Spectacularly Large Crystals in Black Hills Pegmatite: The Geologic Story
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- čas přidán 30. 11. 2023
- Check out the big crystals in this awesome roadcut with geology professor Shawn Willsey in the Black Hills of South Dakota. Learn how pegmatites form large crystals and explore the minerals found within. GPS location: 43.58931, -103.51043
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Shawn's bumper sticker reads "Caution: Geologist Driving -- Frequent Unplanned Stops"
Perfect!!!
I kept worrying you were going to forget about your hammer once I saw it on the ground! Thanks for a tour of this road cut from an uneducated but enthusiastic rock hound.
A buddy of mine did his undergraduate field geology in the black hills. He got to go to a pegmatite mine. He told me that the high wall of the mine had 30 feet long spodumene crystals in it. I have collected tourmaline in the black hills myself. Really a spectacular place.
I went to same place in 1980 it was way way way cool.
Now the last place he needs to visits is Northern Minnesota. Two rare rocks can be found there. Greenstone which is geothermal converted basalt and unakite which is the same kind of metamorphic granite. You won’t find both in most general rock books because of their rarity.
@@haseo8244 Actually, Unakite is metamorphosed charnakite, which is metamosphosed granite. Greenstone is all over the Blue Ridge of Virginia, particularly in the Shenondoah National Park. Unakite can be found in the foot hills of the Blue Ridge in Virginia north of the park. That is where I did my undergraduate field work.
That could've been me too in '78. Illinois St U did their field camp in the Black Hills. I have a huge spodumene though not 30'! Memory has faded a bit but I think it was called the Ada Mine
I visited those mines in the summer of 83 geoscienc field school. Samples i collected from the spoil piles are displayed in my library.
Im a lifetime resident of the Black Hills and im here because I've been fallowing this channel's coverage of Iceland's current Volcanic comotion. I would love to see our tourism industry shift from attracting wannabe bikers to our dangerous mountain roads, to attracting geologists and rock hounds to the relative safety of the ditches and hillsides beside them, lol.
From what I saw on this video I'm hoping to get over there soon! Looks like a rockhound paradise.
Some trivia: A "book" of mica is a single crystal! Black tourmaline crystals the size of hot dogs are abundant along the path to the Mount Rushmore sculptures not far from that first pegmatite discussed here. A famous crystal found in the early days in the Black Hills was a 12 meter long spodumene (lithium bearing) crystal. Pegmatites in Maine have feldspars 2 meters wide.
How many pounds is 12 meters?
ZERO@@daleolson3506
I've heard a lot about pegmatite, but never understood how it formed. Thank you for clearing up yet another geologic concept! And thank you for leaving the formation as you found it.
Love the roadcut. Having traveled across the USA several times, I've often wondered about the rocks I see. Your explanations and pointing out the different minerals was just what I needed. Thanks!
Love the Black Hills. Spent a lot of time there when Dad, Geologist, was stationed at Ellsworth AFB. Helped him survey for thesis. Collected quartz and mica.
My last visit to the Black Hills was when I met my older brother at Ellsworth to drive back to CA with him upon his discharge. The timing for the drive home was potentially disastrous. We left mere hours before a flash flood devastated Rapid City. This was June of 1972. We fully intended to stop at Rushmore but we were driving directly toward this mean storm system; we got caught up in ridiculously heavy rain in my brother's little Porsche roadster. We made it to Cheyenne by sunset, grabbed a room, and when I turned on the TV next morning the news was everywhere showing the devastating flash flood damage. We both turned white when we saw the restaurant we stopped at for lunch before leaving town _flattened,_ with a pile of cars stacked on top of it. There's no telling how many of my brother's friends may have lost their lives that night; but that memory is etched in my brain forever.
My brother's Porsche actually blew a fan belt maybe 20 miles out of town, and he had neither an extra belt nor the tools to replace it; he had to hitchhike back to Rapid City to pick up a new belt, and the guy who picked him up had the tools to put it on, but in the meantime I stayed with the car as I was watching this nasty storm approaching. I was shakin'. My brother got back _just_ in time to fix the belt and practically the minute we got back on the road the rain and wind and lightning started, and it didn't stop until we reached Cheyenne. What a day.
Found lots of good black tourmaline crystals in that pegmatite. Worked at Wind Cave NP a few times and I loved the geology of those Hills!
The comments are very often as interesting and enlightening as the videos. Well done everyone!
Took my kids to our sacred Pahasapa for their first time this summer. I was pulling over every couple of hundred feet because there is something cool at every turn. We got lots of nice muscovite specimens, as well as some nice quartz and black tourmaline crystals. The Black Hills and the surrounding area is a geological wonderland.
Yay! You are in the Hills! So glad that I chose to live here 8 years ago. Thanks for showing all that is just right there along the roadside.
Stunning roadcut, this is a fantastic channel for field geology.
Love it, one eye on the road one on the cutbank, my wife always tells me to watch the road more. Whats the fun in that. Thanks for taking the time to stop.
Fellow geologist here - I had a very similar experience screeching to a halt at one of these road cuts several years ago as a grad student. My poor brother who was in the car with me just about had a heart attack 😂 I actually did find a rock hammer there, so I was obviously not the first to stop. Collected some nice mica and what I thought at the time was hornblende, but I now realize must have been tourmaline! There were some beautiful folds in the schist where it contacted the pegmatite at that particular spot too. 43°41'47"N 103°36'19"W
Love the videos! I teach in central Utah, so your channel has been great for my students 🙂
12:44 - Wow, I've never seen tourmaline concentrated in a mass like that! I guess that's where a lot of Boron was concentrated in the melt.
😂 screeched to a halt...very familiar feeling...! And you KNOW what you're looking at while I usually don't. 😅 Oh my gosh, this is crazy rich with cool minerals! Oooh, tourmaline interior of the pegmatite dike! And sparkly schist (lots of that in the Cascades where I live)...! You do have a way of sharing your enthusiasm. 👏🏻❣️
Shawn, I'm confused about identifying tourmaline and hornblende. Any tips? Please.
@@Rachel.4644 Tourmaline is distinguished from biotite and hornblende by the absence of cleavage, and the presence of striated prisms (that Shawn mentions in the video).
Thank you, Shawn. I’m enjoying the tour. I hope my old brain can remember some of what you’re teaching.
2:52 love that first close up! What beautiful crystals!
I can't help it -- every time the Black Hills come up in discussion, "Rocky Raccoon" pops into my head and I hear it the rest of the day.
My husband just spent time in the Black Hills 5:16 on a vacation. Also in the Bad Lands. I didn't go because of a temporarily lame leg. 😊 He loved it there! We went together in 2010.
Very interesting info! Thanks for sharing. 😊
It’s just mind-bending that a geologist (Prof. Willsey) can pick up a rock and describe how it was formed from immensely powerful forces hundreds of millions of years ago. And it’s all just innocuously sitting there, by the road. I’ll never get used to geological time. 😮 On the truck, a new yellow sign: “Caution: Inquisitive Geologist on Board!” Haha.
The theme of the 2024 Tucson Gem and Mineral Show is "Pegmatites - Crystals Big and Beautiful". Dates are Feb 8-11 at the Tucson Convention Center.
I enjoyed this episode very much! TY for explaining it!
Question about crystals in Iceland: does the type of magma there form a lot of Olivine/Peridot? You mentioned the olivine in one of your last Roadcut videos that you recently uploaded and I've been doing some more learning about olivine [peridot] because it's so pretty! lol
Have a great week!
Olivine is common in many Icelandic lavas. Sometimes its big enough to see with naked eye, sometimes the crystals are too small.
Thanks Shawn for answering this. I (DavtheRockSlayer) asked a similar question on one of your Iceland videos and never heard back. No worries, I don't mean to suggest that you should feel obligated to answer everyone's questions. Thanks for all you do!!!!@@shawnwillsey
Take care when you, “screech to a halt”. 😊 I am a newcomer to geology but feel as though I’ve been interested all of my life without labelling the interest. I’ve so much to learn. The stews of various crystals sound like mixtures of musical notes making novel music or poetry.
Thx for the end-stage crystallization explanation, that solves old wonders-
Oooh I’m saving this one for future reference. The Inyo mountains in Owen’s Valley, CA have some cool pegmatitic granite where I’ve found amazonite and beryl crystals. I have not yet run across tourmaline. Thank you! 😄
Thanks Shawn, fantastic geology in one road cut. Jim from Dartford UK
Great location. I've never seen crystals so big in nature. Thanks!
That's interesting. I used to live in Cornwall, and of course I was well familiar with the granite, which typically had large well formed orthoclase, and must have been forced up from the batholith into cooler areas as a sort of hot crystalline mush. What you were looking at was evidently the last bit of partly liquid material being forced up from deep down
I’ve heard of tourmaline. Some rock hound jewelers use it to make jewelry (necklaces, earrings, etc.). Cool to see the rough material.
Tourmaline is one of my favorites!! Watermelon variety
So happy to see you in my back yard
Awesome! Thank you again! How beautiful! I would LOVE to have some of those rocks and minerals for my collection! Lucky you!
Thank you, I love these roadcut videos!
Glad you like them! Thanks for your support .
Really enjoy the road cut videos! So far, this one in particular -I would probably stay forever, picking bits and pieces..😅
Wow, I wish I had known about this before I went to the Black Hills. I found the Black Hills interesting for the rocks I saw there. I was very much interested in the Native American history there. I knew at that time it was not my personal history. My people were from the NY coast. But during my degree , I learned the history of the Black Hills and other Plains regions. When I got to South Dakota, I was amazed by the geology there. This pegmatite is amazing.
Brilliant road cut lovely minerals thank you 🙏
Thx Prof for another fascinating vid. ✌🏻
You had me at large sparkling crystals ❤
Great video Willsey! Cool seeing the intrusion and the minerals. That feldspar deserved more time!😃 Interesting to learn how those certain minerals precipitate out and are to be found in that water rich magma. Water is crazy. That it's known that these processes lead to these minerals and here these minerals are. Very cool! 🙌🏾👍🏽🙏🏽
We climbed the Royal Robbins climb, Tricouni Nail / Cerberus, a distinctive three-headed spire in the middle of the Ten Pins cluster near where you took this footage I think? Anyway, I recall climbing on large crystals all the way up. You get a sense of how old the rock is on that climb. Another great and educational video.
Pegmatites by David London is my favorite book ive ever read.
Thank you, that was so interesting.
Good information! Thank You!
That's a really interesting cut, Shawn. Well spotted! Thank-you. It would also be interesting to check the opacity of some of those crystals. When seeing interesting road cuts, I often wonder whether any of the people who made them had any geological interest in what they were revealing. More likely, they were paid for results, and didn't have the time to stop and investigate.
Very interesting Pegmatite. I would have stopped too. I'm pretty sure the Tourmalines are the Schorl variety. Thanks for sharing!!
Thanks for you knowledge sharing.What would be interesting to me the time frame formation of crystals of the size your viewing and the depth and temperatures of there formation.
Thank you professor 🤔
Did my field camp in the Black Hills from Illinois St in '78. We visited the Ada Mine (if memory serves) and other pegmatite outcrops. I collected some huge tourmalines with nice terminations, kyanite, spodumene, and the ubiquitous mica books and other odds and ends. Great memories
Wind cave was such an awesome sight!
Field camp 1980 there was a mine near there we went and the crystals were at least a full foot long . The hills are awesome
Spectacular!
I was lucky enough to go on a mine tour of Bernic lake Manitoba . Tantalum was the element they mined from tantalite. But there are giant spodumene crystals as well, beryl, tourmaline, lepidolite fabulous stuff.
Cool.
The most interesting rock unit I've encountered up here in northern California on the Feather River is this giant pegmatite I discovered... It begins at the level of the river and goes up 400 or 500 ft in altitude, and spans several tens of acres at least. Some green tourmaline, "graphic granite" looking stuff, lots of I assume feldspar, that is a delightful peach color... some slightly rosy quartz crystals... an encyclopedia of mica...
A big section of one side of it appears to be tailings cuz they've blasted out a bunch of it putting in giant power lines and tunnels for the train and hydropower plants and stuff... My yard is littered with rocks from that zone.
Peace, man.
Way cool spot to stop at in the Black Hills. Never know what you can find if you get close enough to the ground in a road
cut which is just east of Pringle, SD.
One of the first things I did when I started working for the Black Hills National Forest was review a permit application for a pegmatite mine. I remember thinking wtf is pegmatite? Now I know. Thank you Prof Willsey.
Nice, very nice
It would have been interesting to have been there as the road workers were cutting through that terrain. One could have collected fresh samples of the minerals.
REQUEST. Would love to hear more about the geology in Southern CA. Specifically Anzo Borrego desert and the large boulders in East San Diego County around where I live in Poway.
I lived in the Black Hills for a portion of my childhood, I wish I could go back, except for the winter cold...screw that.
I want a little piece!😊
Nice find Shawn! The Black Hills and the adjacent badlands are a great place to geologize (is that a word?). There's so much going on in that area. Will you do a video on Devil's Tower? Or on the gold mines in that area? Isn't there some kind of crystal cave too? Sounds like you're having a fabulous road-trip before winter sets in. Keep the great videos coming, they are much appreciated.
Geologize and geologizing are very much words in my vernacular. Devils Tower videos coming on Sunday.
HAH! Love it! You've coined an awesome word and I'm stealing it every time I take a trip now to 'geologize.'
Thank you! What are the bright yellow things? It almost looks like a crust on the specimen with the tourmaline, but then there were bigger yellow crystals in the hillside too.
Awesome find Professor! Regarding the schist that is intruded by the pegmatitic granite, are schists always indicative of an ancient subduction zone, or is that more specific to blue schists? What does this particular schist tell us?
Pegmatites such chaotic jumbling makes it clear that these formed relatively rapidly (geologically speaking) as in faster crystal growth than would be expected under slow crystal formation conditions.
I wonder what would happen if a pegmatite breached the surface? I would guess its something like a particularly mineral rich hydrothermal system probably with an explosive phreatic component as it first depressurizes.
Would the water rich pegmatite dike be an uplifted intrusive remnant of the "flat slab" model. Or is it related to the Siletzia/Challis magmas? Or something else. This dive into geologic history has really left my brain a bit scrambled in a focused sort of way.. Less need for fungal supplements.
I need to travel more.
And already the Black hills is living up to it's name😊
Where did the water come from in the magma?
Ich bin begeistert!
Beautiful rocks of billions of years ago
Thanks
Thank you!
Hello Shawn from Willspoint Texas
Grab me a rock !😂
Driving with a geologist always ends in roadside stops. It is in our blood.
That is some strange looking rock.
Sooo close to 70,000!! Come on folks, like, subscribe, and hit that bell!
Would you expect Spotemune and staurolite?
G-nice rocks
If you are into fossils at all you need to see the World Fossil Finder Museum in Hot Springs only a little way from the Mammoth Site.
Curious: you’re driving along and pull over to check out the layers. Do you know the age of the layers based on experience/sight, or based on knowledge of the area (black hills) or do you look it up ??
I usually have some references with me for exact ages. Sometimes I know enough of the region's geology through reading and studying.
That looks kinda a good area to prospect lol
Yes, this counts as Random Roadcut, too bad it is so far from Calif :-) What camera are you using, at first I thought it was a GoPro, but the shadow looks almost like an iPhone?? Thanks for doing these!!
Usually use GoPro but if I want to zoom in on details I use iPhone as I did here.
Thanks, Looking forward to the next vid!!
@@shawnwillsey
does mica always or usually present in pegmatite? thanks
Yes. Mica is common in pegmatite.
❤❤❤❤❤
QUESTION: WHERE DO YOU FIND BLACK HILLS GOLD? ie Source area? Shawn, I (DavtheRockSlayer) read through all the questions so far and I didn't see where anyone asked about where Black Hills Gold is commonly found. I always "screech to a halt" when I see pegmatites in roadcuts too (that is unless the wife is in the car as I know that would result in significant criticism and complaining from her). The crystals are almost always amazing in pegnatites and I thought hydrothermal vein deposits were a common place to gold. PS. I was also wondering if you forgot your rockhammer, lol!! glad to hear you didn't.
PSS. I'm proud to say I never "lost" my rock hammer; though I must admit having to backtrack numerous times to search for it!! LOL!!!
I can't resist my smart ass answer. There is lots of Blackhills Gold to be found in all the jewelry stores around Rushmore area. I bought some but wanted more.
Shawn, the black tourmaline is cool, but what causes "watermelon tourmaline "?
Quick answer: Some gem tourmalines (not black) can crystallize in zones, from the inside out, or lengthwise, alternating pinks, colorless, green, or blue. Brazil, California, Afghanistan and Madagascar are likely places for these color forms.
@@richarddavies7419 Thanks!
@2:42 - *"Uhh whud you call me?"*
Awesome rocks! Only thing I would ask is just edit out the parts when you're trying to find something or otherwise not useful content
Did you retrieve your rock hammer?? You put it down and filmed it, but I didn't see it in your hand as you walked back to your truck.
Got it.
I was thinking the exact same thing!!! Given that my handle is "DavtheRockSlayer", I would be lost without mine. Though, after being scolded by professors to go easy on the outcrops, I put my rock hammer away and got employment in industries using drill bits, core barrels, and hand augers!!! It is good that you mentioned having respect for outcrops and that "we" should use care when "perusing" an outcrop!
Could you be so kind to talk about the earthquakes going on near Phillipines, ???
A shallow (33 km), M7.6 quake struck the Philippines. The quake occurred along a subduction zone where the Philippine sea plate slides beneath the Eurasian plate. The quake was generated along a reverse fault (up/down motion) along this plate boundary. No significant tsunami was generated.
😂😂😂😂😂
Get your hammer!
Pseudo-hexagonal.
Rocks 🪨 are such an awesome product of our world. The variations and intercity show the beauty all around us.