A descriptive petrography of the igneous rocks. v. 3

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• 责任者：Johannsen ; A.
• 责任方式：Written
• 出版者：The University of Chicago Press
• 出版年：1937
• 出版地：Chicago
• 出版日期：1937/1/1 0:00:00
• 分类号：360
• 语言：English

摘要

Since the publication of Volumes Ⅰ and Ⅱ of this Petrography, I have given very serious consideration to the question of changing the limits of the various classes in the rock classification from 0-5-50-95-100 per cent dark minerals to 0-5-45-85-100 per cent, 0-10-40-70-100 per cent, or some such values, to make Class 3 embrace rocks a little less melanocratic than fixed by the 50-50 point, and Class 4 embrace rocks with a little higher percentage of leucocrates.