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Image from page 112 of "Minerals in rock sections; the practical methods of identifying minerals in rock sections with the microscope, especially arranged for students in technical and scientific schools" (1905) | by Internet Archive Book Images
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Image from page 112 of "Minerals in rock sections; the practical methods of identifying minerals in rock sections with the microscope, especially arranged for students in technical and scientific schools" (1905)

Identifier: mineralsinrockse00luqu

Title: Minerals in rock sections; the practical methods of identifying minerals in rock sections with the microscope, especially arranged for students in technical and scientific schools

Year: 1905 (1900s)

Authors: Luquer, Lea McIlvaine, 1864-

Subjects: Petrology

Publisher: New York : D. Van Nostrand company

Contributing Library: University of California Libraries

Digitizing Sponsor: Internet Archive

 

 

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Text Appearing Before Image:

FlG. 67. — Micro-pegmatitic structure, in granophyric quartz-porphyry. (FromCohen.) .sition has commenced ; and in fresh crystals may be indicated byzonal arrangement of inclusions. Tiviiiiiitig.—Very common, generalh after Carlsbad\ayN, Figs. 18 * See under quartz, p. 60. FELDSPAR GROUP. 97 and 69 ; the twinning boundary, dividing the section longitudinally,either being parallel to edges of crystal or bent or jagged. Twin-ning after Bavcno (twinning boundary diagonal, \\\\\\ the two partsextinguishing at the same time, but having a and c directions,crossed in the two portions) and Ma)iebacJi laws less common * Color.—Colorless or tinged by oxide of iron. Cloudy if decom-posed. Index of Refraction.—n = 1.523, hence no relief and surfacesmooth. Cleavage.—Varies and sometimes only seen in very thin sec-tions, but is an important character and should always be searchedfor. It occurs perfect, parallel to base (OP, 001), and almost as

 

Text Appearing After Image:

Fig. 68. — Orthoclase, ortho pinacoid section showing cleavages intersecting at 90°,in augite-syenite. perfect parallel to clino pinacoid (co P ^ , 010). The two cleavagesintersect at 90° in sections parallel to the b axis, Fig. 68. Inclusions.—May be present and arranged in regular or zonalorder, but not important. Do not occur in individuals of a secondgeneration.Polarized Light: Pleochroisni.—None. Crossed Nicols: Double Refraction.—Very weak (-^ — « = 0.007). Interference Colors.—Lower first order, gray, white, etc., notquite so bright as colors of quartz and plagioclase. Extinction.—Being monoclinic the extinction angle on base (OP. * Iddings Rose7ibiisch, p. 306.7 9^ CflARACTERS OF MIXERALS. ooi), with reference to clino pinacoid (co P cc , Oio) cleavage cracks,is o°. On clino pinacoid, with reference to basal cleavage cracks,it is 5°. Some sections (notably in glassy sanidine grains) mayappear dark during complete rotation. This is due to the factthat the axi

 

 

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