How to Identify Igneous Rocks in Thin Section & Hand Sample | GEO GIRL
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- Опубліковано 9 лип 2024
- 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
Disclaimer: Links included in this description might be affiliate links. If you purchase a product or service with these links I may receive a small commission, but there is no additional charge to you! Thank you for supporting my channel! - Наука та технологія
I didn't know pumice was glassy! The KFC restaurant near my house has landscaping with what my son called "red pumice" (for the red and white color scheme) now we know it's called scoria and it sinks in water.
GeoGirl is a scientist and a wonderful peer who shares the best of Earth Science. I am sure that she inspires the next generation of geoscientists.
This one is going into my quick reference Playlist.
Great video! I’m mostly a hand-sample kind of geologist, so I’m always excited to see optical mineralogy content.
6:26 - “The oceanic crust is made largely of gabbro.” HOORAY!!! I’ve seen and heard so many people say the oceanic crust is made of basalt, that it’s become a pet peeve of mine. (The ocean FLOOR is basalt.) So I’m SO HAPPY when someone gets it right! 😁😁
Yay! I am so glad I said that then hahaha! I was actually unsure at first when I read that because I thought to myself, "I thought it was basalt..." LOL So clearly, I have been taught that as well. But thankfully, after I read at depth part, I was like ok that actually makes complete sense haha
@@GEOGIRL please expand
انا طالب علم الجيولوجيا وعندي اختبار بصريات صخور و الحمدلله اني لقيت قناتك ❤
اتمنى ان لا تتوقفي عن النشر، استمر 👍
I'm a geology undergrad in my senior year, my professor told me to look at pictures to identify glass in a thin section for research I'm doing for him. Glad I found your channel!
So glad you found this video helpful! Best of luck with your research! :D
I wish this channel was available when I was at University. Really good videos and nice for refreshing one's memory on certain topics.
I love Syenites. They are like the doorstep to both alkaline and calc-alkaline worlds.
I truly love all of your videos Rachel! I’m almost done with my Gemology courses and have fallen in love with petrology and geology in the process. Working my way backwards you might say. All the topics are related anyways lol! Your videos are extremely helpful and informative! I can’t get enough!
Excellent, very informative video! Thanks!
Great overview! Thanks for the video!
Such a great video!👏🏽👏🏽
Too late!, my igneous thin section pracs went okayish :(
Thanks for making awesome content, helped me a lot
Oh darn, I should've posted it sooner! Well I am sure you did great, and I hope you can use this video for a future exam if you have another ;)
I am working now on an Earth Cache and your videos are a great resource, thanks!
Old forgotten knowledge from half a century ago. Thanks for the reminder!
Great content as always!
My geology is nothing without your video....
Iam Indian...I can understand little English...but.. I like and love your video....,😇😇👌👌👌🍻🍻
So glad you enjoy my videos! ;)
@@GEOGIRL most welcome...D😊😊💖
It would have been so nice to have these videos back in my undergraduate days...haha
Great video!
Great information. Thanks for sharing.
Good info' , many a doubt has just been answered. This is the way to truly unďerstand and recognise rocks.
You are my saviour 😂🙌🏽. It gets more better as i watch more of your videos. Thank you for all these knowledge!
Thank so much! I am so glad you have found these thin section videos helpful ;D
@@GEOGIRL I took a test today and it was a success and its really all thanks to your videos. I was able to identify Plagioclase feldspar and Olivine, and ofcourse Quartz too 😅, and then i gave explanation about Birefringence and Pleochroism, and some other talks too. Thank you so much for these videos!
@@lawarlkila YESSS!!! SO happy to hear that, great job!! And congrats! :D
I watched a guy (Shawn Willsey geo professor) talk about the rocks we see in the mountains and I think he was saying that tuff was the super-heated ash or pyroclastic flow from a volcano. its a pretty loose material until it butts up to a layer of basalt where the tuff layer is fused together like concrete from the heat of the basalt.
Very interesting. I typically just classify rocks into two basic categories aurum and leaverite. Sometimes I exclude from leaverite certain minerals such as hematite, arsenopyrite, and quartz.
If you want, I can send you some non-aurum samples of these rocks from the bottom of the Bering Sea, they come from a glacial alluvial thrust zone nearshore of Nome, Alaska.
Super interesting. Sanidine was a new one for me, I always wondered where the red colouring of Rhyolite rock came from. I had thought perhaps Iron oxide though Iron is on the mafic side and did not seem likely in Felsic rock.
Thank you for sharing! I'm going rock hunting now! Keep the videos coming!
Oh so fun! Good luck, I hope you find some good ones ;D
I have already gotten enough, trying to decipher the type of fossils and symbols on them. Do you have any videos on symbols?
Thank you so much ma'am ! 🤗 I was struggling with igneous slides , now I can observe , identify & write about hand specimens & thin sections in my practical exam . You've helped me alot during my examinations ! 💗 I wish I could have your brain during my exams 😬😂 Lol !
Wow, this comment made my day! I remember being in the same position as you! I was taking that class and could not identify ANYTHING in thin section, so I am very glad that this video is now helping people like you identify these minerals and rocks and pass that class!! ;D Best of luck !
Great channel. Don't know why UA-cam hid it from me for so long!😁 I'm not a geologist, just a fan, but my gf is, which definitely played a part in our coupling 😅🤣😂😁
You rock!
My friends hate on me for collecting rocks.
I went to Naples Italy for my birthday once and brought back rocks from the summit of vesuvio for them and they laughed.
Don't listen to them! Rocks are so freaking cool!! Each and every one tells a story ;D
Good video! Just curious, have you watched Prof. Nick Zentner of Central Washington University? (Nick on the Rocks). He might be a good reference as your site grows. Thank you
Loved this video Rachel! My thesis at UC Davis was a mapping project in the eastern Sierra Nevada. Igneous lithologies dominated and I thrilled in making my own thins sections and describing their optical properties. I dearly miss having access to a petrographic microscope and have considered buying a used one just to remain connected. On another note a question. All of us originally got into geology because we loved the field and the natural world. Would it be possible to present a video on how geologists conduct basic work in the field? Brunton compass, hand lens, sampling, mapping contacts, measuring section, etc..etc. It’s so much a part of many of our lives. It might be a challenging video to do, but I think the public would find it interesting.
I would love to and plan to make a video or videos in the future showing how we conduct simple field measurements and use these tools and such, but I am waiting for a time when I can get to the field and have someone to help me film and stuff. Hopefully I can take a trip sometime soon to do so! ;D
Yes, I know, going from lecture style to onsite filming is a whole new and challenging format. With limited time and logistical support (put some of those undergrad geology students to work as cameramen/women!) it may not be feasible now…but, when you can, I’m sure such videos would enhance, all the more, what is presently a truly unique and awesome channel.
I finally got around to watching this last night actually. I remember you asked "what's your favorite Igneous rock?" I couldn't answer it of course. My quick answer last night would have been scoria. That looks like the classic lava rock you see, with all the holes in it. But, there was also the obsidian.
The obsidian is almost more obvious than the other rocks here; but, there is something more interesting than just the fact it's a bit more shinier than the other rocks. There's a suggestion that stone age people used them for mirrors!
But, after re-watching this a bit, I think I'll go with the Peridotite! It's interesting that maybe they were more common a long time ago, before the crust formed.
Just a day after mentioning that neolithic people had a fascination with obsidian, Physorg comes out with an article about this fascination(what little can be said; they collected it and shared them around!)
The article title is "New analysis of obsidian blades reveals dynamic Neolithic social networks" If you want to read it. It doesn't say much other than early agricultural people took to obsidian!
To see Syenite all you have to do is go to a bank. The counters and some of the walls are covert with it. Most of the time it comes from Spain. It's called Carmen Red Granite. But you and I know is not a granite.👍
A suggestion - you seem to use the word 'clasts' in the place of 'laths'. 'Clasts' is a terminology used in sedimentary petrology. Also while speaking of basalts, it may be useful to add that olivine and quartz generally do not go together.
Wow thank you very intelectual And clear explanation
You are very welcome! So glad you enjoyed it :)
also, i visited easter island and as i recall the famous moai statues were carved out of tuff. the quarry is along the side of volcano rano raraku.
Excellent videos
Thank you!
That graphic you used of igneous rock composition. Is that available anywhere? Its a good one.
Wish I had this last semester
I would love to have videos fo amateurs. What is this stone I found? How can I differentiate feldspar from quartz etc
Is tuff ever considered a sedimentary rock? My understanding is that it turns into rock just like other sedimentary rocks, it's just that the source clasts are volcanic. Am I missing something or is that just the way the classification is done?
HI, have you already made a video on mylonite and tectonite in thin section? Please, I am really interested!
What's your thoughts on pegmatite formation?
any reason why the mica or pyroxene in quartz is often rectangular shaped? i notice that a lot in hand samples, it seems to be distinctive.
Absolutely! It is based on their atomic arrangement. That's also the reason that mica is 'platy', it's atoms are arranged in sheets, so that's how it breaks (along the bonds since it can't break along the atoms). What a great question, thanks for bringing this up! ;D
excellent video! congratulations! my cat's name is dacite greetings from Bolivia!
Can you also add links to previous videos below. Saves having to go back seaching for them in the vid.
Can you recommend a good lexicon for someone new to Geology? I'm finding my normal method applying latin roots and ancient Greek mythology isn't working as well as it usually does?
I’m not an expert but it seems like a lot of rocks are named after places (e.g. andesite after the Andes Mountains).
Why is the grandiorite even lighter in color than dacite (in the rock photos you have shown)?
Well it only appears lighter overall because it is a coarse-grained rock instead of fine-grained, so the lighter parts are lighter and the darker parts are darker because they are single grains, whereas in the fine-grained dacite the colors combine in appearance because the grains are much smaller. Also, remember that these rocks represent a range of silica % not a singular value, so sometimes they're colors can vary even though they still lie within the silica % range for that classification :)
❤
Oh, oh, Teacher Geo Girl! **raises hand** I have a question about that igneous rock composition diagram! I'm familiar with the Bowen's Reaction Series, with the series ending with orthoclase feldspar, then muscovite, and lastly quartz crystalizing at low temperatures. But the mineral composition diagram shows orthoclase appearing and becoming more abundant only in higher percentages of SiO2 than quartz. Everything else between the two diagrams are in line, so why does this discrepancy exist? (I'm sorry it's not actually a question about thin slides!)
HOLY COW! That's is a good observation, I've never noticed that but you're right! I have no clue lol I would've assumed the diagram followed the reaction series exactly... I guess since it's mineral volume % plotted against silica % (rather than temperature & silica % like bowens reaction series), even though they cover a very similar range of silica % (felsic- ~60-70%) and clearly have similar formation requirements, orthoclase may be greater in volume percent in such felsic rocks (which brings it up the volume % y-axis of the composition diagram, but wouldn't affect it's silica % range or it's position in bowen's reaction series). What do you think?
You gotta do one for sedimentary rocks if you haven't! :)
Yes! I plan to show a lot more sedimentary thin sections in my upcoming carbonate petrology playlist ;D
@@GEOGIRL awesome! I’m excited!
I’m taking sed/strat right now in school!
@@martya1038 Best of luck!
By the by kid, if you can show how to positively identify the big 5, gold, silver, copper, lead, and platinum with your microscope, you can get a million hits, just posting to prospecting forums ;)
I thought orthoclase was the common K -felsdspar in granits
You make me want to study geology. I had no idea about any of this. Can you do a video on clay? I have pure white and orange/red clay seams and trying to find information- I read that clay is held together by a chemical bond. But what bond? Why? How? What the hell is clay 😭
Oh what great questions! Clay is actually defined by grain size rather than composition (it's the finest/smallest grain size), and it typically forms by the weathering of silicate minerals, such as feldspars, but I realize that has no meaning to someone that isn't a geologist haha. If you want to see more about how clay forms via weathering, see this video: ua-cam.com/video/V6nWMzYxsUM/v-deo.html, specifically at about 19:10, and if you want to see more about how clay/mud is defined by grain size, see this video: ua-cam.com/video/hTkAW6iJY94/v-deo.html. I actually don't have a video discussing clay specifically and answering these questions directly, so I will certainly make one in the future! Thanks for the suggestion ;D
Edit: I forgot, I also have a video about crystal structures and the bond types common in minerals: ua-cam.com/video/GWr75KAbSas/v-deo.html, but this video is a very detailed crystallography lecture, so I wil certainly talk about the bonds again in the future video about clays in a way that hopefully simplifies things and brings all this information together to make sense. ;)
@@GEOGIRL thanks for such a detailed answer! I dig up fossils from the clay and honestly it does my head in. Does clay eat the rocks? Are the rocks melting into clay? What is going on here 😂😭💖
I definitely will be watching each link you sent. Very very much appreciated!! Omg how exciting! Thank you soooooo much!
@@KerriEverlasting Hahaha I would say you're not far off with 'rocks melting into clay'! ;)
@@GEOGIRL where is part 2 of the microbial dissolution video?
@@KerriEverlasting Sorry I wasn't great at video titles back then (still not great haha), but here's the part 2: ua-cam.com/video/kkEl8_04QHM/v-deo.html
This link will take you to the geobiology playlist which will also provide you the rest of the videos in the order they are intended to be watched ;) Hope you enjoy!
wow yr rly smart o_o
Aw, thanks! But it's more so that my references are really smart and I am getting better at relaying information haha ;)
Some videos in your playlist can't play...
Which country you are
Hii..geo girl...
You do look very similar to my college crush 😇
0:47
what is your linkedin profile? geologist there should see your videos. they are good
www.linkedin.com/in/rachel-phillips-3436a4146/ There you go! Thank you! So glad you like my videos ;)
You are beautiful 😍 and i really like you by physical
Do you still play golf?🤔
Haha yes, sometimes, but not for an official team anymore. How'd you know I played golf?
@@GEOGIRL So I am a new subscriber and I've been working my way through the early videos...and one of them had a comment from your mother, clicked on her and then found out about your golf swing! 😁
Haha Wow, you really went back far! Well, yes, I played as an undergraduate for the UT Arlington team, but these days, I play maybe once or twice a year haha. What about you? Do you play?
@@GEOGIRL I do, but not at your level...I think I might try and copy your swing...very efficient! I'm better at rock climbing...which is my angle for learning a bit more about geology.
@@aboukirman3508 Ah I see! I have never been rock climbing but think it would be so fun!! Maybe someday I'll get to go ;D
en.wikipedia.org/wiki/Broca%27s_area Broca's area