The textural features of magmatic rocks have been described with the emphasis placed upon their relationship to the crystallization sequence of the magma. Examples have been chosen from the basaltic and diabasic dikes in the vicinity of Cornucopia, Oregon, the shonkinite-granite porphyry sequence at Yogo Peak in the Little Belt Mountains of Central Montana, and a few other localities. The textural differences of the orthomagmatic as compared to the late magmatic or deuteric pattern of crystallization have been noted. Where it has appeared that the deuteric fraction had been involved in mass flowage the term deuteromagmatic is suggested.
For metasomatic rocks, textural features to illustiate various stages of crystal growth have been described, such as the development of porphyroblasts, glomeroblastic aggregates, and the final crystalloblastic pattern. Most of the examples are taken from occurrences near Cornucopia, Oregon, and Buffalo Hump, Idaho, with a few references to other localities.
The textural features resulting from the mobilization of metasomatized rocks, such as rheomorphic dikes and rheomorphic breccias have been briefly noted. These commonly show magmatic textures superposed on metasomatic ones. For many igneous rocks, however, later crystalloblastic textures are superposed on the earlier orthomagmatic textures. Textural features alone are not always adequate for petrogenetic interpretations but for some occurrences like granitic intrusions they may furnish clues as to whether the body has evolved from an orthomagma or from mobilized metasomatized material, namely a neomagma.