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

58 ECONOMIC GEOLOGY are isolated in schist or gneiss, and must have been formed by its recrystallization. As the mica is associated with tour- maline, fluorite, topaz and china-clay, it must have been formed pneumatolytically by super-heated steam containing boric and fluoric acids. The original rock has been replaced by huge crystals of quartz, felspar (usually microcline), and “books” of mica. The quartz may form the core of a mass or the middle of a sheet of pegmatite (Fig. 48). The mica books usually occur at the contact of the pegmatite with this quartz or with the country, especially where the ountry rock is strongly micaceous. Phlogopite, a brown magnesian mica, is of especial value for electrical purposes because it is softer than muscovite F16. 48—THE ForMaTION OF Mica IN Gne1ss, Kenva CoLony. {Gn.), A pegmatite vein (P) with iso- lated pegmatite bodies (P) in the gneiss. The core of the pegmatite Consists of quartz, Q. Muscovite * books *’ especially abundant near the quartz. Cn and rubs away at the same rate as copper. Bearings with phlogopite insulators wear evenly. The chief field is in Ottawa, Canada, where the gneiss and crystalline limestones are intersected by veins or masses of pyroxenite. According to some authorities (e.g. A. Osann, Ann. Rep. G.S. Canada, Xii, 1002, p. 21) the pyroxenite is intrusive ; according to F. D. Adams and Barlow (G.S. Canada, Mem. 6, 1910, pp. 88-90) it is altered limestone. In some cases, such as the Loughboro’ Mine (Fig. 49 after Schmid, Mica, Canada Dept. Mines, No. 118, 1912, P- 147), the pyroxenite would appear intrusive into the gneiss; both rocks were covered un- conformably by limestone ; subsequently superheated acid water containing magnesia rose through the pyroxenite and

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