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

170 ECONOMIC GEOLOGY which when present in mass forms china-clay. It is so named from its use in China for making porcelain—a word invented by the Portuguese in support of the assertion that the material was made from the shells of a cowrie named Porcellano. One important occurrence of china-clay is at Kauling or “the high ridge ” near Jao-chow Fu, S. of the Yangtze-kiang and E. of Lake Poyang; Berzelius named china-clay Kaolin under the impression that it was the raw material of this ridge. Kaolinite—the crystalline form-is only one constituent, and is isolated by washing ; in Cornwall it forms on an average about a quarter of the mass. The careful washing for the finer qualities of Chinese porcelain Fic. 50.—A CHINA-CLAY Mass IN CorRNwALL., The dotted area represents the china-clay developed in the granite (shown by short lines); 4, a band containing biotite; Z, zircon crystals in the overlying soil ; none were found in the china-clay. Parallel lines, slate, kaolinized near the contact with the granite, Dark lines, tourmaline veins. has given rise to the statement that one man begins to wash the clay and his grandson makes the pot. China-clay in Cornwall and Devon (Fig. 50) occurs in deep blocks and pipe-like masses in granite, and it consists chiefly of quartz, white mica, kaolinite, tourmaline, and topaz. The quartz is in rounded corroded grains which from their shape and size have been compared to mulberries. The washed residue consists of a pure white clay composed of minute flakes of white mica and kaolinite. ~The kaolinite crystallizes in hexagonal scales which have a highly developed basal cleavage, and are very similar to muscovite mica. The tourmaline is of the black variety, schorl, and occurs in scattered crystals or in veins which may extend into the granite and are then bordered by china-clay. Small crystals of topaz are common ; flakes of biotite remain where it was

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