Geological Survey Bulletin Volume 1436

Geological Survey Bulletin Volume 1436

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: epidote. Some altered sphene is present, and a few carbonate veinlets cut the rock. The modal composition of the rock is difficult to determine, but it is estimated that quartz is approximately 14 percent, plagioclase 68 percent, potassium feldspar 9 percent, and mafic minerals 8 percent by volume. The nonmyrmekitic variety (table 4, no. 2) is medium grained and hypidiomorphic granular: the plagioclase tends to be subhedral; the other constituents are mostly anhedral. The plagioclase is sodic oligoclase to albite, commonly twinned, and is gray with abundant sericite. Quartz is anhedral, commonly lobate. A trace of potassium feldspar was revealed by selective staining of a sawed surface, but none was recognized in thin section. Mafic minerals include bluish-green hornblende and biotite, both partly replaced by chlorite. Minor amounts of muscovite are present. Table 4.--Chemical and spectrographic analyses of altered quartz diorite Rapid rock analyses by P. Elmore, J. Kelsey, H. Smith, and J. Glenn. Spectrographic analyses by Chris Heropoulos Description and location: 1. Altered myrmekitic quartz diorite (Y-39-69). SEW sec. 7, T. 42 N., R. 7 W., China Mountain quadrangle. 2. Altered quartz diorite (Y-48-71). SWW sec. 8, T. 42 N., R. 7 W., Yreka quadrangle. Accessory minerals include epidote, sphene, and very minor amounts of opaque minerals, chiefly secondary hematite. The specimen represented by sample 2 in table 4 is cut by a network of fine fractures filled with secondary minerals including prehnite, chlorite, minor sericite, and epidote. The estimated modal composition of the rock from a stained slab is quartz, -29 percent; plagioclase, 48 percent; and mafic minerals, 23 percent by volume, with a trace of potassium feldspar. Commonly these rocks..
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Product details

  • Paperback | 28 pages
  • 189 x 246 x 2mm | 68g
  • United States
  • English
  • black & white illustrations
  • 1236881788
  • 9781236881786