The Quarterly journal of the Geological Society of London . ons to determine the biaxial character of the brightly polarizing crystals have been frequently Hatch, for example, refers them to muscovite or kaolin *.riagioclase is represented in the Soul granite by smaller crystalsexhibiting extinction-angles agreeing with those of and muscovite are found associated as secondary products,infilling cracks in the rock. Most of the biotite originally existingin the rock has been converted into chlorite, which exhibits thepleochroism : E = yellowish-gre
The Quarterly journal of the Geological Society of London . ons to determine the biaxial character of the brightly polarizing crystals have been frequently Hatch, for example, refers them to muscovite or kaolin *.riagioclase is represented in the Soul granite by smaller crystalsexhibiting extinction-angles agreeing with those of and muscovite are found associated as secondary products,infilling cracks in the rock. Most of the biotite originally existingin the rock has been converted into chlorite, which exhibits thepleochroism : E = yellowish-green, 0 = dark green, and Avhich, whentreated with sulphuric acid, decomposes with the formation ofgelatinous silica. Of accessory minerals, magnetite occurs, and lessabundantly apatite. In the coarse-grained granite of Soul there occur veins of a muchfiner-grained dark grey biotite-granite. Many of the crystals inthis rock seem to exhibit signs of growth after the formation of theoriginal crystal-outline (iig. 1). Much of the quartz, by intergrowth Pi^. Crystal of ortlioclase showing secondary extension of the felspathic material,irregularly intergrow ing with the neighbouring crystals. In biotite-granitefrom the mountains north-west of Soul. ?with the other crystals in the rock, produces a distinct pegmatiticBtructure. Colourless acicular inclusions are common in the the felspars, both orthoclastic and plagioclastic, are dis-tinctly kaolinized, the biotite has undergone little or no apparentalteration; chlorite is present in very small quantities. Near the boundary between the provinces of Kyong-kwi Do andChhung-chhong Do, between Yukei and Eumsong, and for somemiles around the latter town, there is an extensive development of * The Spheroid-bearing Granite of Mullaghderg, Co. Donegal, Geol. Soc. vol. xliv. (1888) p. 550. MR. T. H. HOLLAND ON ROCK-SPECIMENS FROM KOREA. 175 granitic rocks, breaking through the crystalline schists in that area,uii
Size: 1415px × 1766px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1840, bookidquarte, booksubjectgeology
