The Roman Comagmatic Region

The Roman Comagmatic Region

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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: ...marked, and inclusions are not common. The subhedrally prismatic augite phenocrysts are of the usual pale-gray color, though in some specimens there is a tendency to zonal growth, as shown by a slight deepening of the greenish tint toward the center or by progressive extinctions. The groundmass is holocrystalline in nearly all the specimens examined, the fabric is intersertal, and it is composed in great part of leucite, partly in the form of small, subhedral spheroids, and partly in quite irregular anhedra. All these are clear and carry few if any inclusions. With these leucites are many small feldspar laths, the majority being of a twinned labradorite about Ab2An3, with fewer of alkali-feldspar, which is also present to some extent as an interstitial cement in patches. The arrangement of these feldspar laths is diverse, producing an intersertal fabric. Small augites are also abundant in stout subhedral prismoids, often so short as to be almost equant. The gray color of this is also slightly more greenish than is usually true of the rocks of the region, though the absence of pleochroism indicates that it does not carry any of the aegirite molecule. Small magnetite grains and apatite prisms are present, both in rather greater amount than is usually the case in similar rocks elsewhere in the region, but no olivine could be detected. In some of the specimens there is some colorless nephelite as an interstitial base, the last product of solidification, while in a few this is partly replaced by a colorless glass, the amount of which, however, is never great. Chemical composition.--Of this type two hitherto unpublished analyses are given. In III is found an earlier analysis of the same specimen as that used for II, in which MgO was determined more

Product details

  • Paperback | 92 pages
  • 189 x 246 x 5mm | 181g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236642511
  • 9781236642516