Rock Identification with Willsey: Volcanic Rocks (Tuff, Obsidian, Pumice)

Dive into these distinctive and interesting volcanic rocks with geology professor Shawn Willsey. Learn how to identify tuff, obsidian, and pumice, and, more importantly, the story behind the rocks.
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Shawn Willsey
College of Southern Idaho
315 Falls Avenue
Twin Falls, ID 83303
Link to PDF of document: drive.google.com/drive/folder...

[@jscottmaclean226]

I had no idea Pumice & Obsidian were the same material. I LOVE your Pumpkin Obsidian sample, almost doesn't look real. I really enjoy your channel, keep up the great work!

[@LouisTroyAustin28]

Yah you can easily make pumice from obsidian by melting when not under pressure and letting it cool

[@Bri_Bri_the_Wise_Guy]

"The wonderful world of sedimentary rocks" I love it, can hardly wait,

[@w4lauppe]

31:20 wow devitrified obsidian (my rock vocabulary grows). Thanks for another amazing video.

[@flakesinyershoe8137]

Flintknapping is what got me hooked on geology. It was harmless at first, a usgs report here, a usgs report there.. I only planned on using it to locate good chert sources... now I want to know things like the geologic processes involved in the formation of geodes in the local mississippian sedimentary formation and how the chaotic slumping (i think) exposed in the road cuts came to be. Boring sedimentary stuff. Thanks for filling some gaps in the obsidian story! I was unaware volcanic ash was so gnarly.

[@davidk7324]

Helpful analogy for the pumice/obsidian.

[@farmermark2067]

Who uses or has used "Lava" hand soap with pumice? Have not used it in a while but now want to get some lol. Thanks Shawn, enjoying your vids!

[@shawnwillsey]

The corner of the package read, "Pumice Powered!"

[@missingremote4388]

Some kitty-litter comes from pumice mines. In California. I've visited the mines . It's near Fossil Falls, on Owens river ( unknowingly my airfilter was not on my engine. But my trucks still works) lol

[@dustytrayl]

Thank you for the root beer! I shall always remember now! Great analogy!

[@shawnwillsey]

You bet!

[@deltalima6703]

Guinness

[@Yetibiker67]

Thank you Shawn for the lesson. Really appreciate all your efforts. Glad to see your subscriber list growing.

[@Rachel.4644]

Gosh I really appreciate your classes about rock identification, focusing mostly on rocks we will see in the "wild." I have learned a lot! Still not super confident I've correctly id'd the rocks I've hauled home....but maybe....! 😁👌🏼

[@shawnwillsey]

Just takes practice and seeing lots of rocks. More important is interpreting the rock's story.

[@Rachel.4644]

@@shawnwillsey You're right! That is a big missing chunk of my learning. Thank you.

[@shawnwillsey]

You can support my field videos by going here. Thanks! www.paypal.com/donate/?hosted_button_id=EWUSLG3GBS5W8

[@sdmike1141]

Obsidian…sneaky cool!! Thanks

[@holly50575]

Wow! Thank you! You just answered so many questions I have had for decades, I am so grateful.

[@shawnwillsey]

Glad it was helpful!

[@tiffanyannhowe1712]

Thanks for the vid drop 😊

[@chucklearnslithics3751]

Outstanding! I have been waiting for this episode... It didn't disappoint!

[@MountainFisher]

I remember hiking near Devil's Postpile over a few miles of greyish white pumice. The way it crunched was irritating like fingernails on a chalkboard way. The whole area was covered by a pyroclastic type flow, by then broken down, but plenty of plum sized pumice. Obsidian Dome in California is full of that first piece of obsidian with the snowflake effect. I couldn't find a piece of it without it. A whole big hill of the stuff. I recognize that as Bishop Tuff, that light color gives it away. I used to live there. Are you familiar with the Gila Caldera Tuff of Southern New Mexico Shawn? It is a little more brownish than the Bishop Tuff. There is a road cutout on route 52 where right in the middle of the tuff is a car sized boulder of milky quartz tossed there millions of years ago.

[@minnafinland1660]

Very good series for me... Thank You, Shawn!

[@jeaniechampagne8831]

From here I went straight to the history of pavements and the reason I did, was that your rocks reminded me of the pavement - street in front of our house growing up. The streets were paved with a rock layer then the black layer to smooth it out. Afterwards we had all these rocks on the side of the street that we played with and cracked them open to find all kinds of pretty stuff. Maybe everyone already knows this, about rock pavenents. This was way back in the 50's. Great video. Time well spent. I love rocks!

[@jdean1851]

VERY KOOL" Thanx for posting!

[@shawnwillsey]

You bet

[@loisrossi841]

Thank you.

[@nitawynn9538]

Thank you. I found obsidian and pumice fascinating. 😁

[@oscarmedina1303]

Thank you Shawn. Very helpful presentation. I have a much better understanding of the three types of rock materials after watching your video.

[@one44east77]

Thanks for a great video. Interesting and informative.

[@cinderelly2592]

Awesome

[@caspervegas3288]

Love the information very intelligent

[@RichardFreeberg]

Thanks! I really enjoy your mini lectures. Entertaining and edifying.

[@Meggligee]

Thanks for covering my favorite volcanic product, obsidian. I thoroughly appreciate the explanation on the devitricication of obsidian and snowflake obsidian. I originally thought my samples were dirty but after cleaning, the same white crystals you’re showing on these pieces show up on my samples also. If there are crystals, what age does that signify the obsidian is or range?

[@NNn-lt1rf]

You need to visit Maona Loa. Soon.

[@pmm1044]

Thanks for tuft info. Went to smith Rocks and saw the hard and dense pink rhyolitic tuft and the soft pyroclastic flow tuft.

[@stevewhalen6973]

Thanks!

[@shawnwillsey]

Thank you!

[@broadcastmyballs]

Excellent video I learned a lot from. I'm glad you showed and explained volcanic ash, I have never seen it before in person so I never knew its texture. Does pumice devitrtify as obsidian does? Would that account for the opacity and frangibility of some pumice relative to others?

[@shawnwillsey]

Yes, both glassy rocks devitrify over time as molecules slowly migrate and form small crystals.

[@directcoolingservice7225]

Jewelers loop amigo

[@murarirajagopalan3771]

Kudos to a nice presentation. You might consider a value -add by showing the rocks first followed by thin section display to identify the minerals and maybe even a chemical composition analysis. You can plan paid sessions too for Value-adds!

[@c1s1125]

@shawnwillsey I have obsidian limbcasts from the VV. Too bad you don't discuss opal in any of your videos. Your channel would blow up if you made a few videos about opals. You've already got plenty of Yellowstone keywords. Thanks for your content!

[@shawnwillsey]

You bet. This series is on rocks and opal is considered a mineraloid, but I agree it would be a good topic. I wrote a whole chapter on the opal deposits of Spencer, ID in my book, Geology Underfoot in Southern Idaho.

[@tinymetaltrees]

I am astonished that I have never heard of devitrification before! I wonder which other materials are the final results since they must ordinarily go unrecognized after having undergone this metamorphosis.

[@WaylonFoxtrot]

Idaho, you say? It's a petrified potato! 😂

[@padraicmurphy6045]

Particularly interesting rock vid. Had no idea pumice was a glass. Does pumice devitrify as well or does the foamy structure prevent crystals from forming?

[@shawnwillsey]

Yes, pumice is prone to devitrification also.

[@haroldtanner9600]

Ash from Mt. St. Helens destroyed many vehicle engines and also damaged the jet engines on aircraft that flew through the ash cloud enroute to SEATAC during the St. Helens’ eruptions in 1980. More recently the routing of trans-Atlantic flights was affected for a period of time during the eruption of volcanoes on Iceland.

[@3xHermes]

👍

[@rodbhar6522]

Never knew that Obsidian was young rock. I’ve been hoping to find some locally amongst the 600 million year old basalt where I live. 😂

[@cecinit2007xyzzy]

Lots of rock identified to me as ash in Galapagos. Should mostly be pretty mafic rock (hot spot somewhat like Hawaii) - even a green sand beach (or several) there

[@haroldtanner9600]

You weigh equal volumes of the tuff samples to compare density? It seems that the rock from the bottom of the gorge should be more dense.

[@alicemiller3139]

General question. I hear the term country rock. I live in NC now but used to live in NJ and still go back. I see a lot of shale and wonder if that is our country rock formations in all the states out east. Can you explain exactly what country rock is? Thanks!

[@shawnwillsey]

Country rock is a broad term referring to the dominant rock in a region, often one that has been intruded by magma or mineralized.

[@grizzlymartin1]

Glad I found your channel. “Oh, this is the neighborhood I’m in.“ Question, as a recent hobbyist into all things geology, one of my first main goals (like you say) is to “know the story.” In other words, I want to be able to go out into the hinterlands and begin to familiarize myself with my geological friends all around me. I’m wondering if you can do a program devoted to the very first steps of knowing where to begin to understand the story of “What neighborhood I am in” - no matter where on earth I am dropped? I live in the Rockies, so I quickly see all around me a lot of sedimentary structure with a lot of upheaval metamorphic rock formations. And the majesty of much of it is that it can change so dramatically in such a short time or distance. So that is my question really is - where does a person like me begin, matter where they dropped on the face of the Earth, to look around and say “Oh, this is the neighborhood I’m in.“

[@shawnwillsey]

Welcome aboard and thanks for subscribing. Your suggestion is a good one. I've got a few ideas on that front. I supposed the first video in the Rock ID with Willsey series would help too as I cover how to tell groups of rock apart. Stay tuned and hopefully I can address this soon.

[@grizzlymartin1]

@@shawnwillsey do you have a link for this show you reference? Thank you.

[@grizzlymartin1]

Just went and looked. I see several rock ID videos and series. I guess this is what you’re referring to. Thanks.

[@shawnwillsey]

@@grizzlymartin1 kzbin.info/www/bejne/gWqulJSlmJ10ZrM

[@grizzlymartin1]

Have you put out any kind of syllabus online that someone like me can download and follow.?

[@jeffrysmith8200]

When obsidian denitrifies are the crystals that form quartz or some sort of xeolite or?

[@shawnwillsey]

cristobalite, a type of quartz.

[@madman9333]

What is the rock called that (I’m guessing) forms inside of trees that are (petrified/vulcanized/vitrified/fossilized???) where I suppose water/sand ??? Is trapped in the tree when a pyroclastic flow ??? occurs?? I have some big chunks of it and pictures of it in veins of what was definitively a tree found in the same area around Mono Lake

[@shawnwillsey]

Most wood is replaced by various forms of silica (quartz). Small impurities yield various colors.

[@Rockhoundingcolorado]

You forgot Scoria?

[@shawnwillsey]

I believed this was covered in basalt episode since scoria is a type of basalt.

[@mauricerieffel5627]

Thanks!

[@shawnwillsey]

Welcome! Thanks for your support.