PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
Great Rocks, Summer Excursions, and Confusing Minerals
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After a long break from recording, Chris and Jesse return to our studios to discuss our extremely busy summer. Jesse recaps his trip to Hawaii where he saw some amazing geology. He also talks about teaching field camp in Idaho to some of the Penn State undergrads. His favorite though, was continuing his field research in the Northwest Territories of Canada. He and his PhD student collected over 1,000 pounds of rocks. When asked about his favorite rocks seen this summer, Jesse didn't hesitate - the ancient rocks in Northern Canada. The toothpaste rocks won out over the much younger pahoehoe rocks of Hawaii.
Chris talked about taking 26 high school seniors out West for 3 weeks on the field course that he teaches. They went to the South Dakota Badlands, Black Hills, Devils Tower, Grand Tetons, Yellowstone, and Glacier National Park. The floods that ravaged Yellowstone in early June didn't prevent the students from learning about the incredible geology of Yellowstone. Following this, Chris returned to the West with his family to hike and climb. They went to the flatirons of Red Rocks and then on to Long's Peak. The Long's Peak granite was easily his favorite rock of the summer. The rock is interesting because it is a porphyritic granite. The huge phenocrysts are peculiar because they are not randomly oriented. Instead, they are aligned in a preferred direction which is a topic of current research. After leaving Colorado, Chris and family spent the next two weeks banging around in the Tetons.
We wrap up the episode by discussing a couple of mineral pairs that can be confusing to identify in the field. Join us as we have a casual conversation about some incredible geology!
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Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. Oh, well, I can see I've got fun, Chris, today. Happy Chris. You always have fun, Chris. Always have them. How you doing, Jesse Rymank? Oh, Christopher Boy. We're back at it after a long time. It's been a minute.
SPEAKER_01This I think is our longest break, isn't it? I haven't seen you in a long time. And you know, you uh I missed you too. You haven't improved though.
SPEAKER_00No.
SPEAKER_01I'm looking at you right now.
SPEAKER_00This summer has done me dirty here a little bit. It's has not improved me.
SPEAKER_01The field took its toll.
SPEAKER_00I got COVID, the whole thing, you know, it just took its toll.
SPEAKER_01But you know, it's all good. Hey, because it's been a while, Jesse. Let's do some intros.
SPEAKER_00Let's do it. You are Chris Bohuis, my former high school teacher, high school earth science teacher extraordinaire from the great state of Michigan. You taught me uh ninth grade earth science, uh geology, basically advanced placement geology, um, another class that I really didn't do much in, I think, and field course. Oh, come on. Now that's not true. That is not true. Well, my independent study, you know, I did a few things.
SPEAKER_01That hurt just a little bit right there. Yeah. Yeah. Okay. Well, I was gonna say a lot of good things about you, but you're Dr. Jesse Rymanck. You went to Hope College, got your bachelor's in geology, and then you went to the University of Alberta in Canada and got your PhD in geoscience. And now you, I don't know, somehow you landed a great job at one of the premier geology schools in the country, Penn State University. So that's awesome. I I do have to say, first of all, yeah, you learned a lot in geology, but you're right, you didn't do much because you you were more like a bump on a log than anything else. I mean, I I seriously had to check your pulse to make sure you were still with me. I did that a lot. I think.
SPEAKER_00Yeah, I I do remember that. Yeah, there's a lot of pulse checking.
SPEAKER_01You had no personality back then.
SPEAKER_00I don't know what happened, but now I'm not shy anymore. Um that's true. That's true. So like we alluded to, it's been a while since we've sat down and recorded, and we've both had pretty, dare I say, adventurous summers out there in the field.
SPEAKER_01Yeah, but hold on, before we jump into that though, you had something else you wanted to talk about. Oh, yeah, that's right. Good. Yeah, yeah.
SPEAKER_00We updated our website. So before we get into what we're talking about today, we updated our website. We also added in a donation support us link. And uh so you can go there. You can check out our website, planetgeocast.com, and uh you can support us. We're not making any money on Planet Geo, and we're just uh burning money, and so help us not burn as much money doing this, I guess, would be the exercise. You know, donate or don't, it doesn't really matter to us, but uh we like the support. We've had a couple already and we really, really appreciate it. So uh planetgeocast.com, it's a mostly updated website there, and stay tuned to that space. There'll be some more stuff coming at you in the next month, probably.
SPEAKER_01Um yeah, we do. Jesse and I, we've been working really hard on a new project that I think if you like this, I think you're gonna love that.
SPEAKER_00Yeah.
SPEAKER_01We're really excited about it. That should be coming out in the next month, right?
SPEAKER_00Yeah, totally. We're uh tidying up some things and it'll be a work in progress for a while, but it's coming at you in the next couple weeks or a month here. So stay tuned to the podcast stream. We'll talk about that more there. But back to today, Chris, we've been I don't know, uh adventuring out and about. We've been out and so hold on, Jesse. Let's give them a rundown about where we're gonna go today. Okay. Okay, good good point, Chris. So we got I'm just too excited. I'm gonna launch into stuff. I mean, you know, just ready to launch into it. Well, first of all, you teased me a little bit before we hit record here about a very funny story about yourself that I think we're gonna get to first. I'm really excited to hear this. But what we're really talking about is that you and I have been out in the field. We've been doing geology of different kinds. You've been teaching the field course, you've been out with your family, I've been up in the Arctic Canada doing field work, and so we're gonna kind of summarize that a little bit, talk about what we saw. And then we also had several people reach out via Facebook, emails, Instagram, and sort of ask about mineral identification or commonly confused minerals. So we didn't have a lot of time to put together a huge episode on just that, and this is a huge topic. So we're just gonna go kind of off the cuff, right, Chris? Like, what's on the top of our head when people say what are the commonly confused minerals? And we're just gonna briefly summarize a couple of them. Is that a fair summary?
SPEAKER_01You bet. We're gonna do a much more detailed thing on this. We need to really like do something with all right, how do you identify rocks in the field? And that's a hard thing, it's complicated. We're gonna tackle that coming up in the next, well, little while. Yeah, and it's a yeah.
SPEAKER_00I mean, it's a lifetime of learning how to identify rocks and minerals in the field, but we can give a bit of a guide. So we'll sort of lead into that a little bit. But Chris, I'm itching to hear what happened today.
SPEAKER_01So um today was the last day that we had. Uh you know, we're back to school now, so we're back in the grind. You and I are kind of easing our way back in the routine, right? We had some students in the building today just doing an orientation. It was the freshmen, you know, so they're young kids and so on. And we start on Monday with everybody's there, okay, and full on now. But so I'm walking around the corner. Okay, now I gotta set the stage because now everybody knows what I look like. I'm 50 years old, I have a goatee.
SPEAKER_00It's mostly it's mostly white and very bald, very, very, very bald. You know, very bald.
SPEAKER_01Uh yeah, I shave my head. Yep, that's that's right. Um, and so I walk around the corner, and a kid who's walking next to another teacher looks up at me, his eyes light up, and he says, Grandpa Gort.
SPEAKER_00Oh my god. Oh, that is so good. Oh, a nickname has been established for eternity here. Grandpa Gort. I know.
SPEAKER_01Grandpa Gort. Yeah. I looked up, I'm like, excuse me? What? And he's like, oh, oh, and he recognized that I'm not his grandpa. Oh, this is gold dust. He said, You look just like my Grandpa Gort. Oh, this is like, oh no. It's made my week.
SPEAKER_00I was having a rough, stressful week, and this has made it, Chris. Oh, this is gold dust. I gotta write this down so I don't forget it. Grandpa Gort.
SPEAKER_01Grandpa Gort. Uh, you know, Jesse, look, what do you do in a situation like this? Right? I'm just gonna lean into it.
SPEAKER_00There's an Yeah, you gotta you know there's no way out. There's no gracious way.
SPEAKER_01There's no way out. I gotta embrace it.
SPEAKER_00It's kind of like when you like, you know, trip on the hiking path. You just gotta kind of jog it out and pretend like you didn't trip, right? Like that's right. There's I and hey, I taught you that. I taught you that.
unknownOkay.
SPEAKER_01You don't know that I did. I taught you this. Well, come on now. Okay. When those rocks reach up and grab your ankles and you start tripping, you just jog it out like you meant it to happen.
SPEAKER_00That's the only way to do it.
SPEAKER_01So, yeah, that's that's my day. Grant foot court.
SPEAKER_00All right, well, we'll see if we can build your ego back up here, Chris, a little bit. Okay, but all right.
SPEAKER_01Well, hey, Jesse, let's get down to business. Um, let's start with you. Okay. What what kind of cool geolog? Where have you been? What kind of cool geology did you see this summer that our listeners might want to hear?
SPEAKER_00Yeah, well, I had a pretty good summer as far as travel goes. It was a fairly um, well, it took a lot of organizing. But I taught our undergrad field course, our Penn State field camp goes out. The course is six weeks total. Uh it goes drives from Pennsylvania all the way out to Idaho and then down to Utah. Um, and I spend a lot of time doing a variety of different stuff. But I flew out for a week in Idaho, right by the Craters of the Moon National Monument. We looked at a metamorphic core complex and mapped some faults and some interesting rocks there. So that was one week. I also had a conference in Hawaii, big bummer.
SPEAKER_01Oh my gosh. Yeah. Saw some basalts and some beaches.
SPEAKER_00Did you see red lava? I did not see red lava. I didn't have any time, unfortunately, to do any touristy stuff. I was at the conference, you know, I went to the beach a day uh and you know, did the beach thing, and then we did a tour, a driving kind of tour, driving, hiking a little bit, but we were on the Bega Island and in Honolulu basically, and then the conference was the rest of the week. And then I had to head back to Pennsylvania because I was organizing a field campaign into the Arctic of Canada, and I was up there for two weeks with a PhD student who just started and a couple of colleagues way up in the Arctic Circle collecting rocks from up near the Arctic coast. So that was really fun uh and tiring, and we got back a couple days ago. So I'm recovering from that a little bit still. So that was my summer, really.
SPEAKER_01So did you collect some big old rocks from uh Northwest Territories?
SPEAKER_00Oh man, we took back well, they're in shipping right now, but probably a thousand pounds of samples, and some of them are Oh, did you really?
SPEAKER_01Holy crap.
SPEAKER_00Yeah, there's like you know, 25 five-gallon pails of of rocks.
SPEAKER_01Um, this is gonna be uh What's that cost to ship back?
SPEAKER_00Well, a very small amount compared to the total cost of the field work. So we had a float plane that was flying us around collecting samples. This was in this, um we've talked about it before, but looking for ancient diamonds in ancient sediments. So this is that project. So we're kind of flying around sampling a bunch of different sediments, ancient sediments, and we're gonna look for diamonds in them and also prospecting for really old rocks.
SPEAKER_01Cool. So I have to ask this question then. You've been a lot of different places, seeing a lot of different rocks then. What's the favorite rock that you've seen this uh this summer?
SPEAKER_00Well, this was Yeah, there's no question this was the best one. We basically one day we flew in this little tiny float plane, it's like a five-seater pilot plus four people, and we couldn't find any rocks. We had four people, but three of us flew up to the Arctic coast. So we landed on the Arctic Ocean in this little bay, and the outcrops there are ancient gneiss exposures, G-N-E-I-S-S, the rocks I study, and right on the coast, there's no lichen because the sea ice scours it all away, and the sea spray doesn't allow lichen to lichen is that biology that likes to cover up our geology for everyone that doesn't know that. Oh, and in northern Canada, lichen is everywhere and it gets in the way of everything. And these really beautiful rocks are covered in lichen, you can't see shit. So on this coast, we landed. I'll send you a picture of this, and maybe we'll share one on the social media feed here. But these rocks, this was toothpaste rock. I mean, this stuff was spectacular. Like different fold patterns, it was just toothpaste. I mean, this is highly metamorphosed gneisses that are folded, bent, faulted, and we're just walking like kilometers along this Arctic coast. We had a stunningly beautiful day up there. It was like 75, it was flat, calm water. We collected samples all day, then we took a dip in the Arctic Ocean. I mean, it was just this it was geology porn. I mean, I described it to our float plane pilot. He was like, Oh, what kind of rocks are you collecting here? I was like, Well, to be honest, the last two hours we've just been wandering around taking photos. This is geology porn. And he looked at me kind of quizzically, he's this like 65-year-old guy looked at me quizzically, and I was like, you know, the the rocks that get all the geologists kind of worked up. And he got a good chuckle out of that.
SPEAKER_01So he'd never heard that before.
SPEAKER_00He'd never heard the term, no, yeah. He's been around geologists a lot before, but uh anyway, yeah. So that was um spectacular.
SPEAKER_01All right, so I have a question then. Am I gonna get one of these rocks? I don't require a big piece, but I I feel like I deserve a piece.
SPEAKER_00Yeah, I think you I think you might. Yeah, we'll have to we'll work something out on the side here. Yeah, we can do that.
SPEAKER_01Well, okay, but I don't need your leverite already. Yeah, no, no, no, no.
SPEAKER_00I don't need to like I need to look at I need a good piece. I don't collect leverite anymore, man. This is serious stuff. But yeah, I mean we've got some amazing there's some I the problem is is the scale, like the hand sample, when you have a spectacular rock, a hand sample doesn't really do it justice. Like you need a countertop slab cut out of the outcrop, right? It was really hard to find even a big sample, like one that you could carry, that really showed the beauty and the complexity of these rocks, it just doesn't do it justice, really.
SPEAKER_01Yeah, you know, you and I we've evolved in our collecting habits. We are into massive rocks. I mean, the bigger the better. That's that's kind of where we're at right now. So I get it. Yep.
SPEAKER_00These rocks were just stunning, and it really was when rock is heated up to high temperature and at high pressure, it's toothpaste and it can be squished and bent and folded and deformed, and it just flows like toothpaste. These rock crops really showed that really well.
SPEAKER_01That's great. I want everybody to understand how big of a deal it is for him to say this because I've gotta assume that you saw some pretty spectacular Pohoihoy lava flow texture in Hawaii.
SPEAKER_00Yeah, we did see some. There was some pretty cool stuff. We didn't go to any of like the really recent eruptions, but we did walk through the cliffs where you can kind of go through and you can see a cross-section through the Pohohoi features. Describe what Pohoihoi looks like a second. Yeah, Pohoi is this flow pattern. It looks like ropey texture on top of a basalt when the lava flow erupts and the top of it that kind of skim cools, so the very surface of it is cool and solidified, but just underneath the surface, it's still liquid or it's still lava. Then it kind of rolls the top pattern, and you get this really ropey texture to it. It's just beautiful stuff.
SPEAKER_01Yeah, it's it's so cool. It's spelled P-A-H-O-E-H-O-E, and it's pronounced Pohohoi, and it's a flow texture. It's black, smooth, ropey, kind of this twisted, braided appearance. It's really spectacular rock. And so for you to say this other one, like that, that means that that's that's pretty pretty awesome stuff.
SPEAKER_00We actually saw Pohohoi in the Craters of the Moon National Monument, where we went there for a day during the field camp, and that's where you taught me a lot of stuff. I know we were driving along the Snake River Plain, and I was having flashbacks to in high school. We've talked about this before, I think. When I was sitting, I think I sat in the front of the bus, and this was the moment I really decided understanding the earth was like really just what I should do. This is a really cool thing. Because I remember we were driving from Yellowstone to Craters of the Moon Nashimana, through the Snake River Plain, this huge, just open plain. And you were driving a big yellow bus, you're driving, students are all in the back, two to a seat, basically. I wandered up to the front and I sat on the steps, you know, the front steps, the rubber steps of the bus, and I was just asking you questions, and then you you kind of push me a bit, and you're like, hey, what are we driving through right now? This is Big Valley, we just left this big volcano. What are we driving through now? And it took me forever to figure it out, and I couldn't figure it out. But anyway, I was having flashbacks about this, about as we were going to Craters of the Moon, but we saw amazing Bohoy there too, like we saw, you know, in 2000 whatever. I won't mention it, but 200 whenever when I was in high school.
SPEAKER_01You know, that brings up a point. You know, we've done Yellowstone. We talked about the Geology Yellowstone, but we haven't done the end of the story really of Yellowstone, which is really craters of the moon. It's an amazing story. That park is so underrated that I think that we probably need to do some justice to it and do an episode of it.
SPEAKER_00I would agree. I would agree, which leads nicely, Chris, into what have you been up to this summer? I mean, you've been there, presumably this summer.
SPEAKER_01This has been, I think, the busiest summer that I've had. I right after school let out officially, Jenny got certified in Woofer Wilderness First Responder training. And then we were home for I think four days, but that was just enough time to like regroup and equip and get everything set up for the field course that I teach out west. So took 26 high school seniors, some of our best out west, and um it was, you know, we went to the places, we talked a lot about them, and and we were pretty much right on with the releases that we had. We released Devil's Tower, we released the Badlands while we were there.
SPEAKER_00Let me interrupt. If you haven't listened to those episodes, go back a few episodes several weeks ago, a couple months ago, and you can listen to those and sort of follow along the field camp that Chris leads and uh learn about the geology of those areas. Anyway, go sorry, keep going.
SPEAKER_01Yeah, that's right. So, yeah, Badlands, Black Hills, then Devil's Tower, and then from there we we head straight to the Tetons and the Tetons this year. The Tetons never disappoint. I'm in love with them. Uh, there's more to come on that in a little bit. But then we went to Yellowstone, and this was interesting because Yellowstone recently had these massive, that it was a 500-year event at least, this flood event that wiped out the northern part of the park and the road system and the infrastructure there. Um you know, there's lots of sad stories that go along with that, but you know, we were able to do everything that we really wanted to do from there, went to Glacier, and Glacier National Park is amazing. We did an episode on that a long time ago now.
SPEAKER_00Yeah.
SPEAKER_01Um, but Glacier is just uh holy cow. It's an amazing place, and we spent uh actually all of our time in a place in the southern part of the park called Two Medicine. It's probably the least busy part of Glacier National Park, and uh two medicine is good medicine. I love it, it's absolutely amazing. In fact, one of my former students, she's the captain of the boat on two medicine lake, and so she takes tours every day, you know, and she runs a crew of like five people. Um, so she took us out, not the group, but she took my wife and you know, Andrew, our our friend, and my teaching partner and his wife took us out in the lake at in the evening and threw a couple lines in the water, caught a couple lake trout. Yeah, yeah, really cool.
SPEAKER_00That's awesome. This is all on the the field course, right? Yeah. And then where did you guys go on your family trip? You guys did a family trip after that, is that right?
SPEAKER_01Yeah, we're home for three days, and then we went to Colorado, actually. We went to Denver area and uh we caught a concert at Red Rocks, saw David Gray, it was amazing, and then we got up really early the next day after the concert, and we hiked up to the boulder field, um, which is about twelve thousand nine hundred feet up, and we made camp. And then this is inside Rocky Mount National Park, and then we uh we climbed Long's Peak the next next morning, got up at the crack of dawn and climbed that. You and I have done that. Yeah, beat the rush, beat the rush that's great. Oh, yeah, it was awesome. That's great.
SPEAKER_00I I do remember we had a very rainy, dreary day, but we managed to have our whiskey at the top. That was that was totally good. That was awesome.
SPEAKER_01We did, yeah. I didn't have any of that with us because we took my so my daughter on this trip got engaged, and so that happened in the Tetons, but I knew it was gonna happen. So my soon-to-be bonus son was with us on his trip like that.
SPEAKER_00That's a good one.
SPEAKER_01Yeah, uh, yeah, yeah. So uh he is not used to this kind of exposure. You remember Long's Peak has a it's not a hike, you know, that it's got a fair amount of exposure on that, and it was really interesting watching him move about that.
SPEAKER_00It's uh that can be a bit intimidating, that hike for sure. You gotta not look you there's some parts where you don't look down too much.
SPEAKER_01That's right. So the answer to to the question about favorite rock is actually on this hike. I'll come back to that in a little bit. Then we went to the Tetons and we spent about two weeks in Tetons. My bonus son um he proposed we hiked up to the base of the Middle Teton and made camp. And then at sunset is when he proposed to her. And then the next morning we got up at the crack of dawn and climbed the middle Teton. And yeah, it was awesome. So um, yeah, we spent like uh the you know, you talk about like this toothpaste kind of texture in these metamorphosed rocks. I saw a lot of that in the Tetons. I took a lot of pictures of it, I'll share those with you later on. Just absolutely like the you look at these rocks, all you can think about is how you want one in your yard. Yes, you know, I want to stare at that every single day. They're so unbelievable. They really are.
SPEAKER_00Um, and you know, there just there was a lot of that. That's a cool place, yeah. That's uh great, great summer. So the rock, let's let's talk about the rock. You said it was the Long's Peak one. Yeah, let's talk about this. The best, yeah.
SPEAKER_01The it was on Long's Peak, and and I think you have to remember this. It is this porphyritic granite.
SPEAKER_00So let me interrupt there. A porphyritic granite. Granite is a rock type, it's the light-colored, intrusive rock, so it's a magma that cooled underneath the surface. The grains are fairly large, you can see them with your naked eye, but porphyritic means it has two different grain sizes. It has really big grains and moderately big grains. And so porphyritic is a term that just says this granite has two different crystal sizes in it, some really big ones, and then the background will be visible pieces of usually quartz and feldspar and biotite, things like that.
SPEAKER_01Yeah, well said, my young sage. That was well done. Thank you. Um continue. You may continue now. But here's the thing, right? And this is what I want to talk to you about, actually, is that in a classic way, a porphyritic rock is thought to form, you said two distinct grain sizes, right? Big grains and then smaller grains within the same rock. Well, rate of cooling is almost always the factor that determines grain size in the rock. So if it cools slowly, the minerals have time and they get larger, right? So what you would have with this is it's thought to be that you have this slow, slow cooling, the crystals get big, and then this magma moves closer to the surface where it cools faster, and then the grains get smaller. But the thing is about this is that the big crystals in this, these feldspar crystals, uh, they're not randomly oriented like an igneous rock should be. These have a definite pattern to them, they are all lined up in the same direction. And that's what it makes it so cool. But what are your thoughts on that?
SPEAKER_00Well, I have some thoughts. They're not the most uh informed, but this is a hot topic in the science of understanding granites right now, like really hot topic. Traditionally, I think would say the textbook model would say that those big grains were in a magma, they cooled in a magma, they were growing in a magma, and then the magma started to flow a little bit, you know, it kind of moves from one side of the magma chamber to the other, and that would orient all the grains. And so you can see this. I've even seen this in Washington, D.C. Like a lot of the monuments, like the World War II memorial in Washington, D.C. on the National Mall, is made of a porphyritic granite, like the rock is a porphyry granite. You can see those big feldspar grains are aligned in a certain direction, they're all kind of pointing in one direction. It's really beautiful. The idea would be the traditional idea would be that the magma's kind of oozing, it's sort of slowly flowing a little bit, and then the grains get aligned by that flow. There's an alternative interpretation that suggests that that's all what we call subsolidous or solid state chemical movement. So sort of fluids flowing through the rock that could crystallize those things. That's a little bit of an oversimplification of the model, but that that's happening after the rock has solidified, and then those grains are growing much later, and at lower temperature, not magmatic temperatures, but still high temperatures, you know, 400-500 degrees centigrade, but not magmatic temperatures. And so there's a debate in the literature about that. And actually, this is a huge rabbit trail to go down, but we should probably try and find somebody to interview about this because it's a fascinating problem in geology.
SPEAKER_01It looks to me, I mean, when you look at this rock, it looks like it was flowing as it solidified. So, what you said, like theory number one, that's the way it looks. That makes the most sense to me.
SPEAKER_00Totally. Totally.
SPEAKER_01Um, and these crystals are huge, some of them are over an inch long.
SPEAKER_00Yeah, I mean, they're bigger than your thumb.
SPEAKER_01Oh, yeah, they're they're so and they're pink and they're white and various shades in between. Some of them are orange, bright orange. So they're beautiful. And because it's not particularly common, that was my favorite rock that I saw this summer was easily the longspeak granite for sure.
SPEAKER_00Those rocks are so spectacular to see in person. And you know, you get the feldspars and they kind of glint the cleavage direction, sometimes glints at you if you're walking past, so it looks like it's cliffsides kind of like glinting and shining at you, like little diamonds kind of sparkling out. You go up close and it's a big feldspar that you know, when it hits a certain crystal face, it flashes at you. It's beautiful.
SPEAKER_01And it's all over, too. I mean, you're stepping over all this rock. So you know when you're walking, your eyes are down, so you don't trip, you know, because it's really a rocky, rough trail. And you so this rock is just literally that's all you see all day long. It's really cool. So, yeah.
SPEAKER_00That's a that's an excellent one, Chris. Hell of a summer. So let's sort of wrap this up by talking about a few minerals, commonly confused minerals, that we could give a few tidbits about how to distinguish minerals that look alike. And we've had, again, just to reiterate, we've had several requests from listeners in this sort of general space of how you know we like collecting minerals, we like collecting rocks, we're out there. Help us identify these things because it can be massively confusing. And I can attest to that. Anybody who has gone out looking at rocks can attest to how difficult it can be to identify specific minerals. So we're gonna break down two different pairs of things that are commonly confused. This is just off the cuff. We haven't really put a lot of thought into this, just you have a vast experience with what people get wrong in the field, right? You're the expert on here on like what confuses people, what throws people off. So what do you think? What do you what should we start with?
SPEAKER_01First of all, I want to say that like if you're interested in this kind of thing really, and and some of our listeners clearly are because of the questions that we're getting, then you need to just go uh get online and buy yourself a hand lens. This little magnifying uh geology little hand lens, it folds in on itself to protect itself. You put a little uh like a shoestring around it and and you wear it at like a necklace.
SPEAKER_00It'll cost you 10, 15 bucks. You can buy 40 ones, but 10, 15 bucks will get you where you want to go on this.
SPEAKER_01That's right. They're they're not expensive at all, but they're so helpful in doing this kind of field identification of minerals and allowing you to see not only just identifying the minerals, actually, but I also identifying rocks, classifying rocks as whether it's igneous, metamorphic, or sedimentary. So that'd be my first thing. But the two minerals that I think are confused the most often are it's a mineral called hornblende, it's a type of amphibole, which is black, and then a mineral that is called shorel, which is a type of termaline.
SPEAKER_00Ooh, these are these are tough ones. Uh yes, these are absolutely tough ones, Chris. Good pair.
SPEAKER_01Yeah, because they commonly occur in granite. Okay, if you look at a granite, granite is mostly light colored. It's gonna be loaded with like shades of gray, that's usually the quartz. It's gonna have white, which is usually the feldspar. It'll have often pink or orange or this kind of lightly shaded mineral that's another kind of feldspar that's in the rock. That's what most of the rock is, this light-colored stuff. And then it has these like black, dark colored minerals that are kind of peppered throughout it, right? Usually those minerals are gonna be biotite, which is super easy to identify because it's this like flaky mica kind of mineral, okay? Or it'll be horn blend, this black amphibole, or it'll be shorel, this black tomaline. Those are like the three, would you agree with me? Am I like I don't want to oversimplify?
SPEAKER_00I know you're gonna object to me because you're like, well, Chris, uh No, this will be the rare occasion where I do not uh disagree with you. Absolutely, those are very commonly confused ones and difficult to tell apart. I mean, really quite difficult to tell apart. You and I have seen a lot of both of these in both just rocks that we've seen together uh out there in the field, and also in mineral collecting locations. Like amphibole is very common. It is one of the 10 rock-forming minerals. It's uh has a lot of iron, magnesium, so it's black. It has silica, oxygen, it has its hydrous, so it has a little water in its crystal structure, but it's a garbage bag mineral. Like it has all sorts of different elements in it. And shorel, this black tourmaline, is really very similar. It has the most complicated chemical composition of maybe any of the minerals that any undergrads are asked to memorize the chemical formula for.
SPEAKER_01Two things pop to mind. One is like just a visual thing, right? And then the other thing that pops to mind is some sort of physical test that you could do to it. Okay. The visual thing is that shorel, this tourmaline.
SPEAKER_00So can I let me interrupt there, Chris? And it's S C H O R L is the term for the black tourmaline. Many people will be familiar with the fancy watermelon tourmaline that people will see in the museums, but this is the black version, choral.
SPEAKER_01Yeah. Uh the visually, it often has very prominent vertical striations on the crystal faces. And that's the thing that you can like with your hand lens, especially, you pull that thing out, and you man, you just feel warm and fuzzy when you're like, oh, I get to use my hand lens now, and you pull that thing out, you know, and you that's true. You look like a total nerd, but that's okay. But you see these vertical striations, and these striations are these vertical, they look like scratches on the crystal face of the mineral, but these scratches are perfectly parallel, they're clearly not a random thing.
SPEAKER_00This is the way the crystal grew that caused these striations, and they go all the way down the crystal, so they'll run all the way along the whole crystal, whatever the size of the crystal you're looking at, it'll run all the way down the whole length of that.
SPEAKER_01And we say run down it because shorel is this kind of long, skinny, pencil-shaped crystal. And so they run parallel to the length of the crystal. So that's the easiest way to see it. The other thing is if you're able to do any kind of physical test on it at all, shorel is extremely hard. It's harder than quartz. Um, and quartz is extremely hard. So horn blend is quite a bit softer and won't scratch glass. Shorel, get it anywhere near a glass plate and it'll scratch it. So I think to me, anyway, those are the ways to quickly spot the difference in the future.
SPEAKER_00So I there's another one here, Chris, that I tend to rely on quite a bit on this amphibole versus shorel, and it's kind of the mineral associations, like what else is in the rock? Because amphibole is a very common igneous mineral, meaning it forms in granites. You mentioned granites, it forms in more mafic rocks like gabbros as well. But it'll almost always have biotite in the same rock, in a lot of biotite. So the the rock that contains amphibole will kind of be salt and pepper or even darker than that, like the background color. Shorel, we just saw shorel um the last day we were in the field. We went to some lithium-bearing pegmatites that are 2.6 billion-year-old lithium-bearing pegmatites that some exploration companies are exploring for as a lithium deposit, and there's shorel in them, but they don't have biotite in them as well. They have huge K-feldspar crystals. They have huge quartz crystals. And Chris, you and I have seen this in both Maine and in the Black Hills of South Dakota. The huge shorels almost always occur with quartz, feldspar, maybe some big books of muscovite, the the light-colored mica, but those pegmatites, those really fluid-rich things that form tourmaline.
SPEAKER_01That's right. And that's the thing you gotta emphasize here is that Doral, this tourmaline, is often associated with pegmatites, which again, this we did an episode on this a long time ago. You can go back and look it up, but it's this extremely coarse-grained texture in an igneous rock. So that's another thing, too. That's a really good point. That if you're dealing with a pegmatite, horn blend is not it's not excluded, but it's if you're gonna wage a bet, I would bet it's gonna be tourmaline or shorel in that.
SPEAKER_00That's a great way to phrase it, Chris. And that's a a really powerful tool for identifying minerals is what else is around it. And you gotta know your rocks, and you know, it takes some expertise to build this up. But you if you look at a rock, you're like, I don't know, is this shorel or tourmaline? Look at the other minerals in the rock. And if you can identify the other minerals in a rock, you'll be able to really make a very educated guess about is that shorel or is that amphibole?
SPEAKER_01Yeah, well, and and that's right. I think too, it brings up another really important like principle in geology is Bowen's reaction series, which deals with mineral assemblages. Minerals tend to only exist with other certain minerals, and so go back to the episode on Bowen's reaction series to get a refresher on that and that kind of explanation on why that's the case, because there's a definite reason why certain minerals don't exist together in the same rock.
SPEAKER_00Yeah, absolutely. That's a good set of minerals that are very easy to confuse with one another.
SPEAKER_01Did you have another one or are we gonna wrap this up?
SPEAKER_00Yeah, let's do another one real quick, just really briefly. I th there's two minerals that are really easily confused because they're the same sort of mineral group, is that's potassium feldspar and calcium-sodium feldspar called plagioclase. So plagioclase and potassium feldspar, which you alluded to, the big phenocris or the big large grains of potassium feldspar in the longspeak granite, that's easy to confuse with plagioclase. And there's no one trick to identifying these things or to distinguishing them. Plagioclase generally tends to be white to gray to dark gray to like really dark gray on a broken surface. And potassium feldsbar tends to be white to pink, like really pink. And so when they're both white, it can be really kind of confusing to distinguish these things. The only really good trick that I have is look at a weathered surface because plagioclase, no matter if it's the really dark, dark, dark gray version, or if it's the sort of lighter gray version, it always weathers to a really chalky white, like brilliant chalky white on the surface. Potassium feldspar or K-Feldspar doesn't weather that way. It usually weathers to a little bit more like the color that you break it. So if you have a rock that you have a broken surface and a weathered surface, you can usually really easily tell if it's plagiaris or potassium feldspar, or if it's both. Many of them will be both, but that plagiuclase always weathers to that really chalky white color.
SPEAKER_01I'm gonna take that and file it away because that is not the answer I would have given. Oh, what would you have given?
SPEAKER_00That's interesting.
SPEAKER_01So for beginning geology students, it's good enough just to recognize it and say, oh, that's a feldspar. But for my geology students, the class you took with me, the upper level class, that's not good enough. You have to distinguish between plagioclase and potassium feldspar. Uh and so I tell them to look at a cleavage surface of the mineral. Okay, so you have to have a cleavage surface under it, and you roll this around under the light. And when light hits that cleave surface, it flashes off, right? And what you're looking for are these striations on the cleaved surface. And when you see striations on that, that's plagioclase. Potassium feldspar doesn't have that.
SPEAKER_00So that's that's what I tell my students to do. That's a really good one, Chris. And the other one that you can use along those same lines is the opposite. When you see potassium feldspar, it's divided in half. The cleavage surfaces are divided in half. It's called what's called L bite twinning. So those big phenocris, the big crystals in the long speak granite, they were divided in half in the cleavage surface, meaning one half would flash at you, the other half would not. If it's divided mostly down the middle, that is diagnostic of potassium feldspar. And that is a for sure a foot potassium feldspar. It's a twinning that only occurs. Whereas the the striation twinning that you see in plagiuclase really only occurs in plagiuclase. So that's a that's a really good one. That's actually more diagnostic because you don't need the weathered surface to distinguish the two of them. So that's a good one, Chris. Excellent, excellent one. Yeah. Good stuff. Hey, well, that's I guess that's a wrap, but that's just a brief lead-in to mineral identification, rock classification. Like this is a huge thing, and we'll keep banging our heads against this over the next six to nine months because a lot of people are interested in it. So we'll keep having more little tidbits like that, but I think that's enough to kind of get started as you're out there in the world walking around looking at rocks and you see some minerals. This will give you some things to look for and uh some little keys to take note of to help identify minerals.
SPEAKER_01You know, we hit a lot of geology today, too. So just kind of more like subtle things in geology, I think.
SPEAKER_00Yeah, and those are so they're important. Yeah, important stuff. So, Chris, that's a wrap. Uh, you can visit us on our new website, planetgeocast.com, all the social medias, Planet Geocast is where we're at. And uh stay tuned to this space. We've got some more episodes coming out weekly and some exciting stuff outside of the episode feed, but you'll get news updates within the episode feed. So stay tuned to that for our upcoming project as well. That's right. Cheers. Cheers.