Igneous Rock Classification & How to Use The QAPF Diagram- Igneous Petrology #1 | GEO GIRL

The first of a series of igneous petrology videos! This video covers igneous rock classification schemes, such as the QAPF diagram and how to classify rocks using these schemes. We also discuss the basics regarding composition and grain size of igneous rocks and how to use these features to identify igneous rocks. I start by going over what igneous petrology is and why we study igneous petrology. Mineralogy is the study of minerals, while petrology is the study of rocks. In igneous petrology we investigate how magmas are produced, how magmas ascend through the mantle and crust, the mineralogical and geochemical evolution of magmas throughout their ascent and eruption, & the emplacement and eruption styles of igneous lavas and magmas. The most basic classification of igenous rocks is based on grain size. Coarse-grained igneous rocks are called plutonic or intrusive, while fine-grained igneous rocks are called volcanic or extrusive. Plutonic and volcanic rocks are further classified by silica content. Felsic rocks are very rich in silica while mafic rocks contain much less silica. An example of a Felsic, plutonic rock is granite. a common example of a mafic, volcanic rock is basalt. The grain size of the rock tell us about whether it cooled at or below earth's surface, while the silica content tells us about its source magma composition. The IUGS created the QAPF diagram for classifying plutonic igneous rocks, and a separate graph for classifying volcanic igneous rocks. Ultramafic rocks are classified by an entire different scheme. I go through all the ingeous rock classification schemes in this video, hope you enjoy! ;)

References: Essentials of Igneous Petrology by Ronald and Carol Frost: https://amzn.to/3fJ94XD
Earth Materials by Cornelis Klein & Anthony Philpotts: https://amzn.to/3CwyBwY

GEO GIRL Website: https://www.geogirlscience.com/ (visit my website to see all my courses, shop merch, learn more about me, and donate to support the channel if you'd like!)

0:00 What Igneous Petrology is & importance
0:47 Importance of Mineralogy Before Petrology
1:22 Classification of igneous rocks
1:43 Classification by grain size (volcanic vs. plutonic)
4:32 Classification by silica (felsic vs. mafic)
5:51 Modal Mineralogy
10:23 IUGS QAPF Diagram
11:26 QAPF Diagram w/rock pictures
17:22 Ultramafic Rock Classification
19:18 IUGS Volcanic Classification
23:35 Textbooks used for this lecture!
24:25 Dog! (not mine, but adorable)

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