MINERALOGY

during the war period of 1914-8 much attention was given in all countries to the development of home resources of various minerals of economic value, and to meet new circumstances new sources of supply were developed. further, there was an increased demand for certain kinds of minerals, for example those which yield the rarer metals used in the hardening of steel. much of the mineralogical literature of the period was therefore of an economic character, and many recent text-books gave prominence to the practical uses of min- 923 erals. fortunately, however, pure science was not altogether neglected. many new facts have been recorded, and new meth- ods of investigation have been devised. x-ray examination of minerals —the x-ray method of in- vestigating the internal structure of crystals has been applied with much success to the study of minerals (see crystallog- raphy). the material for examination has usually been prepared as definitely orientated crystal plates, but it is found that the results can be obtained with a fine powder, 7.¢., an aggregate of minute crystals or fragments of crystals with all possible orienta- tions. the method can therefore be used for the purpose of dis- tinguishing between the crystalline and the amorphous or col- loidal states. since each crystallised mineral gives a more ‘or less characteristic series of bands on the photographic film, the powder method may also be used for the recognition of the min- erals present in intimate mixtures, such as fine-grained rocks, ores, clays and soils. x-rays have also been employed in a method of spectrum- analysis for detecting the presence of the various chemical cic- ments present in minerals. for example, hafnium has been detected, and the amount approximately estimated, in many zirconium minerals. microscopical fxamination of opaque minerals —a method for the investigation of opaque mincrals borrowed from metal- lography (g.v.), in which polished sections are examined uncer the microscope in rellected light, has proved to be especially uscful for the study of metallic ores. it consequently finds an economic application in the valuation of ore deposits. the several mineral species of which the ore is composed can be dis- tinguished, and their relations to one another determined; c.g., the order of their deposition, and whether they are of primary or secondary origin.! the process of grinding and polishing the sections presents certain difficulties owing to the extreme differences of hardness of the several minerals that may be present. the prepared section is illuminated vertically by means of a right-angle prism placed in the tube of the microscope above the objective. details of structure can be brought out by etching the section with various chemical reagents. the several characters (colour, hardness, relief) of the minerals, together with their behaviour towards reagents, help in their determination. but in many cases ordinary simple tests made on fragments detached from the polished surface are more reliable, eiectrical tests can be mide with quite simple apparatus: for example, the electrical con- ductivity can be determined with a dry cell and voltmeter using needles as terminals on the polished surface. certain optical deter- minations can also be made in reilected polarized light. one result of this study of opaque minerals is to draw attention to the extremely intimate association and intergrowth of many of the ore-minerals; this is well shown in the numerous photo-niucrographs published hy american workers in economic geology. what to all appearances by ordinary methods is a homogeneous mineral may be found by the new method to be really heterogeneous; and, in fact, several supposed mincral species have been proved to be mixtures, and well-developed crystals have in certain cases been found to contain enclosures of other minerals. the method is thus of use for ascertaining the degree of purity of material collected for exact chemical analysis when the formula of a species is to be established. the long-debated question as to how silver exists in argentiferous calena (lead-ore) has been studied by this method. galena contain- ing 0-10 to 0:35° 5 of silver shows definite spots of tetrahedrite and argentite, whilst specimens containing more silver show evidence of later addition of proustite or pyrargyrite in the form of veinlets, mineral transformations.—in synthetical mineralogy a large amount of experimental work has been done, especially in the geophysical laboratory of the carnegie institution at washing- ton. many minerals and allied compounds have been prepared artificially in silicate and salt fusions. the conditions necessary for their formation and their ranges of stability—either when alone or when in the presence of other compounds—have been studied in detail. one important result obtained by experiment- ing over wide ranges of temperature has been to show that prac- tically all compounds known as minerals exist in several poly- morphous forms. 1 the technique of the subject (called mineralography or minera- graphy) is dealt with in the text-books: j. murdoch, aficroscopical determination of opague minerals (new york, 1916) and w. m. davy and c, m. farnham, jffcrescepic examination of the ore aflix- erals (new york, 1920.) 924 the work has shown that silica (sio.) undergoes a remarkable series of changes in its crystalline structure and physical characters when it is submitted to different degrees of temperature. the changes with increasing temperature are:— sndies: a-quartz (rhombohedral trapezohedral), passing at 575, c€. into 8-quartz (hexagonal trapezohedral), passing at 870 c. into a-tridymite (hexagonal holohedral), passing at 1,470°c. into b-cristobalite (cubic) melting at 1,625°c. these transformations are reversible, but with falling temperature they take place very slowly. molten silica unless cooled very slowly solidifies as a glass. 8-tridymite when quickly cooled undergoes 2 change at 163° c. (8.-tridymite to b,-tridymite), and at 117° c. passes over into a-tridymite, which is optically biaxial and probably orthor- hombic in crystallisation, being identical with the naturally occurring tridymite. similarly, b-cristobalite when quickly cooled changes at about 180°-270° c. into a-cristobalite, which is optically biaxial (pseudo-cubic) and identical with the cristobalite occasionally found in voleanic rocks. | now these and many other similar changes give information as to the conditions of temperature under which various minerals were formed in nature, thus providing a “ geological thermometer.” for example, the presence of tridymite, or of pseudomorphs of the more stable quartz after tridymite, establishes that the rock in which they occur must have been formed at a tempcrature between 870° and t,470°c. the quartz of certain veins and that of granite present differences in structure which indicate that the former was formed below 575°c. and the latter above this temperature. or again, the presence of orthorhombic copper-glance (6-cuss) as a pseudomorph after cubic a-cu.s proves that the ore-deposit in which it occurs was formed at a tempcrature higher than 91°c. chemical composition.—the chemical composition of many minerals is still imperfectly understood, and even for some quite common species there are doubts as to the correct empirical formulae, especially as to the silicates, a satisfactory classifica- tion of which ts still wanting. many attempts have within recent years been made to gain some idea as to the constitution of the silicates; there has been much experimental work and plenty of speculation, but with no very clefinite results. in certain groups, ¢.g., the feldspars and the garnets, the composition can be satisfactorily expressed on the assumption of the iso- morphous mixing of different chemical molecules. but attempts to extend this principle to all silicates often lead to highly complex hypothetical molecules, the existence of which can only be regarded as doubtful. alternative suggestions have been put forward, such as the “ mass effect” of large molecules and the “ solid solution’ of certain other substances in the main mass of the crystal. experiments with silicate fusions show that vari- ous substances can be taken up, or dissolved, in certain amounts, giving on solidification apparently homogencous crvstals. radioactivity.—the strong radioactivity (q.v.) of uranium min- erals affords a ready means of recognising these valuable ores in the search for them by prospectors. the mineral may be wrapped up with a photographic plate, which is afterwards developed; but a simpler and quicker test is that with a quite simple (home- made) gold-leaf electroscope. a piece of the mineral to be tested is placed on the cap of the electroscope, which is then charged with electricity, readily developed by rubbing with glass or vul- canite (say the mouthpiece of a tobacco-pipe): if the mineral contains uranium (and consequently radium), the gold leaves will soon come together. it is always well to make a comparative test, timing the rate of collapse, with a picce of ordinary stone. determinations of the ratio of the amount of uranium to the amounts of the various products of its decay (radium, helium, lead, etc.) present in various radioactive minerals give (knowing the rate of the decay) some idea of the period of time during which these products have been accumulating. in this way esti- mates have been made of the age in years of these minerals and even of the age of the earth; but, of course, many unknown fac- tors must have been omitted from such caleujations. lead of radioactive origin, or isotropic learl—the final product of urani- um decay—is found to vary slightly in its atomic weight (¢.v.) according to the uranium mineral from which it is extracted. to radioactivity is ascribed the well-known “ pleochroic haloes ’’—tinv spots or borders of deeper colour surrounding microscopic inclusions—long ago observed in certain rock- forming minerals (cordicrite, andalusite, mica, etc.) when micro- sections of rock are examined in polarised light. the long and mineralogy continued emission of x-rays from zircon or other mineral grains has caused a change in colour of the surrounding mineral for distances varying from 0-002 to o-4 millimetre. a study of these has again given some information as to the age of the minerals. jn this connection it may be mentioned that much experimental work on the coloration of minerals has been done within recent years by exposing the minerals to the action of radiations of various kinds, including ultra-violet rays, cathode rays, x-rays and the rays emitted by radium salts. for example, some dia- monds acquire a green colour and fluorspar becomes blue when placed in contact with radium bromide. some new minerals.—iin descriptive mineralogy a con- siderable number of new minerals have been named, but unfor- tunately in many cases not completely determined and described. a few of the more prominent and well-established of these are: — carnotite,—hydrated vanadate of uranium and_ potassium, kl0-2u03-v.05-7 11.0, occurring as a canary-yellow crystalline pow- der impregnating sandstones over a wide area in western colorado and the adjoining portions of utah and new mexico. {n colorado it has been collected on a large scale for the extraction of vanadium, uranium and radium. it has also been found in south australia and in pennsylvania; and an allied mineral (tyuyamunite, containing calcium in place of potassium) is known from tyuya-muyun in russian turkestan. germanite.—a_ sulphide ore mineral containing copper, iron and the rare elements germanium (5-8°%,) and gallium (4-2%,). asa massive, reddish-grey mineral intermixed with tennantite it is found in some quantity at vsumeb in south west africa. kasolite.-—a hydrated silicate of uranium and lead, pbo-uo4-sios- h,o, forming radiating groups of small, ochre-yellow, monoclinic crystals. together with several other new but imperfectly defined minerals, it occurs as an alteration product of pitchblend at kasolo in katanga, belgian congo. lorandite.—sulpharsenite of thallium, tlasss, forming transpar- ent, monoclinic crystals with a carmine-red colour and adamantine lustre. it is found with realgar at allchar in macedonia, and is one of the few minerals that contain the rare clement thallium as an essential constituent (ti 59-5 %). muffite—recent experiments have shown that the only alumin- ium silicate that can be prepared artificially is the compound 3al04-2si0n, and not also3-siq.=allsio; (fibrolite) as formerly supposed. the same compound, as minute orthorhombic crystals, has been fount in slates fused by igncous rocks in the island of m ull, scotland, and has been named mullite. patronite,—vanadium sulphide, vsa, forming dark greenish-black compact masses. it occurs abundantly at minasragra, cerro de pasco, peru, where it is a valuable ore of vanadium. jt weathers very readily with the production of various highly coloured vanadium compounds; even on material kept in collections there is a slow growth of blue and green efflorescences. spencerite.— hydrated basic zinc phosphate, zn3(po.)2-zn(oh)o- 3i1.0, forming pearly white, scaly cleavage masses and small mono- clinic crystals. jt has been found in some abundance forming large stalactites in a cavern near salmo, british columbia. farbuitiie.—basic zinc phosphate, zn2({pos)>-zn{(oh)s, forming colourless, or faintly coloured green or red, anorthic crystals, with a perfect cleavage in one direction. it has been found in considerable quantity at the rhodesia broken hill mine in northern rhodesia. phortveitite.—silicate of scandium, yttrium, ete., (se, ¥)205-2si09, occurring as large orthorhombic crystals of prismatic habit in pegmatite in southern nerway and madagascar. this is the only mineral known to contain the rare element scandium in large amount, — bibltograpiy.— details of descriptive mincralogy are collected in appendices 1-3 of dana’s systent of mineralogy (new york, 1899- 1915); and numerical data respecting the constants of miucrals are tabulated in the international tables annuelles de constantes et dounees numerigues, & vol. (paris, 1912 etc.). a work of compre- hensive character is c, doelter, handbuch der mineralchemie, 4 vol. (dresden and leipzig, 1912 etc.). an advanced textbook on new lines 13 p. niggli, lehrbuch der mineralogie (berlin, 1924, with two more volumes to follow), a number of clementary textbooks have been published, e.g... g. a. j. cole, oudlines of mineralogy for geolog- tcal students (london, 1912); a. f. rogers, introduction to the study ef minerals (new york, tgt2): e. il. kraus and w. f. ifunt, mineratogy, an introduction to the study of minerals and crystals (new york, 1920); h. buttgenbach, les mineranx et les reches (paris and liege, 1924). a popular book with coloured platesis l. j, spencer, the world's afinerals (london, 1911, 2nd ed., new york, 1916), rooks of aa economic character are ul. ries, kconomic geology (5th ed., new york, 1928):"y. crook, econontic w tneralogy, a@ practical guide to the study of useful minerals (london, 1921); b. dammer and o. tictze, die nutsharen mineralien (2 val., stutt- gart, 1913-4). special reports an the mineral resources of great britain have been issued by the ( sxcological survey, london, since miners’ phthisis—mining 1915; and a long series of pamphlets, the mineral industry of the british empire and foreign ceuntries by the imperial mineral ke- sources bureau, london, since 1920. new journals are fortschriite der mineralogie, kristallographie und petrographie, issued by the (serman mineralogical society, jena, since 1981; beitrdge sur kristullographie und mineralogie, ed. by v. goldschmidt (ileidel- berg, since 1914); schwetserische mineralogische und petrographische mittetlungen, zlirich, since 1921. a review of the recent scientific literature is given in the mineralogical society's series of afiner- alogical abstracts. chee} 3e) miners’ phthisis (sce 18.541b).—almost any dust inhaled in sufficient quantity may cause chest trouble of some kind or another, but certain dusts are related to the occupational disease variously known as miners’ phthisis, pneumonokoniosis, grinders’ rot, potters’ rot, stonecutters’ rot, etc. phihisis-producing dusts—dusts with this association are often referred to as phthisis-producing dusts because pulmonary tuberculosis plays a more or less important part in this disease and is always associated with a fatal termination and usually with disablement. prof. e. l. collis has shown that the phthisis- producing dust of far the greatest importance in industry is dust of free silica (sio.) and the disease is often known as “ silicosis.” for a dust to be phthisis-producing it must be comparatively insoluble and inert and the particles must be minute, say from five microns downwards, or about the size of the common patho- genic micro-organisms. owing to their minute size these particles may be present in air in dangerous concentration without being visible to the eye or in any other way noticeable to the senses, so in a phthisis-producing industry it is expedient to sample the air for dust as one samples for gas in a ‘‘ gassy ” mine. the lungs and dust.—the lungs have a very considerable power of ridding themselves of inhaled particles, and some dusts, like coal-dust, are much more readily got rid of than others while, in the case of a phthisis-producing dust, accumulation readily gets ahead of elimination, so quite small quantities of air-borne dust may be dangcrous. it is owing to this cumulative factor that duration and continuity of exposure are of importance as well as concentration in the air. while the average incidence of miners’ phthisis on the gold-mines of the witwatersrand is under 3° per annum of the underground population the inci- dence rises as high as 10°%% per annum in the case of miners of 13 years’ service and over. dust cells —a certain proportion of the fine dust inhaled runs the gauntlet of the upper respiratory passages and gets right down into their minute blind extremities, the alveoli. in silicosis as in pulmonary tuberculosis ‘‘ lesion means arrest ”’ and the dust particles are arrested by being taken up by certain cells known as dust cells. the dust cells are a variety of the phago- cytes of metchnikoff and, when dust-laden, they aggregate to- gether forming small masses or pseudo-tubercles. these pseudo- tubercles may be found on the alveolar walls, under the pleura and in the lymphatic channels which they obstruct. the dust- containing cells forming the pseudo-tubercles tend to degenerate and become fibrous tissue thus forming the fibroid nodules char- acteristic of the early stage of silicosis. prevention—it is the fine dust that matters and, in mines where a phthisis-producing rock is dealt with, the chief sources of fine dust are blasting and rock-cutting with machines. from the point of view of prevention, in industries where blasting is practised, the workers should not return to the working-place until after all dust and fume have been blown away. ventilation with good currents of dust-free air 1s the great safeguard because, by treating the air-borne dust as a gas, it can be diluted down towards a safe level. what is a safe level? when one has to deal with daily exposure over many years, perhaps about one milli- gramme of dust per cu. metre of air. the fine dust is only a small proportion by weight of the total air-borne particles, but in- cludes the majority of particles by enumeration. a sample of air-borne dust of 2 milligrammes per cu. metre as determined by the method in use on the witwatersrand corresponds to about 350 particles of fine dust per cu. cm. of air (counted by kitze koniometer). the other great safeguard is “ working wet ” and the chief source of the dust associated with machine drilling is 925 “* sludging ” with air. when it is practicable to sludge with water only, machines raise much less dust. water-sprays should be in continuous use and the roof, walls and floor of the working-place kept wet. all broken rock should be thoroughly wetted before moving (see mining). a machine may be in good order for rock-cutting and in bad order for dust-control and should be inspected from the latter point of view as well as the former. a hand-drill is more difficult to keep in order for dust-control than is the larger machine and it is doubtful if it is possible to secure safe conditions 1f hand- drills are used dry when cutting phthisis-producing rock. in all phthisis-producing industries, apart from working wet, it 1s wise to think of the fine air-borne dust as a gas and make every pos- sible use of exhaust-hoods and abstractors; while sources of dust escaping to the air should, as far as possible, be located and en- closed. ‘there are two important factors in the severe forms of miners’ phthisis:— {rt} the phthisis-producing dust. (2) the tubercle bacillus. carriers —the modern view of pulmonary tuberculosis as met with in the adult population of civilised countries is that it is related to re-infection by the obvious route of inhalation, under experimental conditions the presence of dust in the air, together with the tubercle bacillus, renders the susceptible ani- mal much more liable to infection by inhalation. it ison account of this association that, in a phthisis-producing industry, one must strive not only to eliminate dust but also to eliminate the tubercle bacillus. the only practicable step towards the latter ideal is to detect and remove the “ carrier,” 7.c., the sufferer from open tuberculosis. for the sake of others as well as for their own, sufferers from tuberculosis should not be allowed to work at a phthisis-producing industry. tuberculosis, of course, is not a compensatible occupational disease, but it might well be so regarded in a phthisis-producing industry for, although pulmo- nary tuberculosis is not miners’ phthisis, practically all grave min- ers’ phthisis is associated with pulmonary tuberculosis. brbliograpiy.— public health (1915), with bibliography; tc. l. collis, industrial puetsmonoconioses, mulroy lectures, 1915 (1919); aunual reports of miners’ phihisis board and afiners’ phthisis medical burean, department of mines and industrics, union of south africa; publications of united states bureau of afines, 132, til. 372 eee. ca. mav.)