The systematic classification of the potash-soda-felspars is of the greatest interest and importance to the mineralogist, but problems demanding physical investigation are raised in work carried out recently by Dr. Edmondson Spencer, who has described the results of exhaustive chemical, optical, and thermal investigations of a representative collection of these minerals. Dr. Spencer has very kindly allowed us to examine by X-ray methods a large number of his specimens, so that for the first time it has been possible to make a fairly complete survey of potash-soda-felspars of known chemical composition and with accurately measured optical properties.

This paper presents the results of our general survey of potash-soda-felspars with compositions ranging from nearly pure potash-felspar to approximately 50 % soda-felspar. The natural minerals, and the same minerals after specified heat-treatment, have been examined. We do not discuss in detail the interpretation of our results in terms of the atomic structure of felspars; the subject is extremely complicated, and it is necessary to await the results of other investigations now in progress in this laboratory before attempting a complete structural interpretation.
Note on a specimen of white beryl from Beam mine, St. Austell, Cornwall
Authors: Hallimond A. F.
Published: December 2006

The specimen, which is in two pieces cemented together, was purchased for the Museum of Practical Geology in February, 1888, from Mr. F. H. Butler, and bears the Museum's original Mineral Inventory label (M.I. 5714) on each portion. The inventory description is “Tin-stone, well crystallised, coating granite, Beam mine, Cornwall”. The exhibition label mentions quartz, and the presence of beryl had no doubt been overlooked through the general resemblance to milky quartz, which is not uncommon on some Beam mine material. Actually it was noticed during the rearrangement of the collection in 1934 that the cassiterite is accompanied by large, dull white crystals which proved to be beryl. In view of the rarity of beryl in Cornwall a brief description may be of interest.
The composition of francolite
Authors: Sandell E. B. , Hey M. H. , McConnell Duncan
Published: December 2006

In 1850, T. H. Henry published an imperfect analysis of francolite, a supposed new mineral, previously named by H. J. Brooke. Henry stated that his material was similar to the material from Wheal Franco, Tavistock, Devon, but he does not show how he was in a position to know the composition of the material from this mine, because there is no record to indicate that the mineral from Wheal Franco had been analysed. Henry did not report CO2 for the material he analysed, but M. H. N. Story-Maskelyne and W. Flight analysed material, supposedly similar, and obtained a significant amount of CO2.
The structure of orthoclase
Authors: Chao S. H , Hargreaves A. , Taylor W. H.
Published: December 2006

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.
Note on an occurrence of bertrandite and beryl at the South Crofty mine, Cornwall (With Plate XXV.)
Authors: Phemister James
Published: December 2006

Among a series of specimens collected by Mr. H. G. Dines from the South Crofty mine, Illogan, one was found to contain bertrandite and beryl. The specimen was obtained from the back of the 290-fathom level, east of Robinson's shaft, in the no. 1 lode, which hades north and at this position is 3 feet 10 inches wide. The location of the specimen was about 9 inches from the granite footwall. In hand-specimen the rock is a normal stanniferous veinstone composed of massive quartz tinted grey-green by disseminated chlorite and tourmaline and traversed by stripes of blackish ‘peach’ and white vein quartz which run parallel to the lode walls. Microscopically it is composed essentially of quartz, chlorite, and tourmaline, with subordinate orthoclase, fluorspar, and cassiterite, accessory apatite, and local bertrandite and beryl. In its texture there is evidence of an early formation of stanniferous chlorite-tourmaline peach with quartz-fluorspar gangue, which was subsequently fractured and, later, more or less completely healed by an accession of quartz, some redistribution of the earlier minerals having taken place at the same time. The place of bertrandite and beryl in this general scheme is discussed below (p. 576).
On sulphatic cancrinite and analcime (eudnophite) from Loch Borolan, Assynt
Authors: Stewart F. H.
Published: December 2006

The minerals to be described in this paper were collected, in conjunction with W. E. Fraser, who was carrying out a detailed study of the borolanite, from the road-metal quarry, opened in 1938, at Allt a' Mhuillin, Loch Borolan, Assynt, Scotland. They occur in pegmatitic patches and veins in borolanite.

This mineral is one of the chief constituents of the pegmatites. It forms large cleavable masses, associated with orthoclase, melanite, and a little dark mica. Calcite, sphene, zircon, and orthite are present as accessories. It often fills interstices between crystals of orthoclase. A preliminary examination has indicated that it is a common constituent of the spots in some types of borolanite, and further work will have to be done to determine its importance in this connexion. This is the first definite record of the occurrence of cancrinite in Britain.
The Gibeon shower of meteoritic irons in South-West Africa (With Plates I and II)
Authors: Spencer L. J.
Published: December 2006

The presence of much native iron in Great Namaqualand was heard of in 1836 by the traveller Sir James E. Alexander, but he himself did not see any of the masses, and the material he acquired consisted only of small fragments that had been detached by the natives for pointing their weapons. An approximate chemical analysis of this material, made by Sir John Herschel, proved it to be meteoritic. A fragment weighing 2 grams which Alexander presented to the Geological Society of London in 1838 was transferred to the British Museum collection of meteorites in 1911. This appears to be all of his material that has been preserved.

Various other vague reports and travellers' tales have mentioned the presence of large masses of iron beyond the old mission station of Bethany, between there and Beersheba, and on the east side of the Great Fish River. A critical summary of these accounts was given by Sir Lazarus Fletcher in this magazine.
Some new data concerning kornerupine and its chemistry
Authors: Hey Max H. , Anderson B. W. , Payne C. J.
Published: December 2006

Some years ago, when working through large parcels of mixed faceted gem-stones in a search for blue spinels of high refractive index, several unusual specimens were encountered, two of which were later identified as kornerupine by Dr. G. F. Claringbull, using X-ray methods. The other stones in these parcels were all quite typical products of the Ceylon gem gravels, consisting mainly of zircons, garnets, and spinels. Since kornerupine is so rare a mineral, and had not previously been reported from Ceylon, it was considered worth while to attempt to place the new occurrence beyond doubt by searching through rough gem gravel imported direct from Ceylon. This was made possible by the kindness of Mr. Hans Van Starrex, who sent a consignment weighing several pounds from the Matale district (Anderson and Payne, 1940).
The orientation of Widmanstetter figures in a random section
Authors: Melmore Sidney
Published: December 2006

The problem of determining the orientation of Widmanstetter figures has recently arisen in a paper by Dr. L. J. Spencer on the Gibeon shower of meteoritic irons in South-West Africa: the method of attacking it to be described here will be applied to the crystals illustrated in plate II of his paper.

By producing the faces of a regular octahedron in all possible directions a set of six congruent prisms is formed, as shown in fig. 1. The Widmanstetter figures are the traces of these prisms in a plane of section. The section across any one of the prisms by a plane normal to its axis is a rhomb whose angles are those of a face of the rhombic-dodecahedron, that is to say, 70° 31′ and 109° 28′.
On the origin of the name ‘quartz’
Authors: Tomkeieff S. I.
Published: December 2006

Quartz is the commonest of minerals and reference to any dictionary will show that it is crystalline silica, but how or when this substance acquired the name quartz seems to be a still unsolved mystery.

Theophrastus, the pupil and successor of Aristotle, in his book on stones (19), mentions among other stones used for engraving seals, a stone called crystal This name, apparently, is derived from cold, and contract. It would seem from this that the ancient Greeks, as implied by Pliny, believed crystal (modern quartz) to be a variety of supercooled ice. In point of fact the formation of crystal in nature is explained by the earliest writers in a different way. Diodorus Siculus (circa 30 B.C.) suggests that crystal was formed from water hardened by heavenly fire, while Pliny the Elder (circa A.D. 60) says that crystal is ‘a substance which assumes a concrete form from excessive congelation’, and goes on to explain that crystal is only to be found ‘in places where the winter snow freezes with the greatest intensity’ (15, Book 37, 2, 9). Pliny's description of crystal, however, leaves no doubt that he applied this name to the crystalline variety of silica which is now called quartz.
An analysis of the movements of shadow-edges on the refractometer in the case of biaxial gemstones
Authors: Burbage E. J. , Anderson B. W.
Published: December 2006

The study and identification of the gem minerals present difficulties which are not to be resolved by the ordinary methods of mineralogy. The commercial value of the material forbids recourse to chemical reagents and the blowpipe, and when faceted and mounted, the criteria of crystal form and specific gravity are also inapplicable. Optical phenomena then constitute the sole means of discrimination, and the refractometer, spectroscope, polariscope, and dichroscope become the only arbiters between gemstones of similar appearance but different species. The function of the polariscope is to narrow the field of inquiry by differentiating between isotropic and anisotropic gemstones; the verdict of the spectroscope is unequivocal in gemstones characterized by absorption spectra, which, unfortunately, form a minority ; dichroism, when present, can be regarded as supplementary evidence only; the refractometer, an instrument of wider application than the spectroscope, and capable of yielding information which is usually equally unambiguous, thus assumes a role of primary importance.
Cummingtonite and gedrite from Sutherland
Authors: Collins R. S.
Published: December 2006

During the investigation of a migmatite complex near Strathy, north Sutherland, cummingtonite and gedrite were found to be common constituents of certain schists and granulites. Calcium-poor amphiboles have not hitherto been recorded from rocks of the Moine Series, and it is the purpose of this paper to give the results of the optical and chemical study of three examples of this group. The methods of separation and purification employed are described in some detail as it is considered that many of the previous analyses of these minerals are vitiated by faulty procedure. To avoid errors in separating two amphibole species, the investigated samples were taken from rocks containing a single amphibole phase. The paper concludes with a discussion of the correlation of optical properties and chemical composition of cummingtonites and gedrites.
Brammallite (sodium-illite), a new mineral from Llandebie, South Wales
Authors: Bannister F. A.
Published: December 2006

During a study of the petrography and mineral constituents separated from various shales overlying the coal-measures of South Wales, Dr. Alfred Brammall noticed on several hand-specimens from Llandebie a white infilling to fissures or a coating on slickensided surfaces which could be readily detached from the matrix. Chemical examination showed that this coating, unlike the shales themselves, contained more sodium than potassium. The present note gives an account of subsequent chemical, X-ray, and optical work, which confirms Dr. Brammall's suggestion that the white incrustation contains a new sodium-rich mineral allied to mica. It is not, I hope, an unfitting tribute to his work in this field as well as to his interest in recent advances in mineralogy that I have named this mineral brammallite. A short account of its nature and relationship to illite, which is the chief constituent of the shale itself (see preceding paper, p. 297), will now be given.
Notes on the cleaving and sawing of diamond
Authors: Grodzinski Paul
Published: December 2006

It seems to be a peculiarity in the history of the diamond that from time to time operations which have been known from time immemorial are re-invented and claimed to be new. For instance, cleaving, which is said to have been known to the Indians, was discovered again by W. H. Wollaston. It is obvious, too, that cleaving was already known to A. B. de Boodt in 1604. The same applies to the sawing of gems by a thin rotating disk, which seems to be as old as the engraver's treadle lathe (earliest reference about 1520) ; but this art does not seem to have been applied to diamonds, as the first reference to diamond sawing with a thin rotating blade is that in 1874. All previous references seem to be to the sawing of diamonds with a thin wire moistened with a paste of diamond dust and oil, and otherwise designated as the Chinese method. Other gemstones, were always sawn with thin disks on lapidaries' benches with vertical spindle. Similar remarks may be applied to bruting and drilling, but only polishing seems to have always been recognized as the main operation.
An X-ray study of the crystal-structure of antigorite (With Plate V)
Authors: Aruja Endel
Published: December 2006

Antigorite is a lamellar variety of serpentine, and is supposed to be a dimorphous form of chrysotile, which is finely fibrous. Its chemical composition is approximately H4Mg3Si2O9, which is taken as the basis of calculations here.

This study was undertaken primarily because it was hoped that knowledge of the structure of antigorite would throw some light on that of chrysotile. Certain similarities between the two structures have been established, namely in the c(7·3kX or 14·6kX), and b(9·2kX) directions. There are two main differences, however. Firstly, imperfections which cause line broadening in the X-ray pattern of chrysotile, are absent in antigorite (apart from certain ‘streaks’). Secondly, the a(43·4kX) axis of antigorite is approximately eight times longer than the corresponding axis in chrysotile. A complete determination of the structure has not been achieved, but the X-ray pattern has been described, and some suggestions made as to the explanation of the peculiarities observed. A further study of the outstanding questions is in progress.
Myrmekite in graphic granite and in vein perthite
Authors: Spencer Edmondson
Published: December 2006

This paper describes the occurrence of myrmekite in a graphic quartz-microcline-rock from the mica-bearing pegmatites of Kodarma, Bihar, India. The myrmekite has grown out from the quartz-mierocline junctions into the potash-felspar with the appearance of having replaced the latter. The two are in optical and crystallographic continuity and, owing to the large ‘single crystal’ character of the microcline, definitely oriented sections can readily be prepared. A detailed study of these sections shows that the myrmekite has been formed by the segregation and coalescence of microperthitic albite formerly held in solid solution in the potash-felspar. Successive stages in this process of segregation can be observed.

These sections also provide evidence of the paragenetic relationship between the quartz rods, the vein perthite, and the body microcline. This is supplemented by additional evidence from graphic granites and vein perthites obtained from other localities.
An account of the struy lead mines, Inverness-shire, and of wulfenite, harmotome, and other minerals which occur there
Authors: Russell Arthur
Published: December 2006

The Struy lead mines (Six-inch ordnance Survey, Inverness-shire, sheet 17) are situated on the west side of Strath Glass, about two miles south-west of Struy village, and comprise three distinct sets of small long-abandoned workings, two of them being in the nature of trials only. All three workings are shown on the six-inch map, and are on veins traversing the Moine schists. The Geological Survey Memoir of the district says that four veins may be traced on the hill face between the Dùn south of Struy school and Crelevan; if this is correct there are two outcrops I have not seen. The mines are on what was until a few years ago part of Lord Lovat's estate. The date of their discovery is not known, but they were apparently worked about the year 1818 by Thomas Alexander Fraser (afterwards 12th Lord Lovat) at the same time as his graphite mine in Strath Farrar; most of the work seems, however, to have been done by him between 1838 and 1845, when miners were brought from England and housed in cottages specially built for them in Struy village. In 1864 the Loch na Mèine workings were cleared and prospected, but since then no further work has been done.
Simpsonite and other tantalates from Bikita, Southern Rhodesia
Authors: McGregor A. M.
Published: December 2006

The Bikita tin and tantalum field is centred about 43 miles east-north-east of Fort Victoria, in the south-eastern part of Southern Rhodesia. It forms the end of a tongue of basic and sedimentary schists surrounded on three sides by granite. Tin and tantalum minerals have been known in the area for over thirty years, and at various times attempts to work them have been made, but with indifferent success. During recent years the demand for tantalum has led to the re-opening of the field and several tons of tantalite and simpsonite concentrates have been exported to America. The area was mapped geologically by Mr. R. Tyndale-Biseoe in 1942, but the publication of the map and report have been held up during the war. The principal workings are the Mdara mine and the Al Hayat claims situated about three-quarters of a mile apart.
Barium-felspars from Broken Hill, New South Wales (With Plate XIV.)
Authors: Segnit E. R.
Published: December 2006

At two localities on the outskirts of the township of Broken Hill—near the De Bavay shear zone, and at ‘The Piggery’—W. R. Browne reported unusual rock types rich in barium. His statement is accompanied by an analysis by H. P. White (analyst to the Mines Dept.) of one of these rocks, which contains 9·23% BaO. Subsequently S. R. Nockolds and E. G. Zies examined the felspars of the rock analysed by White with a view to ascertaining whether they are barium-containing varieties.

In view of the very high barium content of some of the occurrences now being investigated, much higher than that of the rock examined by Nockolds and Zies, a further mineralogical investigation was undertaken with the results recorded below. The rocks under examination were light-coloured gneisses containing up to 15% BaO. They are distributed as lenses and streaks in an acid gneiss. A specimen of the latter rock was analysed and found to contain only 0·09% BaO. The barium was found to occur in four felspars, one being a new variety of celsian. The minerals studied were celsian, calciocelsian, hyalophane, and barium-plagioclase. A careful search was made for other barium silicate minerals such as sanbornite, but none was found.
Pennantite, a new manganese-rich chlorite from Benallt mine, Rhiw, Carnarvonshire
Authors: Campbell Smith W. , Bannister F. A. , Hey Max H.
Published: December 2006

The manganese ores of the Benallt mine are pervaded by an orange-coloured mineral which occurs very poorly crystallized as patches and small specks in the matrix. Less commonly it occurs as minute flakes in the ore and sometimes as a constituent of very thin veins which traverse the ore. In some specimens the mineral is better developed. It then shows a good cleavage and resembles in appearance in thin section a weakly pleochroic mica or chlorite. Patches of this mineral in the matrix frequently enclose very small rounded garnets which are believed to be spessartine.

In 1932 Dr. A. F. Hallimond examined some sections of ore from the old Benallt mine for Dr. C. A. Matley and suggested that one of the constituent minerals might be a manganiferous chlorite.
Bustamite from Treburland manganese mine, Cornwall, and its paragenesis. (With Plate XV)
Authors: Tilley C. E.
Published: December 2006

Bustamite forms an important constituent of the manganese ores of the Treburland mine near Altarnun, Cornwall. The rediscovery of this mineral locality is due to Sir Arthur Russell, who has already presented an account of the rhodonite and tephroite of the mine (Proc. Min. Soc. 1944, p. xix). Since then the writer has noted bustamite and bementite from the same locality (ibid. 1944, p. xxvi), and it is the purpose of the present paper to discuss the composition and paragenesis of this bustamite.

Rhodonite and tephroite form the chief silicate constituents of the manganese ores exposed On the dumps adjacent to the old Treburland mine shaft, but bustamite-bearing assemblages are not uncommon.
A contribution to the study of luxullianite
Authors: Wells Maurice Kingsley
Published: December 2006

Lxullianite is well known, at least by name, in this country, and indeed it enjoys an international reputation among petrologists. Its general characters have been described by Bonney and Sir John Flett, while reference to the type is to be found in most standard text-books on petrology. It is, however, a rock of outstanding interest and deserves fuller description and illustration than have yet been accorded it.

The preparation by Mr. A. V. Weatherhead of a large set of thin sections for teaching purposes has given the writer an opportunity of making a more detailed examination of the micropetrology of the rock, with special reference to the manner of the replacement of the several original components.
Variation in the structure of zircon
Authors: Stott Vaughan H. , Hilliard Alfred
Published: December 2006

In the course of an investigation on refractory materials, in which the identification of minerals by their X-ray diffraction patterns had a prominent place, an interesting observation was made on a zircon of gem quality which was lent to us by the courtesy of Mr. B. W. Anderson.

It may be recalled that the existence of three allotropes has been postulated in order to explain the considerable variations of physical properties which are found when comparing different specimens of zircon. In particular, densities ranging from 3·95 to 4·86 have been observed, the density of zirconium silicate, calculated from X-ray measurements, being 4·71.