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In Igneous Petrology, you need to identify igneous rocks and the minerals those rocks are made of in both hand specimen and thin section. In this video, I show images of hand samples and thin sections of the following:
- Basalt: Fine-grained, extrusive/volcanic, & mafic cooled lava, containing plagioclase and pyroxene (typically, clinopyroxene, such as augite), & sometimes other minor minerals, such as quartz, hornblende, biotite, orthopyroxenes (such as hypersthene), and feldspathoids (such as nepheline, sodalite, & leucite).
- Gabbro: Coarse-grained, intrusive/plutonic, & mafic cooled magma, containing the same minerals as basalt (only difference between basalt & gabbro is grain size due to difference in cooling rate).
- Diabase: Medium-grained, sub-volcanic, & mafic (in-between basalt & gabbro in regards to cooling rate, but composition is the same).
- Ryolite: Fine-grained, extrusive/volcanic, & felsic cooled lava, containing quartz and feldspar (such as sanidine, microcline, & plagioclase), with minor biotite and hornblende.
- Granite: Coarse-grained, intrusive/plutonic, & felsic cooled magma, which contains the same minerals as rhyolite (only difference between rhyolite & granite is grain size due to difference in cooling rate).
- Syenite: Coarse-grained, intrusive/plutonic, & intermediate (between felsic and mafic) cooled magma, containing similar minerals to granite, but nepheline instead of quartz.
- Andesite: Fine-grained, extrusive/volcanic, & intermediate cooled lava, containing plagioclase, biotite, hornblende & sometimes pyroxene.
- Diorite: Coarse-grained, instrusive/plutonic, & intermediate cooled magma, containing the same minerals as andesite (only difference between andesite & diorite is grain size due to difference in cooling rate).
- Dacite: Fine-grained, extrusive/plutonic & intermediate cooled lava, very similar to andesite, but slightly more felsic, containing plagioclase, augite, sanidine, quartz, biotite, and hornblende.
- Peridotite: Coarse-grained, intrusive/plutonic, ultramafic cooled magma, containing granular olivine and pyroxene.
- Obsidian: Glassy, extrusive/volcanic, felsic cooled lava, dominated by silica.
- Pumice: Vesicular, glassy, extrusive/volcanis, felsic cooled lava, similar to obsidian, but cooled with air bubbles.
- Scoria: Vesicular, glassy, extrusive/volcanis, intermediate to mafic cooled lava, similar to pumice, but denser and sinks in water.
- Anorthosite: Coarse-grained, intrusive/plutonic cooled magma dominated by plagioclase, typically labradorite.
- Tuff: Consolidated ash (thus, extrusive/volcanic), and can be felsic to mafic.
References & Helpful Resources:
Essentials of Igneous & Metamorphic Petrology by Ronald and Carol Frost: amzn.to/37Zs9AL
Thin Section Rotation Website: www.virtualmicroscope.org/col... (just pick a collection, pick a rock sample, and it will show you hand sample pictures, thin sections, and tell you the mineral assemblage)
Thin Section Atlas (in color): amzn.to/3HYsrrj
Online Metamorphic Mineral Thin section Atlas: www.earth.ox.ac.uk/~oesis/atl...
Earth Materials by Cornelis Klein and Anthony Philpotts: amzn.to/3z5sCxe
GEO GIRL Website: 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!)
Studying for an exam? Schedule Tutoring with me: GEOGIRLTutoring.as.me/
Directly offset your carbon footprint with Wren: shrsl.com/3d0t2
Non-textbook books I recommend:
Oxygen by D. Canfield: amzn.to/3gffbCL
Brief history of Earth by A. Knoll: amzn.to/3w3hC1I
Life on young planet by A. Knoll: amzn.to/2RBMpny
Some assembly required by N. Shubin: amzn.to/3w1Ezm2
Your inner fish by N. Shubin: amzn.to/3cpw3Wb
Oxygen by N. Lane: amzn.to/3z4FgwZ
Alien Oceans by K. Hand: amzn.to/3clMx1l
Life's Engines: amzn.to/3w1Nhke
Tools I use as a geologist/teacher/student:
Geology field notebook: amzn.to/3lb6dJf
Geology rock hammer: amzn.to/3DZw8MA
Geological hand lens: amzn.to/3jXysM5
Camera: amzn.to/3l6fGRT
Carbon-neutral pencil bag: shrsl.com/3cvjv
Carbon-neutral backpack: shrsl.com/3cvkc
0:00 Basalt
6:01 Gabbro
8:36 Diabase/Dolerite
9:28 Rhyolite
13:03 Granite
16:11 Syenite
18:01 Andesite
19:49 Diorite
21:38 Dacite & Granodiorite
22:32 Peridotite
24:05 Obsidian
25:07 Pumice
26:06 Scoria
27:24 Anorthosite
28:47 Tuff
29:55 Related Videos & References
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