Radioactivity.—The strong radioactivity of uranium minerals
affords a ready means of recognizing 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 glass or vulcanite (say the
mouth-piece 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 piece 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 estimates have been made of the age in years of these minerals and even of the age of the earth; but, of course, many unknown factors must have been omitted from such calculations. Lead of radioactive origin, or isotopic lead the final product of the decay of uranium is found to vary slightly in its atomic weight according to the uranium mineral from which it is extracted.
To radioactivity is ascribed the well-known “pleochroic haloes”—tiny spots or borders of deeper colour surrounding microscopic inclusions—long ago observed in certain rock-forming minerals (cordierite, andalusite, mica, etc.) when micro-sections of rocks are examined in polarized light. The long and 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 0.04 mm. A study of these has again given some information as to the age of the minerals. In this connexion 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, Röntgen rays and the rays emitted by radium salts. For example, some diamonds acquire a green colour, and fluorspar becomes blue when placed in contact with radium bromide.
New Minerals.—In descriptive mineralogy a considerable number of new minerals have been named, but unfortunately in many cases not completely determined and described. A few of the more prominent and well-established of these are:—
Alamosite, lead metasilicate, PbSiO₃, found at Alamos, Sonora, Mexico, as radially fibrous masses with snow-white colour and adamantine lustre. Crystals are monoclinic, and the mineral is analogous to wollastonite (CaSiO₃).
Amosite, a variety of monoclinic amphibole-asbestos rich in iron (FeO 32.44%) and consisting essentially of ferrous silicate with but little magnesia. It is of the “cross-fibre” type and resembles crocidolite in its mode of occurrence, thus differing from the ordinary type of amphibole-asbestos. It is found over a wide area in northeastern Transvaal and is named from the Amosa asbestos mine, this word being formed of the initial letters of the company “Asbestos Mines of South Africa.”
Betafite, a hydrated titano-columbate of uranium containing UO₃ 26.28%. It occurs in pegmatites near Betafo in Madagascar as sharply developed octahedral crystals with the edges truncated by faces of the rhombic-dodecahedron. Curiously flattened crystals are also found.
Carnotite, hydrated vanadate of uranium and potassium, K₂O·V₂O₄·2U₂O₃·3H₂O, occurring as a canary-yellow crystalline powder impregnating sandstones over a wide area in western Colorado and the adjoining portions of Utah and New Mexico. In 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.
Inyoite, hydrated calcium borate, 2CaO·3B₂O₃·13H₂O, found as large, colourless, monoclinic crystals in the borate deposits of Inyo county, Cal., and in the gypsum mines at Hillsborough in New Brunswick.
Lorandite, sulpharsenite of thallium, TlAsS₂, forming transparent, 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 element thallium as an essential constituent (Tl 59.5%).
Margarosanite, metasilicate of lead and calcium, PbCa₂(SiO₃)₃, occurring as colourless or snow-white, platy masses and anorthic crystals with pearly lustre. It has been found at Franklin in New Jersey and at Långban in Sweden.
Otavite, basic carbonate of cadmium (Cd 61.5%), occurring as
small, pearly white, curved rhombohedra on copper and lead ores at
Otavi in South-West Africa. The only cadmium mineral previously
known is the sulphide, greenockite.
Patronite, vanadium sulphide, VS₄, forming dark, greenish-black, compact masses. It occurs abundantly at Minasragra, Cerro de Pasco, Peru, where it is a valuable ore of vanadium. It 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(PO₄)₂·Zn(OH)₂·3H₂O, forming pearly white, scaly cleavage masses and small monoclinic crystals. It has been found in some abundance forming large stalactites in a cavern near Salmo, British Columbia.
Stichtite, hydrated basic carbonate of magnesium and chromium, MgCO₃·5Mg(OH)₂·2Cr(OH)₃·4H₂O, occurring as foliated masses with pearly lustre and bright lilac colour. This colour forms a striking contrast to the bright green serpentine in which the mineral is embedded. It has been found in western Tasmania, in the Transvaal, and near Black Lake in Quebec.
Tarbuttite, basic zinc phosphate, Zn₃(PO₄)₂·Zn(OH)₂, 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.
Thortveitite, silicate of scandium, yttrium, etc. (Sc,Y)₂O₂·2SiO₂, occurring as large orthorhombic crystals of prismatic habit in pegmatite in southern Norway and Madagascar. This is the only mineral known to contain the rare element scandium in large amount.
Tungstenite, tungsten sulphide, WS₂, forming minute scales resembling molybdenite and graphite in appearance. It is found intimately intermixed with other ores in the Little Cottonwood district, Utah.
References.—Details of descriptive mineralogy are collected in Appendices 1-3 of Dana's System of Mineralogy (New York 1899-1915); and numerical data respecting the constants of minerals are tabulated in the international Tables annuelles de constantes et données numériques (4 vols., Paris 1912, etc.). A new work of a comprehensive character is C. Doelter, Handbuch der Mineralchemie (3 vols., Dresden and Leipzig 1912, etc.). A number of elementary text-books have been published, e.g. F. H. Hatch, Mineralogy (London 1912); G. A. J. Cole, Outlines of Mineralogy for Geological Students (London 1912); A. F. Rogers, Introduction to the Study of Minerals (New York 1912); A. H. Phillips, Mineralogy, an Introduction to the Theoretical and Practical Study of Minerals (New York 1912); E. H. Kraus and W. F. Hunt, Mineralogy, an Introduction to the Study of Minerals and Crystals (New York 1920). A popular book with coloured plates is L. J. Spencer, The World's Minerals (London 1911). Books of an economic character are H. Ries, Economic Geology (4th ed., New York 1916); T. Crook, Economic Mineralogy, a Practical Guide to the Study of Useful Minerals (London 1921); B. Dammer and O. Tietze, Die nutzbaren Mineralien (2 vols., Stuttgart 1913-4); O. Stutzer, Die wichtigsten Lagerstätten der “Nicht-Erze” (Berlin 1911, etc.). New journals are Fortschritte der Mineralogie, Kristallographie und Petrographie, ed. by G. Linck (Jena since 1911); Beiträge zur Kristallographie und Mineralogie, ed. by V. Goldschmidt (Heidelberg since 1914).
(L. J. S.)
MINESWEEPING AND MINELAYING. Among the naval
services rendered to Great Britain and the Allies during the World War, none were more conspicuously important than the work of British minesweepers and minelayers; and minelaying was a large item in the naval war record of Germany.
Mines-weeping. As early as 1907, Adml. Lord Charles Beresford, when commander-in-chief of the British Home Fleet, had recommended the use of Grimsby trawlers for the service of minesweeping. A trawler reserve, R.N.R. (T.), had been constituted under an inspecting captain of minesweeping vessels, and the system worked so well that by Aug. 8 1914, 96 hired trawlers had put to sea. The needs of minesweeping had, however, only partly been foreseen. When the war broke out the only minesweepers with the fleet were six torpedo gunboats fitted with the “A” sweep, a single wire kept at a required depth by waterkites and towed between two sweepers 500 yd. apart. It soon became evident that minelaying played an important part in German strategy, and after the “Amphion” had been sunk on the field laid off Aldeburgh by the “Konigin Louise” on Aug. 5, a hundred additional trawlers were ordered and Lowestoft became the principal minesweeping base on the east coast. On Sept. 1 Rear-Adml. E. Charlton was appointed Rear-Admiral Minesweeping on the East Coast, in charge of minesweeping operations and technical arrangements, leaving the inspecting captain to attend to the business of supply.
Minesweeping at this time was largely in the experimental stage and some time elapsed before it was able to cope with the magnitude of its task. One of the first steps taken to ensure the safety of shipping was the institution of a war channel up the east coast, clearly marked by buoys 2 m. apart, from the Downs, past the Shipwash, Newarp and Cromer's Knoll to Flamborough Head. This was swept daily by local trawler flotillas and provided a safe channel up the east coast. Trawlers, how-
