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

CLAY 173 the evidence cited by Barnitzke (Z. praki. G., xvii, 1909, p. 471) and A. Stahl (Arch. Lag., xii, 1912) favours the descend- ing movement of the acid water. Stahl has called such china-clay exogenous as due to alien waters, in contrast to the endogenous, which is due to waters acting during the original formation of the associated deposits. Some of the latter group, e.g. those of the Naab Valley in Bavaria, are due to pneumatohydrolysis, being due to ascending carbonic acid solutions which are there connected with basalt {Stahl, #bid., p. 128). The German china-clay is formed by both plutonic and meteoric waters. Those china-clay deposits in the United States that are kaolinized acid dykes may be due to meteoric water. The china-clay stocks of Victoria are associated with tourmaline, and are of pneumatolytic origin. China-clay is used for many purposes. Its price usually varies between £I and £2 per ton. Its most important use is for porcelain owing to its purity in colour and resistance to high temperatures. Impure varieties are used for refractory bricks. As china-clay is easily moulded, it is used for the manufacture of wall-paper with a raised surface; as it is inert and innocuous it has been used as an adulterant for confectionery and ice creams. FuLrer’s Earta—Fuller's earth differs from clay by being usually non-plastic. It is an amorphous hydro- silicate of alumina similar to halloysite; it is very fine in grain and has the property of absorbing grease and colouring matters. It was formerly used to remove grease from wool during the process known as fulling; its main present use is for the filtration of oils, and as a constituent of paper, soap, and drugs. Fuller's earth is generally interstratified in shallow water marine deposits which often contain glauco- nite. It was apparently laid down under conditions in which silicate of alumina was deposited as a fine clay mixed with a little sand composed of quartz or felspar, and often some carbonate of lime. It generally contains about 70 to 80 per cent. of silicate of alumina, from 4 to 10 per cent. of ferric oxide, from 1 to 5 per cent. of carbonate of lime, from I to 2 per cent. of alkalis, and 8 to 25 per cent. of water. The material owes its absorptive properties to the minute size of its particles, which offer a large area for surface

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