Bulletin of the Department of Geology of the University of California Volume . 1

Bulletin of the Department of Geology of the University of California Volume . 1

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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. 1896 edition. Excerpt: ...Potrero, San Francisco. This Bulletin, Vol. I, No. 5, p. 164 Under the microscope the rock shows a somewhat cloudy, colorless substance, speckled with grains and irregular aggregates of magnetite. With crossed nicols, the colorless groundmass is resolved into a confused aggregate of serpentine in lamella:, fibers, and grains, polarizing in low tints of gray and yellow. Occasionally the fibers are arranged at right angles to each other, giving suggestions of the "grate structure," but it never goes farther than a suggestion. A few remnants of large crystals of some brightly polarizing mineral with pronounced cleavage and inclined extinction are also present, and have been determined in fresher specimens as diallage. An analysis of the serpentine of one of the harder nodules is given in column II of the table of analyses (p. 231). During the chemical examination, it was found that some of the supposed grains of magnetite were not decomposed by acids, and gave a distinct chromium reaction in the borax bead. On the other hand, the microscopic slides show none of the brown translucent chromite that is to be seen in the serpentine from Tiburon. Although the foregoing may be taken as a general description of the serpentine, there is more or less variation observable in the mass. Some slides consist almost wholly of serpentine in finely felted fibers, others show varying amounts of magnetite and perhaps chromic iron, and some contain remnants of pyroxene crystals. No olivine has been detected in any of the sections, nor can the former presence of rhombic pyroxene be shown with certainty. At the northern extremity of the dyke, down on the beach, the rock exhibits a different facies from that previously described. It is here much less sheared and...show more

Product details

  • Paperback | 154 pages
  • 189 x 246 x 8mm | 286g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236532775
  • 9781236532770