What is the Difference Between Petrography and Petrogenesis

The main difference between petrography and petrogenesis is that petrography involves the description and classification of rocks, especially by microscopic examination, while petrogenesis focuses on the origin and formation of rocks, especially igneous rocks.

Petrology is a branch of geology that focuses on rocks and their formation. Petrography and petrogenesis are two branches of petrology. Moreover, they focus on different aspects of rocks.

Key Areas Covered

1. What is Petrography 
     – Definition, Features
2. What is Petrogenesis
     – Definition, Features
3. What is the Relationship Between Petrography and Petrogenesis
     – Outline of Common Features
3. What is the Difference Between Petrography and Petrogenesis
    – Comparison of Key Differences

Key Terms

Petrography, Petrogenesis, Petrology

What is Petrography

Petrography is a branch of geology that focuses on detailed descriptions of rocks. Petrography is actually a subsection of petrology, which is a branch of geology that studies rocks and their formation. Moreover, petrography involves the composition, organization, and systemic description of rocks. This especially involves microscopic examinations of rocks. Furthermore, petrographer is the name given to a person who studies petrography. 

Rocks are classified according to the information acquired during petrographic analysis. This type of analysis may begin with field notes at the outcrop and include macroscopic descriptions of hand specimens. For petrographers, their most important tool is the petrographic microscope. This microscope helps them to analyze as well as determine their mineralogical and chemical characteristics.

Figure 1: Gabbro under Microscope – Thin Section

Other analytical methods or techniques also involve chemical analysis of the whole rock by atomic absorption, laser-induced breakdown spectroscopy, or X-ray fluorescence, and analysis of individual grains by electron microprobe or atom probe tomography. A detailed analysis of minerals by optical mineralogy is also important to understand the origin of rocks. When optical means are not sufficient, it is also possible to analyze the individual mineral grains from a rock sample by X-ray diffraction.

What is Petrogenesis

Petrogenesis is a branch of petrology that focuses on the origin and formation of rocks. Petrogeny is another name for petrogenesis. Moreover, it’s also important to note that we mainly use the term petrogenesis to refer to processes that form igneous rocks. However, it can also describe metamorphic and sedimentary processes.

Figure 2: Formation of Igneous Rocks

Igneous rocks are a type of rocks that form due to the solidification of lava or magma. Furthermore, the formation of igneous rock involves three stages: magma generation, magma differentiation and assimilation of crust.

Relationship Between Petrography and Petrogenesis

• Petrography and petrogenesis are two branches of petrology, which is a branch of geology that studies rocks and their formation.
• Both involve the study of rocks and their origins/formation.

Difference Between Petrography and Petrogenesis

Definition

Petrography is a branch of petrology that focuses on the description and classification of rocks, especially by microscopic examination, while petrogenesis is a branch of petrology that focuses on the origin and formation of rocks, especially igneous rocks.

Involves

Petrography involves the description and classification of rocks, especially by microscopic examination, while petrogenesis involves the origin and formation of rocks, especially igneous rocks.

Conclusion

The main difference between petrography and petrogenesis is that petrography involves the description and classification of rocks, especially by microscopic examination, while petrogenesis focuses on the origin and formation of rocks, especially igneous rocks.

Reference:

1. “Petrogenesis.” Wikipedia, Wikimedia Foundation, 18 Feb. 2021, Available here.
2. “Petrography.” Wikipedia, Wikimedia Foundation, 3 Jan. 2021, Available here.

Image Courtesy:

1. “Gabbro from Rum in Scotland – Thin Section” By Julien Leuthold (ETH Zürich, Switzerland) (CC BY 3.0) via Commons Wikimedia

2. “Igneous rock eng modified” By The Editor’s Apprentice – Own work (CC0) via Commons Wikimedia