An Introduction to the Study of Petrology - The Igneous Rocks #244796

Petrology is that department of geological science which has for its object the investigation of the characters and relations of rocks, that is to say, of the various materials of which the earth's crust is built up. A. Rock may be defined as a mineral aggregate, possessing a more or less persistent geological charac ter. In studying rocks, therefore, we have three points of departure: (1) their geological relations, or mode of occurrence (2) their constituent minerals; and (3) the mode of aggregation of the constituent minerals, or rock-structure.