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

72 ECONOMIC GEOLOGY constant association of china-clay with tourmaline and topaz, and its absence from propylitic deposits due to steam com- bined with carbonic acid, indicates that its formation is pneumatolytic. Kaolinite is found in small quantities beside mineral veins in Anglesey. It has been formed in felspathic sandstones in Scotland ‘and the Midlands by superheated steam and carbonic acid from dykes having kaolinized the felspar grains; this kaolinite is therefore due to pneumato- hydrolysis. GerMAN DEPOSITS OF Various MoDpEs oF FormaTiOoN— The German china-clays are due to two processes. Some Loam., C.C. o.P Fie. 51.—CHINA-CLAY. China-clay (C.C.) resting upon and passing down into quartz-porphyry (Q.P.) at Baselitz (after Stahl). of the most important deposits, such as those at Meissen that are used for Dresden china, are due to descending waters charged with sulphuric acid produced by the decom- position of pyrites from brown coal. These china-clays occur as superficial sheets, which pass into the country rock, which at Meissen and Baselitz (Fig. 51) is quartz-porphyry and Brown Coal Clay & 3 nd’ Quartz Porphym.: Frc. 52.—CHina-Cray. China-clay produced by the action of acids from brown coal in Bavaria on guartz-porphyry (after Stahl). volcanic tuff, and elsewhere the china-clay occurs where brown coal beds rest against quartz-porphyry (Fig. 52). These deposits do not contain tourmaline, except where, according to Stahl, it existed in. the original granite, and biotite is rarely preserved. Roesler attributes the formation of this china-clay to solutions rising through fissures: but

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