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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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

THE MINERAL FERTILIZERS 203 consist of carbonate of lime, which is altered to phosphate of lime. The phosphate may at first form a thin impermeable crust which may be broken by the collapse of solution cavities in the underlying limestones, and the pieces are cemented into phosphate breccia. In volcanic islands the phosphoric acid produces phosphate of alumina, such as the phosphatized trachyte of Clipperton Island in the Pacific Ocean off Mexico. Phosphate of alumina is more expensive to convert into superphosphate, and less valuable as a fertilizer than phos- phate of lime; it is used for some special purposes, such as the treatment of sewage. The phosphate of Christmas Island south of Java includes phosphatized volcanic rocks and coral reefs, and phosphatic breccia; and these rocks are traversed by thin veins of staffelite, a fibrous and concretionary variety of fluo-apatite, which show that the phosphoric acid was introduced in solution, doubtless as Andrews suggested from once overlying guano Nauru was discovered in 1798 and named Pleasant Island. A block of rock from it, regarded as fossil wood, was used in Sydney as a door weight. The recognition of its nature led to the discovery that Nauru and Ocean Islands contain about 100 million tons of high-grade phosphate. Cargoes are shipped averaging 85 to 88 per cent. of tricalcic phosphate (CagP,0g). The phosphate occurs in depressions between pinnacles of limestone, and it does not pay to work deeper than 20-30 feet. H. B. Pope (Austral. Indust. and Min. Stand., 15 February, 1923) regards the phosphate as derived from bird guano, though few birds live on the islands at present (cf. L. Owen, 0.7.G.S., 1xxix, 1923, pp. 1-14). Lagoon PHOspHATE—Some important beds of phosphate of lime are formed in tropical and subtropical lagoons. Dead animals are washed into them and their bones and fish remains collect in patches, whence the current sweeps away the finer sediment. The bones may be dissolved and re- deposited in nodules of earthy phosphate of lime, which are then known as coprolites. The term coprolite was given to the fossil dung of reptiles LC. W. Andrews, Monogr. Christmas Island, 1900, pp. 290-1. The staffelite veins are described by the author, 77. G. Soc. Glasg., xvi, 1917, p. 134, pl. VL.

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