Petrology: Condensed and Simplified

The Study of rocks without the aid of a compound microscope or chemical analyses constitutes the science of petrology. The usual aim of a student of this science is to classify or assign names to rocks in the field. All that is said herein applies to what may be seen in rocks by the use of no aid to the eyes but a hand lens. Rock identification thus attempted is not as easy or conclusive as are most instances of mineral identification inasmuch as all rock species except most chemical precipitates, later discussed, are transitional by imperceptible degrees into other species, and many are so fine-grained that their constituents cannot be determined even with a hand lens. Alteration that results from exposure to atmospheric agents at or near the earth's surface may also make identification uncertain. Nevertheless, it is highly desirable for geologists and mining engineers to be able to attach names to rocks they encounter, even if many of these names must be considered tentative subject to correction after later detailed laboratory study. Fortunately, a skilled petrologist will find that a large majority of his tentative identifications will not have to be then changed. 29 p.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact azgs-info@email.arizona.edu