University of California Publications. Bulletin of the Department of Geological Sciences Volume 4

University of California Publications. Bulletin of the Department of Geological Sciences Volume 4

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ...Disseminated throughout the matrix is a very large quantity of finely divided biotite, which serves to bring out the schistose structure of the rock. Its orientation around granulated areas of feldspar surrounding unshattered nuclei emphasizes the mode of reduction of the feldspars by attrition. An important variation of the gneissic quartz porphyry is a strongly schistose facies showing abundant patches of drawnout feldspar and a few augen of vitreous quartz. Upon the silvery white foliation planes of this schist are curious aggregates of sheared biotite disposed in irregular orientation. They are more or less rectangular in shape and cause the rock to simulate the appearance of the so-called "picture schists." In thin section a few shattered phenocrysts of quartz can be observed. However, one was noted which was entire and of uniform polarization tint, free from inclusions, and with but slight shadowy extinction. Its shape is such as to suggest its derivation from the dihexahedral form, but can not be conclusively demonstrated. Its boundaries are not geometric lines, but are crenulate. A peculiarity in the distribution of the interference colors suggests a well healed gash running across the phenocryst. In convergent light the section shows an eccentric uniaxial cross of a weakly birefringent mineral. The homogeneity and relatively large size of the quartz crystal, and the sharp plication of the lines of sehistosity caused by it, accentuate strongly its phenocrystic character. A few kaolinized and shattered phenocrysts of orthoclase also occur. The biotite is mostly flaky and is localized in bands. The groundmass is very fine grained and consists of quartz (?) more or less interwoven with sericite. Magnetite and zircon occur more

Product details

  • Paperback | 162 pages
  • 189 x 246 x 9mm | 299g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236635205
  • 9781236635204