Rock Identification with Willsey: Volcanic Rocks (andesite, dacite, rhyolite)

Learn to identify and describe andesite, dacite, and rhyolite (three common volcanic rocks) with geology professor Shawn Willsey. Part of my ongoing series on some easy and practical ways to identify and interpret rocks.
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[@nitawynn9538]

I’m told that Stone Mountain in Georgia was a pluton underground. Now a lot of it is exposed with more still below ground. So cool!

[@w4lauppe]

Great informative series of rock lectures. Keep them coming.. Thanks

[@MrFmiller]

Another outstanding video. You keep putting them out and I keep learning.

[@shawnwillsey]

Win -win.

[@roneldridge7991]

I’m chasing porphyritic dikes in my area for gold and Rhyolite in cascades for cool rocks , and I found my first tourmaline samples hiking east of cottage Grove in Andesite . A tremendous amount of work trying to identify them, this is definitely the best and less complicated way of explaining it.

[@owendigity1581]

Don't tell people what you know. College "geologists" are just hoping to find an "arrowhead".

[@remorrey]

Really appreciate your videos. At 76 I'm still able to learn about the rocks we had in Southern Utah. Thank you.

[@MountainFisher]

Interesting presentation Shawn. I used to live in Mammoth and Bishop for a couple of years and all kinds of volcanic rocks I didn't know the names of and now I do.

[@stevengeorge5605]

Thank you, Shawn!

[@macking104]

one reason knowing rocks is important “On San Miguel Island, rocks dating 50-30 million years ago contain well-rounded pieces of rhyolite that are chemically identical to the rhyolite found in similar age deposits in San Diego county. The inference is that these pieces of rhyolite reached the islands in a submarine fan deposit when the islands were positioned off the coast of San Diego. Analysis of the direction of the currents flowing at that time shows that they came from a southerly direction. However, the only possible source of these sediments is from the mainland, which lies to the east of the islands, giving geologists one more reason to believe that the islands have rotated 90-100 degrees in the last 20 million years.” (nps channel islands)

[@stevenwolfson8699]

Thanks so much for putting these videos together! Great way to help folks at least being to differentiate the more subtle differences in rock groups.

[@BP_in_OR]

There's some dark-toned Dacite up in the Cascades near where I live and it looks similar to the andesites you show in the vid except for the vague, faint purplish hue it has.

[@leslie3832]

Thank you, Shawn, once again. I am having trouble remembering the names so I created this pneumonic: Red Dogs Are Buffalo For Ryolite Dacite, Andesite Basalt Still working on one for Granite, Granodiorite, Diorite, Gabbro Maybe Giant Giraffes Dig Gabbros! Haha

[@stevebrooks1355]

Thanks Shawn Started watching your vids when you did Bonneville Floods and area- always fun and informative I appreciate your joy at bringing info to us--- keep expanding my vocabulary 😀 I dig this rock shyte

[@Rachel.4644]

Yay team! Terrific class that I must watch again to ... I hope... remember. Love the samples. Thank you Shawn!

[@Smiley_ASMR]

These are SO helpful for the igneous section of my petrology class!! I can look at charts and rocks all day but having you go through a few variations of each type and ways you can identify them is so so so necessary for me to remember it!!!! Thank you thank you thank you!

[@nitahill6951]

Understanding how porphyry works has been a problem for me. I think your identification was extremely useful. You make things very understandable.

[@davidk7324]

Thanks Shawn, great info. These are great companions to your field videos. Maybe link these to field videos where indicated.

[@markthomas4083]

Solid info, clear and quick presentation.

[@grandparocky]

very much enjoying your series. Best rock ID videos I have seen!

[@shawnwillsey]

Wow, thanks!

[@PlayNowWorkLater]

This is such a great series! So helpful.

[@shawnwillsey]

Glad you think so!

[@abelables]

Cool info and video in general! But we use crystallized and cooling in intrusive and extrusive respectively. Magma are crystallized when it’s underneath and forming Intrusive, then Lava are cooled to formed Extrusive rocks.

[@safiaamimi230]

Amazing, thank you so much sir.

[@sartgems6981]

I'm a following you channel about rock..thanks for knowledge brother

[@shawnwillsey]

Welcome aboard!

[@manjunathaluru2157]

Good explanation 🙏

[@jadem.escarlan4294]

Thanks for explanation sir.!!!

[@CricketsMa]

Seriously cool!

[@graemedevine9651]

Very interesting indeed, thank you

[@user-id3to6gt2l]

So helpful.. thank you keep going ❤

[@rogercotman1314]

WOW, what an informative educational video ............. thanks Shawn ................... 153 like .......................

[@briane173]

Bada-BOOM! Ugh, how I wish I'd started studying geology earlier when I still had a functioning brain. SO hard for me to retain all the different minerals and associated names with rock types. I'm hoping that as the technology progresses I'll be able to make better use of Google Lens to ID rock types in the field without resorting to carrying mag-glass and acid with me. I'll probably never get away without a rock hammer but it'd be nice to get a reliable interpretation of rock type through Google Lens as we move forward in time. My brain is too feeble to commit all this to memory. It would be absolutely impossible to determine ages outside of a lab; but if we have a rudimentary understanding of the geology and geography of the area from which we're taking rock samples it's easier to deduce their origin and along with it, their approximate age.

[@shawnwillsey]

I've got just the thing planned for you soon. A way to determine rock types and ages in your area before you go out on your adventures. Stay tuned!

[@stevekolstad4445]

hi Shawn I live in Meridian and I am trying to figure out the different between Rhyolite and Basalt. The Boise foothills have a lot of Basalt looking ( very dark and very fine with very small minerals visible ) The basalt lava flows we have near lucky peak with the columns that climbers love and basalt with bubbles and basalt without bubbles. This is very obviously basalt. Now the rocks that pop out of the foothills especially just above Boise are also very dark black to brown. Some maps call this Rhyolite. I know some basalt is dike like but can you have a dike that does not reach the surface until the hills are eroded away and not intruding in any rock. I have seen the dike swarms to the south of highway 17 between Garden valley and Lowman. The rocks in rocky canyon road and first foothills even those below tablerock look very similar. The weathered Idaho Bath that you see just above Lucky peak dam have similar look. The roadcut on highway 21 near the lucky peak dam shows white looking granodiorite ( some even breaks easily into white sand ) and when weathered as found just before the roadcut looks dark too. I got a sample of the rock at rocky canyon and it is black basalt looking and not granite or Granodiorite . I have samples of rock that fits Dacite and Andesite definitions but i an not sure where i got them. Thanks. Do you spend much time at the Idaho Museum of Mining and Geology? I noticed you are one of founding members.

[@philsigman9088]

Thanks Shawn! Just started following you a week ago and your videos have me researching information about my area here in Emmett, more specifically the Big and Little Buttes. Found out they are mostly made up of Columbia River basalts. I'm guessing they got here through fissures?

[@shawnwillsey]

Yes, fissures that opened up in far eastern OR fed large volume flows that covered western ID and big chunks of OR and WA.

[@ThapeloJustice]

Thank you sir

[@stevewhalen6973]

Thanks!

[@abbyh8678]

Awwww it's just a piece of schist.....🤣sorry....east coast early, NO COFFEE MORNING.....cool program, thx

[@abbyh8678]

I live in Madison NH....a stones throw from the Ossipee ring dike.....see all kinds of volcanic, plutonic rocks here.... geology here in NH is really cool....pretty complex

[@shawnwillsey]

NH is gorgeous. Visited once many years ago. White Mtns. Chocura. Very pretty.

[@abbyh8678]

@@shawnwillsey AMAZING mining up here....columned basalt, ponds that are actually ancient volcanic necks?? SO COOL🤣 geology......ROCKS......SORRY NOT SORRY🤣 Chocoroa is great....spent many nights up in the cabin up there

[@yakaronielyak8299]

as someone interested in baja geology -Located in San Diego and travel there from time to time. Do you have any further information on dike systems in Baja from your work down there? Thank you for great video.

[@shawnwillsey]

Holy cow. Taking me back a few years. I mainly mapped and researched area just west of Loreto in the Sierra de la Giganta. Dike systems there are mostly andesitic. What questions do you have?

[@yakaronielyak8299]

@@shawnwillsey Shawn: I'm interested in the granitic pegmatites that formed at crystal developing pressures. I have spent many hours walking baren pegs and any information I can get that can focus my efforts is greatly appreciated. Rescuing crystals from the destructive forces that created them is my hobby. I have great respect for folks that have greater knowledge than me.

[@Meteorite-CaliforniumIron]

Nice

[@richardwest9054]

Have you done a video on the geologist's tools, both field tools and lab tools?

[@shawnwillsey]

not yet

[@richardwest9054]

just a thought. Thanks!@@shawnwillsey

[@stellarsunny]

What are the black grains in Andesite made of? You said Pyroxene: Augite, but I am always confused whether the black grains are Augite or Hornblende.

[@shawnwillsey]

In andesite, hornblende is more common. It forms elongated crystals, needles or rectangles, due to its cleavage plane angle. Augite is more boxy or square.

[@ituzzip]

What exactly is the time scale needed for crystals to form in molten rock? Basalt flows can take decades to cool without becoming gabbro, so it seems it would take hundreds or thousands of years for intrusive igneous rocks to crystallize. But if that’s the case I can’t figure out how small crystals might have managed to form in tuff, when volcanic ash covers such a wide land area and is porous so you would think it would be cool in a short time.

[@lauram9478]

❤

[@3xHermes]

👍

[@Barley150]

Why did they name that old mining town in Nevada Rhyolite? Is it a commercially valuable mineral?

[@hunnybunnysheavymetalmusic6542]

If some unknown people in California had not destroyed all 126 of my credits with the stroke of a pen, I would be in a geology class right now. So now I am hoping to find another way to identify all the rocks on my land and determine if I have anything of value here worth mining or if I just have the proverbial 'useless pile of rocks' with a few noxious weeds.

[@narendramakwana8429]

In which type of stone have gold?

[@zack_120]

15:33- quartz crystals aren't white color but grey instead?

[@tk423b]

Flashback to 1989

[@user-nz6im7wv8k]

Ajuda eu ...😢

[@user-nz6im7wv8k]

Boa tarde sou do Brasil eu presenciei um meteoro explodindo em SP inteiro a três anos atrás tenho bastante fragmentos desses aqui tenho provas suficiente não sei oq fazer help help sou seu fã tenho bastante fragmentos de diversos tamanho 😢 o que fazer eu do pra vc não quero dinheiro 💰 não só pra provar as pessoas ficam falando que estou doido mas sei que não estou eu só segui meus instinto estou recolhendo até hoje pedaços espalhando nas ruas do bairro aqui help 😢🎉

[@Rockhoundingcolorado]

Trying to identify a material used by a native american, it has huge cleavage, but not signs of conchoidal fracture. I think it may be rhyolite. Can I get you to check out some photos?

[@shawnwillsey]

Send me a good photo or two and I'll do my best

[@Rockhoundingcolorado]

@@shawnwillsey Lol, general delivery?

[@shawnwillsey]

@@Rockhoundingcolorado Email me 1-2 good photos. You can find my email under college directory.

[@Rockhoundingcolorado]

@@shawnwillsey oh ok.

[@hiker1658]

If Andesite is an extrusive rock, how do you get an "Andesite Dike"?

[@shawnwillsey]

Great question. The extrusive/intrusive classification is generally useful but somewhat arbitrary (like any classification system). You are correct that there are plenty of andesite, basalt, and rhyolite dikes. These are technically intrusions, but because they are so close to the surface, they cool quickly and thus retain many of the characteristics of an extrusive rock.

[@user-oz9et2jf3p]

Dating rocks 🪨 🎸 is the way to understand the world through general identity