Harriman Alaska Series; Geology and Paleontology

Harriman Alaska Series; Geology and Paleontology

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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. 1910 edition. Excerpt: ...which is less abundant than the labradorite, offers many points of interest. It is in anhedra with subangular and often rounded and deeply embayed outlines. Some are quite unaltered; more frequently the whole centre of the crystal is granulated, the grains of orthoclase showing wavy extinctions, the border also orthoclase, but in a single individual with uniform extinction throughout; again, with the same orthoclase border as in the last, the centre is occupied wholly by fibrous chlorite, and in a final stage the chlorite occupies the whole space. In some crystals the granular orthoclase and the chlorite are intermingled with grains of augite, and it appears as if the chlorite were derived from the decomposition of the augite. But there must also have been replacement of feldspar substance by chlorite in the largely or wholly chloritized crystals. The embayed outline of the orthoclase crystals suggests that they were the first separation from a magma which afterwards attacked them, in part dissolving, in part granulating the mass of the crystal. Thus weakened in structure, the crystals have been peculiarly subject to the attack of decomposition, and have been largely replaced by chlorite, derived in part from augite inclusions in the orthoclase, in part from the groundmass of the rock. The augite is in sharply-bounded short prisms, showing octagonal cross-sections. It is colorless, and in some cases is in process of alteration to chlorite. Magnetite grains are sparingly present. The presence in this rock of orthoclase, together with a basic plagioclase and augite, places it in the latite series, intermediate to trachyte and andesite. Without a chemical analysis it is difficult to define the type more closely, but in its mineralogical composition...show more

Product details

  • Paperback | 50 pages
  • 189 x 246 x 3mm | 109g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236513398
  • 9781236513397