The Elements of economic geology

Bibliographic data

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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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

60 ECONOMIC GEOLOGY electrical apparatus, and worth sometimes 7d. per Ib.; No. I contains pieces of 24 to 36 square inches and are worth, according to clearness, from 10s. to 30s. per Ib. ; extra special sizes may sell for 37s. per lb. The economics of mica mining may be illustrated by the results at Kodarma in Bihar. Each miner obtained an average of 32 lb. of rough mica per day; this yielded 4 Ib. of cut mica. If this had all been No. 7 mica at 7d. per lb., the yield would only have been 2s. 4d. per man, but its average price before the War was 0s. per 1b., and as wages were 6d. per day, the yield was profitable. ASBESTOS Asbestos (from a Greek word meaning inextinguishable) is a fibrous mineral which is non-inflammable, and a bad con- ductor of heat, and is produced by the decomposition of several magnesian silicates. Flexible fibres are woven .into fire- proof cloth ; others are used for making heat-proof tiles and packing, filters, and cement; the largest use at present is in motor car brakes and clutches. The most important variety is chrysotile asbestos, a fibrous serpentine worked chiefly in Canada, Rhodesia, the Ural Mountains, and Cyprus. The main asbestos field is at Thetford and Black Lake in Quebec. The asbestos occurs in veins in a thick sill of Devonian peridotite, diabase, and porphyry, which contains veins and masses of pegmatite, granite, and aplite. The best asbestos js said to occur abutting against the aplite, and asbestos tufts occur in its quartz. The serpentine is due to the alteration of peridotite, and contains masses and lenticular streaks of it. The ser- pentine is traversed, often along shearing planes, by veins of asbestos up to 3—6 inches thick. The fibres are at right- angles to the vein, and have formed by recrystallization of the serpentine along both sides of a fissure. A variety, locally called fibrolite, at the Vimy Ridge Quarry has longer but more brittle fibres. The asbestos has been worked in long open cuts, now 350 feet deep, and has been proved by boring down to 800 feet. The fibre is separated from the crushed rock by shaking tables and air suction, and amounts on an average for the district to 4 per cent. of the rock. Tremolite or Italian asbestos is worked in Piedmont. and has

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