The geology of the Coromandel subdivision, Hauraki, Auckland . ed pyroclasticsalready described. Banded and Spherulitic Rhyolites.—Massive rhvolites. although abundant in the area under descrip-tion, are all in such an advanced state of surface decomposition that it is difficult to obtain even fairlyfresh specimens. The prevailing rock appears to be a pinkish-grey rhyolite consisting almost entirelyof spherulites, ranging from £ in. in diameter down to microscopic dimensions, with small glisteninghexagonal and irregularly shaped flakes of biotite. A few small crystals of quartz and feldspar ar
The geology of the Coromandel subdivision, Hauraki, Auckland . ed pyroclasticsalready described. Banded and Spherulitic Rhyolites.—Massive rhvolites. although abundant in the area under descrip-tion, are all in such an advanced state of surface decomposition that it is difficult to obtain even fairlyfresh specimens. The prevailing rock appears to be a pinkish-grey rhyolite consisting almost entirelyof spherulites, ranging from £ in. in diameter down to microscopic dimensions, with small glisteninghexagonal and irregularly shaped flakes of biotite. A few small crystals of quartz and feldspar arealso visible. Sections of the rock under the microscope show a mass of closely compressed spheru-lites of smoky-brown colour, which only feebly transmit light between crossed nicols. Plates of deep-brown strongly pleochroic biotite, grains and small crystals of quartz, plagioclase, and orthoclase,are interspersed throughout the spherulitic mass. * Rocks of Cape Colville Peninsula. vol. i. 1005, p. 220. t Loc. cit, vol. i. 1905, pp. 123, 124. PLATE %k >
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Keywords: ., bookcentury1900, bookdecade1900, bookidgeolog, booksubjectgeology
