Editing Petrography (section)

{{short description|Branch of petrology focusing on detailed descriptions of rocks}}
{{One source|date=October 2016}}
{{distinguish|petroglyphs}}
'''Petrography''' is a branch of [[petrology]] that focuses on detailed descriptions of [[rock (geology)|rocks]]. Someone who studies petrography is called a '''petrographer'''. The [[mineral]] content and the [[Rock microstructure|textural]] relationships within the rock are described in detail. The classification of [[rock (geology)|rock]]s is based on the information acquired during the '''petrographic analysis'''. Petrographic descriptions start with the field notes at the [[outcrop]] and include macroscopic description of hand-sized specimens. The most important petrographer's tool is the [[petrographic microscope]]. The detailed analysis of minerals by [[optical mineralogy]] in [[thin section]] and the micro-texture and structure are critical to understanding the origin of the rock. 

[[Electron microprobe]] or [[atom probe]] tomography analysis of individual grains as well as whole rock chemical analysis by [[atomic absorption]], [[X-ray fluorescence]], and [[laser-induced breakdown spectroscopy]] are used in a modern petrographic lab. Individual mineral grains from a rock sample may also be analyzed by [[X-ray diffraction]] when optical means are insufficient. Analysis of microscopic [[fluid inclusions]] within mineral grains with a heating stage on a petrographic microscope provides clues to the temperature and pressure conditions existent during the mineral formation.