The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part II. Ore deposits

Collection:: Economics Books

ORES OF ALUMINIUM 153 from bauxite, of which there are large supplies in the tropics and warm temperate zones. The production of aluminium has increased rapidly in recent years; the total output in 1913 was 70,000 tons, which the stimulus of the War raised to 178,000 tons in 1918, and after a fall to 67,000 tons in 1921, increased to 190,000 tons in 1925. The modern production is mainly from the mixed mineral bauxite, which was described by Berthier in 1821 from Les Baux near Arles in the S. of France; it contains 52 per cent. of alumina. An allied material from Southern India had been named laterite by Buchanan in 1807; it is an oxide of alumina associated with ferric oxide, titanium oxide, and water. Laterite is a superficial decom- position product of various rocks, and especially basalt, in warm countries with a long dry season. Bauxite—Bauxite has been often regarded as a mineral species with the composition Al,O,, 2H,O, and therefore intermediate between diaspore, AlO;, H,0, and gibbsite, ALO, 3H,0, and also allied to wocheinite, 2A1,0,, 3H,0. Some bauxite is a mixture of equal parts of gibbsite and diaspore, and some of that in India, according to C. S. Fox (Mem. G.S. India, xlix, 1923, p. 21) consists of gibbsite mixed with amorphous alumina and iron oxide. = Bauxite and laterite pass into one another, the laterite having more iron and bauxite more alumina. Both are formed by the de- composition of silicate of alumina and removal of silica. Silicate of alumina is usually stable, but is decomposed in nature by three processes. Where rain-water soaks into the ground and acts upon it slowly in the presence of carbon dioxide and organic matter or—as suggested by Sir Thomas Holland (Geol. Mag. 1003, p. 63) of primitive organisms such as bacteria—the silicate is decomposed ; the water carries silica into the rivers in solution (e.g. Sir J. B. Harrison, Rep. Geol. Brit. Guiana, 1898, p. 19), or deposits it as veins of quartz, leaving free alumina which is widespread in tropical soils. The alumina is often deposited in rounded concentric bodies or pisolites. This process is especially effective where hot dry seasons alternate with periods of heavy rain, where the slope is gentle, so that the rain soaks Into the ground, and at levels, as below 5000 feet in India, where the average temperature is high throughout the year.

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