PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
The Rocks You Need to Know
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Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it worked, and why it matters to you. Let's see how it goes. See how this episode goes. Let's see what this turns into. Okay, Chris. Well, first of all, I have to say, there's a way that Crisple Ice comes into the Zoom room. Do you know this? Do you do you know the look you give when you come into the room? Um, was I a grumpy? No, no, no. You're not you're you're rarely, if ever, grumpy when we are doing Planet Geo. I mean, you know, you know that. You you you're not happy. Sometimes you need to vent a little bit at the start of something, but Well, I do have some venting to do today. Oh, good. Well, we'll get to that. But let me first say you come in with it's your it's Chris Bullheis's rock hunting focused look. It's this.
SPEAKER_00It's because no, it's you know why I gotta I alright, I know what's going on now. I know exactly why I'm doing that. It's because I have my three-screen setup, and when I first come on, if you beat me to the punch and you're already on, you're looking for me, I come in and I'm looking around trying to get everything situated, and I just don't want you to talk to me at that point. I just leave me alone, let me get everything situated.
SPEAKER_01Tightly furrowed brow, pursed lips, intently focused. I mean, it is the it's the crisp bullheist, like focused on something, don't mess with it.
SPEAKER_00I am gonna have a little sip of bourbon right now. Cheers to you, Jesse. Cheers to you.
SPEAKER_01So, this is gonna be a fun episode. I want to hear the vent, but this is gonna be a fun episode. This is a free-flowing episode that we we've really not talked about. This is just kind of unstructured. So we figured, hey, let's have a glass of bourbon and let's uh let's talk about one of our favorite topics.
SPEAKER_00That's right.
SPEAKER_01What do you got to vent about today, Christopher Balhoey?
SPEAKER_00Oh my gosh. So on Sunday, it was beautiful weather.
SPEAKER_01Yeah, we've had some glorious weather here recently, too.
SPEAKER_00So nice. And so we got everything situated in the morning. I think you and I met. We had to we had some business to discuss and so on. And so then I loaded up our bikes, I pumped up all the tires, put the bike rack on, loaded up our bikes. We were gonna go for a long bike ride. We get there, it's like a half hour drive. We get there, and my tire is flat. So I had pumped it up before we left. So that's a problem.
SPEAKER_01Do you have tubes or tubeless tires? What's your uh no?
SPEAKER_00I have tubeless. I have tubeless, yes. Anyway, that's a problem. I can't fix it right there. I I just don't have what I need. I wasn't expecting this at all. In fact, we'd all gotten like we got our clip-in shoes on, we got our helmets strapped in. Last thing I'm doing is I'm ready to go. And I saddle up and I'm like, uh-oh. We got oh no, I got a flat tire. So it's you and Jenny. We end up yeah, just Jenny and I. And we we so we came home, and uh, so today was my day that I'm gonna fix this thing. So I get everything I need, you know. I have a tool that I had to go buy because I didn't have it yet, the the core remover tool, you know. Anyway, I could not get that tire to seat on the rim for the life of me. Oh my gosh. So it took me literally two and a half hours to change a tire on my bike.
SPEAKER_01That's yeah, it was so that was frustrating.
SPEAKER_00It was very frustrating.
SPEAKER_01Those things that should be two-minute tasks, but there's some new technology involved, and you know, you gotta figure it out like it's impossible, you know, it doesn't work that well. I I must say, I mean, I don't bike. You get you this is road biking that you guys are doing, right? You and Jenny? Yeah, it's a cross-country kind of well, at least you can get out on it, uh, you know, this coming weekend. You'll be ready to go. Jenny won't be pissed at you. Because I did I called you later in the day with a random, random half-baked idea, and I got Jenny on the phone. And Jenny, first thing she says is, Well, Jesse, we're gonna go biking, but Christopher just didn't have his Christopher's bike was we had a flat tire, so we couldn't go.
SPEAKER_00So Well, you know the bull heistes. We adjusted on the fly, and it was such a beautiful day that you called. What you got was the result of Jenny and I sitting on the back deck. We were sitting in our Adirondack chairs, and we had two gen tonics.
SPEAKER_01That was that was definitely a thought, you know. Um, going back to a conversation we've had on this podcast about how there's there's no real rails in place in the bullheist household. There's nobody keeping you two in check. As soon as I picked it within two seconds of me poking up the phone, I was like, okay, they've been added again. The bull heisers have been added again over there. Just too. Well, we have fun. We have fun.
SPEAKER_00It's a it's a it was it was good. It was we made the most of the day.
SPEAKER_01Hey, if you're listening to this, you're driving through Hudsonville, Michigan someday. Call up the bullheistes, just swing by because it's bound to be a good time. Don't swing by. Don't swing by. Um don't swing by. Nope. Okay, so Chris, today we decided, okay, this is a listener question. This comes from Jamie. Jamie asked, well, he kind of asked Chris about the 25 rocks that you've talked about on this podcast that you teach your students. And it sort of the question was like, could you list them? And we thought, well, yes, we can list them, but it's much more interesting to kind of talk about why. And I think Chris, we we, you know, we talked about scripting something out here or not, but we decided not to because this is pretty like in our wheelhouse. And I think it's going to be an interesting conversation because there's some differences in what you teach, what you require your students to know, what I have the ability to rec to require students to know. But then also, like, what do we think about the valuable rocks? Like, what are the what really, if you're a passionate, you know, if you're a trained geologist, that's one thing. But if you're like a passionate um amateur geologist, what are the rocks you really need to know? Well, I don't know, what do you what are your thoughts?
SPEAKER_00Yeah, I I absolutely agree. There are so many niche rocks that we could get into that you know, you just but it's well beyond the scope of so I try I try to just think about all right, what are the basics? What do I want really everybody to know in terms of like what rocks are out there and what common rocks are out there and what do they tell you?
SPEAKER_01Yeah, what do they tell us? That's it, that's exactly right.
SPEAKER_00It's not naming the rocks and saying, Oh, that's a sandstone. That's not what's important. What's important is knowing that that's a sandstone or a quartz sandstone, because then what does that mean? What was the depositional environment? What was the interpretation of that rock then?
SPEAKER_01But you got to get it right at the outset, right? You got to know, you kind of got to narrow this down and figure out how to kind of identify this. And so a couple points here before we get started. First, we've done an episode on how to identify rocks that gives kind of an overview of this. You can go back and listen to that, but that's kind of more like a strategic, you know, what kind of questions should you be asking yourself if you pick up an unfamiliar rock in the field. We'll touch on that briefly, but but really we're gonna talk more about the actual rocks. You should probably know or you should learn about. One quick plug is that if people ask us how they can kind of support the podcast quite a bit. There's two ways. One is Camp Geo. Go to our app, that's the first link in your show notes, and we have we talk about these rocks. We talk about all of well, almost all of these rocks. Actually, we do. We talk about all these rocks. We have chapters there, it's free content. We have the images, importantly, on the Camp Geo app. So you have free content, basically the intro to geology class that Chris, you teach and at the high school level and I teach at the college level. Same class, same content. We have that in audio discussion form with the images you need. So, first link in your show notes, you can go there. We also have the geology of Yellowstone, geology of Grand Canyon, and Earth's climate that you can purchase there right now. So that's one way to support us. You can also head over to our website, planetgeocast.com, and there's a support us link there. So those are just two ways to support us. And I wanted to touch on the stuff that we cover, and because the second follow-up point here, Chris, is that we're gonna have another episode, which is in the weeds, which is sort of the rocks you don't need to know, but you might come across, like like these accessory ones, right? Because there's thousands of different kinds of rocks. We're gonna focus on the ones you need to know right now or what we think you need to know, right? And we're gonna format this by I'm gonna kind of interview you. I'm gonna you you sent me a list of the the rocks that you require students to to know, but at the outset, Chris, I'm curious how this list has changed over the 55 years you've been teaching this class. Okay, all right. Um, but seriously, it hasn't has it, has it? Yeah, yeah, and if so, how?
SPEAKER_00That's a good question. It hasn't changed a ton, and I'll say that the changes that have taken place are a result of changes in things that pop up on my Grand Valley exam from Dr. Steve Maddox.
SPEAKER_01Oh, interesting. Okay, right. That's that's right. I've I've forgotten that point. Because and for people, just as a backstory here, students myself included, we got college credit, and a bunch of local colleges and and regional colleges will give college credit because at the end of Chris Bullheis's high school geology class, you take the Grand Valley State University exam and then you get credit for it. So that's what you're referring to. How has that changed over the 20 years you've been doing it?
SPEAKER_00The test changed with respect to major format in that when we first started doing this, it was all short answer, fill in the blank. It was what's the name, what's the texture, and what's the interpretation of each rock? What's the environment of formation? Now the test is all multiple choice, and that's just because it's gotten big, right? He has so many tests and he has to grade, it's just impossible for him to do this. So he can just run them, you know, he can scan them and it's good to go.
SPEAKER_01So people will get a rock sample in their hand and they'll and it'll be like, is this diorite? Is this gabbro? Is this sandstone? You know, which one? Pick which one it is.
SPEAKER_00What he'll often do is he'll ask about the name and then he'll ask about the interpretation of that rock, you know. So one sample and he'll ask anywhere from two to four questions about that sample. Okay, gotcha. In a multiple choice format, which I thought when we made that transition, that I'm like, oh, my students are gonna nail this. And I have found that they don't do any better on a multiple choice test versus the yeah, foot free response test.
SPEAKER_01I mean, that's interesting that it's changed because the rocks haven't like the the important rocks haven't changed.
SPEAKER_00Sometimes he adds things in and it'll stay there for a while. Like he'll he recently added meta conglomerate or like pudding stone to the list, um, which I found interesting and curious. Uh maybe it's just because it's fairly common in Michigan to have those rocks.
SPEAKER_01I mean that's yeah, let's talk about that when we when we get to that one, because that is one that certainly stood out on this list to me. Yeah. As you know, like I wonder about that. Oh, interesting. That's one I certainly don't require. So let's start out with the obvious ones, I guess, Chris. And let's start out with the igneous ones. It's our home turf. We've taken a little bit of heat from listeners for being interested in igneous and metamorphic rocks above all else, but let's start out there nonetheless. And I'm gonna group six together as a category because we talk about these a lot on the Camp Geo app. You know, these are the typical ones. It's granite, rhylite, diorite, andesite, and gabbro basalt. Those six, can you I think this is fairly short, but what you know, what what are those? Why do they require short and brief, you know, dirty elevator pitch for 'em?
SPEAKER_00I think of those rocks as being a part of a family. You have the felsic family, which in in petrology you think of felsic as being light colored, rich in quartz and felds bar and so on. So granite and rhyolite are the felsic family. And then you have the intermediate family, where you have uh a pretty good mix of felsic minerals and some mafic minerals, and if you think back to Bowen's reaction series, it ties nicely into that. And then you have the mafic family with gabbro and basalt. That's the way I think of those. And and so when I talk about this with the kids, I'll I'll just bring them back into lab and I'll have a big box of like really good big samples, and I'll lay them out that way. I'll I'll put granite next to rhyolite, and then down below it, I'll put diorite next to andesite, and then I'll put gabbro next to basalt. And so you can see on one side, I've got them all lined up, right? Six rocks all lined up in pairs. One side is uh intrusive, slow cooling, one long, slow cooling, right? That's the typical interpretation. And that would be, you know, granite, diorite, and gabbro, and then the other side would be the extrusive version of those, and that would be then rhyolite, andesite, and basalt. So I'm like, you know what, guys, take your take your phones out and take a picture of it. It it's mentally that's just good organization, I think, for them to be able to see them laid out that way.
SPEAKER_01I would agree completely with that. And these are, I mean, granite rhyolite, these are the lighter colored ones, these are like grays to whites, pinks, something like that. Rhyolite can be a ton of different colors, but generally on the lighter end of the spectrum. And then diorite and andesite, these are the intermediate ones, these are the kind of salt and peppery ones. And then we've got gabbro and basalt. Gabbro can be salt and peppery, but you know, it's pr it's pretty dark overall, dark colored. Gabbro's a weird one in the field because the feldspar, the plagiarised feldspar, weathers to a really chalky white. So it looks really like black and white, checkerboardy kind of in some ways, but it's actually a really mafic rock. Anyway, so you kind of go from light to dark in those. And these are really I I think of these as kind of like the fundamental rocks of the earth, because granite is broadly the composition of the upper continental crust, the intermediate rocks, andesite and diorite, those are the composition of like the lower part of the continental crust and some parts of the oceanic crust, and then you've got gabron basalt that are the oceanic crust. I mean, the someaphic rocks, they're the oceanic crust. So this is like kind of the fundamental starting point of Earth's rock cycle, at least in my biased igneous petrology view of the world, right?
SPEAKER_00So, can I ask you a question though, about this? And so you would think, based upon Bowen's reaction series and based upon the way that you get granite is by just distilling rock after rock after rock, and you end up with more and more and more felsic. Then why from your perspective is diorite not more common? Because it's not a super common rock in the field.
SPEAKER_01It's not a super common rock in the field, and I think that's in part because well, so the average if we people who've tried to make chemical averages of the continental crust would say that the average composition of the continental crust is andesitic or diuritic. So we see a lot of basalt and we see a lot of granite on the surface. Right.
SPEAKER_00And there were two common rocks on the crust. Exactly.
SPEAKER_01The reason that we don't see diorite thought being is that diorite's all down in the middle of the crust, it's all down 10, 15, 30 kilometers down in the crust, and we just don't get to see that very much. And when we do get, like there are places south of the Sierra Nevadas, the Sierra Nevada Baffylith has been tilted. So you it's a preserved sort of cross-section of a subduction zone system, and you get a look down into the like the lower parts of the really the this crustal to what they call transcrustal magma system, 30 kilometers of a uh an active subduction zone system, and it's been tilted, frozen in place and tilted. And uh down there you get a lot of diorite, a lot of diorite at the base of these arbores.
SPEAKER_00It's just not a very common rock to see in the I agree.
SPEAKER_01It's really uncommon. You're much more likely to see gabbro than diorite typically.
SPEAKER_00So yeah, I see diorite, you know, when we go to Glacier National Park, there's that massive, impressive, you know, sill, this igneous intrusion that runs right through one of the upper layers of the limestone. And it's amazing, but it's just not very common. It's not very common.
SPEAKER_01So those six are kind of the framework, right? Granite rhylite, diorite anesite, gabbro basalt. Those are the the fundamentals. Now, I'm gonna jump a little bit around here, Chris, but we're still in the igneous category. I want to talk about peridotite, real quick, peridotite. We talk about this in the CampGo app in the igneous rocks chapter for sure, but what do you talk about with peridotite?
SPEAKER_00I think it's important to show my students peridotite because I talk about it from the context of all right, here's your look at the mantle. It's super important, layer the earth. Here's what it looks like. And you said that gabbro can, you know, look different in the field. You know, it's really a mafic rock, but it can kind of have that salt and peppery look to it. Even it's really mafic, typical, you know, really good lab specimen, when you hold it next to peridotite, then you can really see the difference between mafic and ultra mafic. And I think that's important to show the students, right? Is you think this is, you know, mafic? Well, look, look at this one right here.
SPEAKER_01And they're like, oh my gosh, this rock is dark brown and black and dark green, right? There's there's just there's no feldspar, there's no quartz, this is just pyrigene and olivine, that's it. That's a really important rock. And you know, those those are, I would agree, we include that in our you know, rocks they need to know in the pens in the um physical geology class I teach. There's one that's not on this list, which is comadite, which we talked about in the camp geo thing, which is the extrusive equivalent of prudotite. Well, kind of the it's it's ultramafic, but it's a lava, and it's not commonly talked about in intro courses, even though it fits this kind of family categorization you've made, it would be the you know, the missing part, the extrusive ultramafic rock in this this view would be number eight, but it's really only common from the very early earth, from the older than 2.8 billion, well, older than 2.4 billion years ago, I would say. And so it's just not one you come across in the field. So I think that's I'm guessing that's why it's not included in this this list.
SPEAKER_00I don't include it because it's very niche in in its setting, it's you know, it's geologic setting, it's not a very common rock. And the other thing is it's not gonna show up on Dr. Maddox's exam. Not to say that I I teach beyond what he's gonna throw at my students. My kids are exposed to way more. But that's just I don't know, you have to draw the line somewhere, you know. I teach porphyritic andesite, but I don't teach phonolite porphyry.
SPEAKER_01Right. Well, that in that but phonolite porphyry is a rock you're as a normal run-of-the-mill geologist or interested person, you're gonna come across phonolites a lot more than you're gonna walk across comadites. Comatites are a very, to your point, very niche rock, even though they fit this kind of categorization quite nicely. It does. Um, it's pretty niche as far as the the distribution on Earth. So there's a few on here, Chris, that uh I certainly don't cover because you know we only have a semester and we we have one lab on igneous rocks for these three here. And I want to know, I want to get your take on them, and which of these are kind of like personal interests versus possibly on the exam, or you know, why you cover these ones? Obsidian, pumice, and scoria. Why do you talk about these? I guess you you personally, I would say.
SPEAKER_00Okay, absolutely. Pumice is just an interesting rock. I it is pumice. Yeah, you you should because you know you were one of the most gifted students that I've ever had, and you you only I think you only got one question wrong on the Grand Valley exam, and it was pumice. And I'm like, really, Jesse? This is the I was staring at you. Um you are beating yourself up over this, but it was free response. The word I think just escaped you, which I I just don't understand because it's a gimme, it's it's a gift.
SPEAKER_01I remember exactly where I was sitting in that class. My memory, as you know, Chris, is horrendous, terrible. But I have a few bad memories that are imprinted that I, you know, you can just I just remember everything about it. I remember where I was sitting in that class. I remember the exam on the lab tables, rocks getting handed around, you know, you got a certain amount of time, etc. And then you, I think at that point you gave extra time. You could kind of go back to whichever ones you wanted a little bit extra time on.
SPEAKER_00And I sat there I just don't believe time should be a factor, so I give everybody the time they need.
SPEAKER_01So I had what five five minutes? Let's I'm making up a number, three minutes, something to to look at the rock, answer the as you said before, a couple questions. And I was just sitting there being like, I can't effing think of the word. I know exactly this rock floats, it's felsic, it's vesicular. I just can't remember the name of the rock. And then I I went back to it. You got two out of three points on it, yeah. Yeah, and you came back to me and you came back because you were like, anybody want any more time to go look at stuff? And I was like, Yeah, I gotta go look at this other rock. And you I remember you sidled past me and you're like, I think you said something to the effect of if you haven't remembered it now, do you think you're gonna remember it? And I was like, That was just probably not probably not good. It's it is the only thing I missed on that exam.
SPEAKER_00But so I teach pumice because it is a niche rock, but it's not uncommon. That's true. It's a tortured igneous rock, and it has that really tortured look to it. It's explosive, it's got a really cool story. I love pumice. You know, you and I remember walking across the pumice field at St. Helens, and we're punting rocks, and so cool. Like it's crazy, you know?
SPEAKER_01Yeah, I mean, pumice, so all these are lava-based rocks, right? They're a lot of they're glassy. Obsidian is very glassy, it's all pure glass, and I think people kind of know what obsidian is. We've talked about it all actually. We talked about it a lot in our in the Yellowstone, Geology Yellowstone audiobook on our Camp Geo app. We talked a lot about Obsidian and how it's such a valuable, you describe it as the MVP of rocks for for Native American communities, right?
SPEAKER_00Absolutely.
SPEAKER_01And and then pumice and scoria are just felsic and mafic varieties of vesicular. They have gas bubbles in them, very frothy magma that ends up crystallizing as glass. And I I agree, Chris, it's an amazing rock. I was just walking across scoria last year at uh craters of the moon. You know, you have all this these huge cinder cones just pop up and they end up having scoria everywhere.
SPEAKER_00And that stuff at Craters of the Moon, uh That blue dragon basalt. It has titanium in it and it oxidizes to this like peacock kind of look. It's amazing basalt. It's world class.
SPEAKER_01It's world class. So those three, I guess one thing I'm I'm genuinely curious about is how much of this do you teach in part because you know that you're gonna get a significant fraction of your geology students who go on the summer science trip. And you're gonna go to places like Yellowstone where you have tons of pumice and obsidian around.
SPEAKER_00That's not a thought. Oh, really? I don't think about that. No, I don't. I don't think about that at all. If I was gonna do that, then I would definitely add phonolite porphyry to my repertoire of rocks because we come across that at Devil's Tower. I have far more students that take my geology classes than I can take on summer science. Yeah, for sure. I know that. It's just not a thought.
SPEAKER_01Okay. All right. I think that covers the that's the igneous rocks you cover. And we're gonna, again, we're gonna talk about things like phonolite in another episode. We're gonna we're gonna save the rocks you don't necessarily need to know, or don't you don't necessarily need to know. Let me put the emphasis in the right place there, um, in another chapter. So let's move on to sedimentary rocks, Chris, which are back to our interpretations. I think sediments, to your point about it's not about identifying the rock, it's about identifying the rocks so that you can tell a story about the planet. These are maybe the most important, or sedimentary and metamorphic are much more useful in this category than igneous. Like igneous is kind of useful, but if you can identify a sandstone versus a shale, that tells you a dramatic difference, right? In the what the Earth was doing back in time.
SPEAKER_00Absolutely. The the the interpretation, the depositional environment is is very, very specific for these sedimentary rocks. I think that tells a beautiful story. I I just uh love that.
SPEAKER_01I guess my point is if if you get a rock and you you think it's a granite, but it's really an andesite, your geological interpretation of that difference isn't gonna be massive. You're not gonna be massively wrong about the tectonic setting. If you look at a conglomerate and you think it's a shale, you're gonna be way off in like the prior setting, right? So so on that note, I'm gonna kind of go through here conglomerate and brecia. These are the the big coarse-grained ones. I mean, these are typical, yes, in in intro classes, would you say? Are these typically I would hope so.
SPEAKER_00I I would hope so. Maybe maybe perhaps not Brecia. Breccia is spelled B-R-E-C-C-I-A. And the most common I ask my students when I throw that up on the screen and I say, what do you think? What what does this word sound like? Yeah. And they always say Brescia or Brescia or Brecia. Yeah, okay. Yeah, I that's been a recent one, Brescia. And I'm like, no, it's it's Brecia, like you betcha.
SPEAKER_01Oh, hey. That's a good one. I'm gonna steal that. That's a very good one. So you said something interesting there. I want to know why. You thought that Breccia might not be. Why do you say that? Might not be, you know, typical in igneous in uh introductory classes. Why do you say that?
SPEAKER_00I think Brecia is more niche in its environment of formation. You know, Breccia is just like conglomerate. We're talking about sedimentary rocks that have big pieces in it, gravel sized pieces and cobble sized pieces, and they're just they're big, and that indicates really high energy deposition, such as like a fast-moving river and things like hard deposits, right? Things like this that are very high energy. But Brecia, the pieces are angular, they're not rounded, and so you have a high energy environment, and there's just very little transport before deposition and then lithification. You know, we have some in the um in the upper peninsula of Michigan. As soon as you cross the bridge and you go into St. Ignace, you have this limestone collapse Brecia. And this is just where groundwater made little caves, and the caves formed sinkholes and busted up all this limestone, and then it got lithified right there in place. And so it's a beautiful rock. I love it.
SPEAKER_01It's a beautiful rock. I yeah. Breccia is just some of the coolest rock out there, I think. I mean, just two months ago, there's this amazing rock that's exposed around this sort of eastern Pennsylvania, down into Maryland, Virginia. That this sort of these basins, they're like 500 MA. These are extensional environments where there were obviously high relief created, and then basically these things just these down drop blocks formed. And so you have this breccia, but it's lithified by limestone. So it's a limestone breccia in its deep red, super oxidizing environment with totally cool sharp angular class. They're all different kinds. It's just an unit's like an alluvial fan deposit, just unbelievable rock. And it's amazing the exposure. Like you'll find there'll be a huge package of it, and then you know, 100 meters down the road, it's gone. Like it's gone from the sequence. You just lose it. Because it's this really, I mean, you think of this stuff like a cave collapse breccia, that's only forming in a really local environment. It's not forming over the entire continental shelf all at one time, right? This is a really local deposit. So anyway, okay, I'm rambling. Here's the point. The point is, Chris, is I'm I'm trying to tell our listeners we like sedimentary rocks. Sedimentary rocks are cool.
SPEAKER_00Yeah, they they absolutely are. And I think it's important to pair conglomerate and breccia together because then you can see, all right, well, these are both high energy because of the pieces that are in the rock. And that's the thing that I get I have to convey to my students. Don't look at the rock, you look at what's inside the rock.
SPEAKER_01Uh uh hold on, I want to double-click on that for the listener. This is a really, really that's a great tool right there for sediments. As soon as you identify it as sediments, go back to our how to identify rocks chapter. We talked about like, okay, you gotta decide is it igneous sedimentary or metamorphic? That's like the first thing. If you decide it's sedimentary, don't look at the rock, look at the pieces in the rock. I'm stealing that. That is a great phrase, Chris. Amazing.
SPEAKER_00And that's why, you know, hand lenses or little field microscopes can be super handy for this, because then you get to look at how these grains interlock with each other or the fact that they don't interlock. And that all of that is very telling in terms of well, what kind of rock am I looking at?
SPEAKER_01Oh my goodness.
SPEAKER_00Is this an you know?
SPEAKER_01So that's a good point you bring up, Chris. And I think, you know, we're gonna work through sediments here from high energy, large grains in the rock, to low energy. That's kind of the order we're working in here. So this brings us to the next set of two, and I'm curious about this one because this is one that, well, certainly I don't teach this to the intro to geology class. There's a sedimentologist who teaches another section, and she might talk about this, but I'd be surprised. We're talking about quartz sandstone and arco sandstone. Why do you well sandstone first, and then why do you why do you tease apart the differences in sandstone here?
SPEAKER_00Okay. So I need to back out of this just one more step and say that in lecture, when I cover just sedimentary rocks, I actually cover three sandstones. I cover quartz sandstone, which is well sorted, then I cover the Arco sandstone, which is only moderately sorted, and then I cover wacky sandstone or gray wacky sandstone.
SPEAKER_01So you cover the turnery, there's a sort of ternery diagram of sandstones. Okay. Interesting. That was one question. Is my question when I looked at this list, I thought, oh, this is really interesting. He's separating sandstone, but not into the traditional three. You're separating them into these two. So tease this apart.
SPEAKER_00Because wacky sandstone is very niche and there's not a lot of it. I don't have a lot of it myself. I don't have enough of it where I want to let my students destroy it in a lab. Because that's what happens, right? They just wreck rocks. Okay. And so I don't want to, I don't want to do that with them, but I'll uh here's why I tease them apart and and why I keep Arcos in the mix is because it gives me an opportunity to talk about sorting and what that means. Sorting, I don't know, for whatever reason, Jesse, can be a difficult concept, at least for my students. I don't know if it's an age thing, I don't know if you find this to be the case, but I certainly do. They struggle with it.
SPEAKER_01Yeah. Can I ask a quick question on that? Because I I teach this with regard to maturity. I kind of lump all of the sediments under this umbrella of maturity in a bunch of different categories where sorting is one category within there. But I think it's a really important point you bring up that sandstones, you're teasing this is the ability to kind of tease this apart. And so I'm curious about that difference. Do you have I guess what I'm thinking is do you have a a case study or uh an example? Do you talk about the Mississippi River? Do you talk about some setting that you know you can draw an analogy for this? Because I agree, it's a really hard topic. How do you get it across?
SPEAKER_00I use Skittles. I do. Of course.
SPEAKER_01Of course you do.
SPEAKER_00So here's here's what I did. I've only done it once. It was it was just this year. I actually woke up at two o'clock in the morning thinking about this, and I'm like, I'm on to something. This is a good idea.
SPEAKER_01So I went out and I let me go get me a big ass bag of Skittles. No, I I did.
SPEAKER_00I think I bought 15 pounds of Skittles. Okay. I bought three five-pound bags. Okay.
SPEAKER_01That's so good. So good.
SPEAKER_00The things that we spend money on as teachers is crazy.
SPEAKER_01So good. Oh my goodness.
SPEAKER_00So what I did is I I had each kid, you know, grab just a big old handful of Skittles. And then I had him grab an index card. And I'm like, okay, let's make red Skittles quartz, little grains of quartz, sand. Okay. And then let's make orange Skittles, feldspar, let's make blue or uh yellow Skittles, mica, Muscovite, you know, and so on. I so I I used like really common minerals and I assigned a color to a mineral, if that makes sense. So everybody was working with the same thing. So then I said, okay, well, let's just look at your pile that you have sitting in front of you, the this on everything pile of five different colored Skittles. Would you call that pile in front of you well sorted? You know, and you're like, no, of course not, right? Then I just kind of I walked them down a path of all right, well, let's take that pile and let's transport all of these Skittles down a stream. What's gonna be the first one that goes away? Like what's not gonna stand up, right? And so we removed things like biotite and muscovite because they're so flimsy and they break down, right? So remove those colors, whatever color I assign to those, get them out of there. So now I have a pile that is more homogenous than what I started with. And then I just keep working down, right? And I'm like, okay, well, let's move this several dozens of miles downstream even further. Let's slow the water down and allow deposition to take place. And now what do we have? And we're gonna be left with quartz and feldspar for the most part, the two like really most common minerals at the crust of the earth. And then I I'm given an opportunity to talk about what happens to what's the difference between quartz and feldspar? What happens to feldspar? Feldspar breaks down mechanically easier, but it also breaks down chemically and it turns into clay. I talk about all right, well, I have this pile of Skittles that I have quartz and feldspar mineral grains in it, sand grains. Is that well sorted? No. Is it poorly sorted? No. Okay, now you have an Arcos.
SPEAKER_01Yeah, yeah, yeah. Okay.
SPEAKER_00Okay, and then I'm like, all right, well, let's let's go ahead and take this downstream now a long ways and let's get all the feldspar out of there. All I have are one color Skittles. Is that well sorted? Yeah, that's well sorted. And so I use it. I I'm I'm giving you like the 10-second version of like a lesson. Yeah, right. If this takes time, yeah, for sure. Yeah, absolutely.
SPEAKER_01No, but that makes sense. I mean, that that really that's a good example, and I think I I could see the reason why you would have Arco sandstone and quartz sandstone. Uh, some people would call it aeronite, you know, quartz sandstone, aeronite sandstone, those are nite. Those are same thing, absolutely, same definition, basically. But and I could see why you would teach those and not the wacky sandstone, and some people would call that a lithic sandstone. And I always think of lithic sandstone as it has actual fragments of rocks in them, like the sand grains are little pieces of rocks, and that only really forms when you're like you're on a beach, you're looking at the ocean, you turn around, and there's a volcano right there. Like you have to be really close to sandwiches.
SPEAKER_00Or turbidite, you know, turbidity currents and things like this ripping down the continental slope and thin layers of sandstone in a big turbidite package or something.
SPEAKER_01And they're a very different setting, basically, than what you're describing. So I I what you're describing makes complete sense pedagogically to describe maturity by using these two sandstones. And that's a beautiful one. And I think it's an interesting, sorry.
SPEAKER_00It also provides me with an opportunity to like I have a lot of I have a lot of Arcos sandstone. And so to then say, look in the rock. What minerals do you see in this rock? Well, I see a bunch of salmon-colored grains that look a lot like feldspar, and they're like, Well, this is why we do minerals before we do rocks, you know. You're right on. You you, you know, so it's another then opportunity on a one-on-one or a one-on-two setting to say, look in the rock. Don't look at the rock, but look at the pieces that are in it.
SPEAKER_01I think this also I'm guessing, Chris, this brings you nicely into shale as well, right? Because shale's the next one. It's a dead obvious one. Like every class will teach you shale. You're gonna learn shale because it's you know such a big, important sedimentary rock. As part of this discussion, it brings up, I guess it answers the question: where did all the feldspar and where did all the muscovite and biotite go when it got weathered out of this stream sediment? Where'd it go? Right? And the answer is it's in shale. It's in clays that end up getting brought out.
SPEAKER_00Silicate minerals chemically weather into clay.
SPEAKER_01Exactly.
SPEAKER_00And so clay can be thought of in two ways, really. Clay can be thought of as its own mineral, and it can be thought of also as a grain size. And in the case of shale, it's really both. Dust size pieces. I associate the energy the particle size, the pieces that are in the rocks with energy. So conglomerate and breccia, big pieces, high energy. Sandstones are going to be moderate energy. The water has slowed down, and so the pieces that the water is able to carry and subsequently deposit are smaller. And then what's smaller yet? I don't get into silt stone, Jesse, because I just frankly don't have room for it. And it's kind of a it's it's this transition rock. So I go straight from sandstone, moderate energy, to really calm, quiet energy, which deposits shale.
SPEAKER_01All these rocks. You bring up a really good point about all these rocks, igneous, metamorphic sedimentary. There's gradients in between all of them. So we break them into categories because we have to, but if you look at the sediment size chart, got boulders and cobbles, there's a hard cutoff between those that is just a human, this is a human thing that's made up, right? These sized fractions, the borders between them are just made up, right? And so obviously there's a big gradient. Same thing for metamorphic rocks, same thing for igneous rocks. I mean, that covers shale, the really low energy, but it's still detrital. It's still pieces of rock, it's pieces of minerals. That's what we'd use as detrital.
SPEAKER_00Now, I one other thing before we move on, because I sense that you want to move on to the other kinds of rocks, but in my class too, in terms of shale, is I bring up a bunch of shale and and I have each kid come up to the front of the room and grab a piece, and we have shale communion. We we uh you know they all sit down, and I'm like, okay, you are free now to take a little bite out of a corner of the shale. That's funny. Because it's it's one of the ways that we do, we call it shale communion. And the shale that I'm using is some of the shale that I got from the gypsum mines in Grand Rapids a long time ago. Yeah, and and so this shale also has coprolites in it, which is fossilized shark poop. So I don't tell them that until after.
SPEAKER_01No, that's right. Yeah, you gotta save that one until the end. But it's gritty, you know, it's hard to feel with your fingers, it's hard to feel the grits with your your the tips of your fingers, but you can feel between your teeth.
SPEAKER_00Barely, barely. It's it's more chalky than anything else, and it also breaks really easily, which is one of the ways that I want them to it is. It's a weak, wimpy rock, and so that's why we bite it.
SPEAKER_01Okay, the next one I cover it for sure because I'm in Pennsylvania. I'm curious why you cover it in Michigan, is coal.
SPEAKER_00Oh, because it's so important, it has been historically so important.
SPEAKER_01So you just talk about it just because societally relevant rock.
SPEAKER_00Very relevant. I think a lot of people have seen it too. You know, everybody from Michigan travels south. So most of the people are gonna travel through the you know the Appalachian Mountains at some point, and they're gonna see these seams of coals. Or if they go out west and they go through Gillette, Wyoming, they're gonna see these massive seams of coal. And it's you know, that's what bounces out of all the train cars heading to to the power plant uh near the lakeshore.
SPEAKER_01Yeah, that no, that's a good point. I mean, I cover it because we're in Pennsylvania, and you know, heck, coal built America for many in many ways, right? I mean, the steel industry, the power industry, uh, you know, everything. So um I cover it because there's we're in Appalachia here. The next two limestone, I think that one I I don't have too many questions on. I mean, it's limestone, it's the big dog, it's a chemical precipitate, like you should know that. You covered Dolostone. Dolostone is also on here. That feels like it's I don't know, that feels like it's immigrant. No, no, no. You think so? Why? I would I would just put Dolostone in the gray area. I mean, coal, obviously, it's it's an important route to cover, but it's not one of the big ones scientifically. Dolostone's important, but I could see leaving it out too. So what's the rationale?
SPEAKER_00Okay, I I absolutely can see leaving it out, and I don't have to cover Dolostone, but I feel like it's a part of Dolostone is necessary in a class like this because it gives you separation. It's you have to identifying Dolostone is different. Okay, and I want them to experience that difference.
SPEAKER_01That's a great point. Just you know, saying, okay, limestone fizzes when you drop acid on it, dolestone, you have to scrape it to fizz, you have to get powder to fizz. Just that difference, is that what you're talking about? Like teaching them to be maybe a little bit meticulous.
SPEAKER_00Absolutely.
SPEAKER_01It is go one step deeper than the surface, you know, test.
SPEAKER_00Yeah, I you know, if you spend three weeks in lab identifying rocks and you go through this. I have what I think is a bulletproof protocol for identifying rocks, these common rocks that they have to know. They get into this habit of picking them up and they're like, oh, that's what it is, and they plop it down. Then uh you pick it up and plop it down, right?
SPEAKER_01For sure, for sure.
SPEAKER_00And they get into this routine really quickly. And and I think I I started doing this, and it's kind of touchy-feely, and you know, I don't know what you think about this, so I'm interested to hear this. But I started having them identify rocks with their eyes closed.
SPEAKER_01Oh, interesting. Okay, how does that go?
SPEAKER_00I want you to I want you to use your other senses, right? Because when you hold these rocks in your hands, Jesse, you and I, we've held so many rocks, they have a feel. Yeah, right.
SPEAKER_01You get even a sense of the weight, right?
SPEAKER_00You get it, you get a feel for density, absolutely the hardness, the sharpness of the edges of the minerals. Like we need to use more than just our sight when in identifying rocks. We need to use all of them. We can use taste for or like textural feel with in terms of biting some of them off and things like that, right? And and so, because I have samples in my lab that are quartz sandstone that look just like some of my samples of Dola Stone. They have this beautiful banding in them and so on. And if they just look at them, they don't know how to tell the difference. I'm like, well, wait, come on now. Gotta pick it up. Hold it in your hand and rub your thumb over it. Which one feels like sandpaper? And that's a textural thing. You don't need your to identify that.
SPEAKER_01You know, the difference, and and this is like a I think some other science fields and some other scientists sometimes look at the terminology we use in this mineral and rock identification thing, and they're like, what the heck are you doing? But the difference that you're describing there is gritty versus waxy. And those terms, you might be listening to this and think, what are you talking about? Gritty, waxy in a rock. But when you rub your finger across it, you know the difference. You know the difference between sandstone and sandpaper grittiness and that dolostone or marble y waxiness to it. It's just a little bit smoother, it's a little bit kind of a greasy feel to it, right?
SPEAKER_00And that's that's right. And think about holding limestone in your hands, right? Limestone can be a difficult rock, it's the Katy Perry of rocks. We've talked a lot about that before. It has so many different looks, but you know what? When you hold it in your hand, limestone is made up of calcite. Calcite is a soft mineral, it is a hardness of three on most scalar hardness. Look, you can feel that if you hold it in your hand enough and you're using your other senses, you're not going to think that it's something else.
SPEAKER_01I agree completely. And this is what makes geology an inherently descriptive science. Science. Saying the rock is waxy is a very non-quantitative. It's not a scientific term because you have to be specific. And but ultimately, this is descriptive. And if you feel a waxy rock, you know it. It makes sense, right? So there is some aspect to this particular version of physical science that I think attracts people like me, and I think you, Chris, too, is something that attracts us to geology is this historicalness to it, this sort of descriptive storytelling nature to it. And we're kind of getting into that part of it right now in these descriptions of rocks and the differences here. So I actually really like that exercise of close your eyes and identify the rock because it tunes you into these things that uh you might not pay attention to. Like your students, if you're taught if you Chris Bull His are lecturing and say, hey, this feels waxy versus this feels gritty, those are just words that kind of go in one and you're not the other, I bet, until they have to do your exercise of close their eyes and and identify it, I bet.
SPEAKER_00And until I'm standing right in front of them, I'm saying, wait a minute, close your eyes now. Give me both hands. And I plop one rock in a different rock in each hand. And I'm like, okay, well, now tell me what you feel.
SPEAKER_01That's a great use your other senses. That is a a great exercise. I I like that a lot.
SPEAKER_00And I think that's that's a beautiful thing. That's the way science should be. Science should be hands-on and it should be using as many of our senses as possible.
SPEAKER_01Totally. Agree completely. Okay, that's Dolostone, limestone. I don't really have many questions about sort of what you don't cover in the sediments, but I do in the metamorphic rocks. So maybe let's move to that. And I think, Chris, we can probably move pretty quickly through the ones you do cover because they're these are the bog standard metamorphic rocks. So do you agree with that? Like, I don't know. Maybe I'll just list them and we can kind of talk about them.
SPEAKER_00And the order is list them in an order that makes sense, though. You know what I mean? You know what I mean when I say that. Yeah, for sure.
SPEAKER_01So I'm gonna go from low grade, quote unquote grade to high grade, meaning low metamorphic intensity to high metamorphic intensity. And that goes, well, there's two categories, two flavors, two families of metamorphic rocks. There's the foliated ones and the unfoliated. I'm gonna focus on the foliated ones, the one that have, if you pick it up your hand, you'll feel banding in it and stuff. Low grade is slate, higher grade is phyllite, higher than that would go to schist, and then the highest would be nice. And we kind of I think it's pretty clear, more intense metamorphism. It kind of stands out, Chris. Would you agree with that? That like going through those rocks, you look at them or you close your eyes and feel them and you feel more metamorphism, is that right or not?
SPEAKER_00I think so. These lower grade metamorphic rocks like slate and and even Philite, they just don't look sedimentary anymore. Their parent rock is sedimentary, you know, like slate, the parent rock is probably gonna be shale. And so if shale is made of clay, but if you subject that to low grade heat and pressure, the clay minerals they recrystallize into mica. And mica is this really beautiful, everybody knows it's the one that my kids love to destroy in lab, they peel it apart into thin sheets, you know. I just leave a mess all over the place. But actually, in the case of slate, slate has a glossy sheen to it because these are microscopic.
SPEAKER_01Let me interrupt real quick. It just the difference that I say is shale. If you pick it up and you tap it against the table, like tap it against the edge of the table, it's gonna break, it's gonna start flaking off, breaking apart. If you take slate, slate won't if you're just tapping it. If you hit it a little bit harder, a little bit more force, it'll start to break. Phillite will not if you start to hit it a little bit harder, right? Phyllite's actually kind of hard to break. So that kind of goes like, are you tapping it? If it breaks, it's still shale. If it doesn't break, then it might be slate. If you tap it hard and it breaks, it's probably slate uh and not phylite. And you know, it's just that they're like slightly better put together, I guess. Slightly bigger than it's a lot of things.
SPEAKER_00And another thing, too, about Phyllite, Phyllite's a beautiful rock, by the way. You think you and I both are in love with Philite. It's also this is subjective, but it's glossier. Yep, it is totally slate.
SPEAKER_01Definitely is.
SPEAKER_00You know, and it has this really and it's really easy to see when you hold them next to each other. Right. Absolutely, yeah, yeah, yeah.
SPEAKER_01And then we go to schist where we actually get to start to see mineral grains popping out. There's if you see garnets in it, it's usually a schist. We love schist. Uh, we have some actually, Chris. You know, do you remember the Starlight Schist we collected in the Black Hills?
SPEAKER_00Starlight Crosses, that's right. Beautiful.
SPEAKER_01So I have a piece of this. I'm excited about this. I'm excited for you to come visit Pennsylvania because you get to see this. I have a big piece of this. I mean, it's probably a meter and a half long. It's kind of like a needle-like one, which one face has beautiful starlight crosses in it. I've never really known what to do with this rock because it's kind of Wasn't that with you when you got it? Yeah, yeah. And you have you have a similar, a similar piece. Um, I think you have it kind of standing up as a column in your yard, if I remember correctly, like uh in this beautiful Starlight Cross is just on one side, and the other three sides are kind of crappy. So I've uh I've decided I'm gonna make uh an end table out of this where I'm gonna cut the bottom off of the Starlight Cross, and it's gonna be standing up, and then I'm gonna have a piece of wood, a single piece of wood, a side and a top that I'm gonna join together in a 90-degree, and then I'm just gonna set the wood on top of the stuff on the schist. And so the schist is gonna kind of be the base for the table and poke up through the table a little bit, and then have this like nice wood top on top of it with the colour. Well, that's a really good idea. It's gonna be totally cool, I think.
SPEAKER_00But I'd be nervous about cutting it only because the foliation makes it like difficult, it's true, kind of nuanced to cut.
SPEAKER_01That's true, and it brings that back to our point here is that schist is not the highest grade rock, it's still foliated, it still can break. Um, you know, the grains are pretty well put together, but it can certainly break. And then gice is when we start to get light and dark mineral segregations. I love gneisses because that's what I work on, but they're they're higher grade, more intense metamorphism. Those are the foliated ones, those are the four. Slate filite schist, gneiss. The unfoliated, the non-foliated rocks are marble and quartzite, and those are just really simple. I mean, marble is metamorphosed limestone or sometimes dole stone, but it's just recrystallized. The grains don't orient themselves, calcite doesn't orient itself, so it just is solid, big, beautiful rock. Quartzite is just metamorphosed sandstone, the quartz grains are just interlocking now. Um, and it doesn't have that gritty feel. Yeah, it doesn't have that gritty feel, it kind of chips. It's got a chippy feel, not a gritty feel, is the difference.
SPEAKER_00So, what are your questions then?
SPEAKER_01Well, let's cover the last because I know you have a few. Let's cover the last one, number seven that you do cover. You brought it up right at the outset is meta-conglomerate. Okay, you said I think you brought up a really good point. Metacongglomerate is as the name implies, metamorphose conglomerate. You said that it might be on the exam because it's common in Michigan, which I think is a really good point. And you and I have spent a lot of time looking after some metaconglomerates, digging around in gravel pits.
SPEAKER_00Oh, yeah. Yes, we have. Absolutely. Yeah.
SPEAKER_01How do you teach metacongglomerate?
SPEAKER_00It's really, to me, I think it's self-explaining. It was a conglomerate. That was the protolith, that was the parent rock. And then it got metamorphosed, heat and pressure, and it turned it in. So we call it a metaconglomerate. It's it's more colloquial, I think, to refer to it that way. Or don't you think, right? With we do the same thing with meta basalt, you know, with this these like low-grade chlorite schists that we see all over in the UP. And yeah, I don't know. I I that's how I kind of talk about it. I think that's if that makes sense.
SPEAKER_01I think that's probably right. And I think you're right, it's very common in Michigan. And it because there's huge swaths of metacongglomerate up in Canada, just north of Michigan, that got swept down by the glaciers. Pudding stone. Is people have heard the term pudding, like P-U-D-D-I-N-G stone, pudding stone. It's a meta-conglomerate. It has chert, has cobbles in it, and that's what you and I have sort of looked at or looked for quite a bit. It's a common rock in the Midwest. Oh, it's a stunningly beautiful rock, but it would be technically a meta conglomerate. Um, so the okay, the the questions are the ones that are not on here that I actually spend a decent probably too much time talking about in class are things like eclogite and blue schist. I don't know. What's the what are your thoughts? Why do I not have those? Yeah, or just like what are your thoughts on it?
SPEAKER_00Is it is it too in the weeds or no, no, no. I don't think so. Uh so I have some thoughts on this actually, but no, I don't. And if you tell me, Chris, you need to add blue schist and eclogite to your sets, then I will. I I absolutely will. But you know, Jesse, like uh tell me what you think about this. But a lot of intro geology textbooks, like the textbook I teach from. Well, I'm I'm not a book teacher, but I use the book.
SPEAKER_01No, you're definitely not a book teacher. Yeah. Uh see above, we created our own book in the champ GF. That's absolutely true.
SPEAKER_00Absolutely. Yeah. But Jesse, they don't touch upon ecologite and blue schist and the importance of them because I I they're really important, but they teach kind of these regionally metamorphosed rocks a little bit wrong. And this is is something that you and I have been touching upon in in recent episodes. Is it too soon to talk about this stuff in an introductory level class, right? I does that make sense what I'm saying.
SPEAKER_01Uh it makes complete sense. And something the way you just phrased that really struck me. You described it as like teaching these regional geology or regional metamorphic rocks, being meaning slate philite shist nice, like regional metamorphism, basically. And there's something amiss teaching that as a process because those those names, the way those names are derived, they're just textural. Whereas granite is a compositional name, granite has a composition embedded in it. Granite means it's got quartz and two felt spars in it, and it's a light-colored felsic igneous rock. Like that's embedded in the name.
SPEAKER_00Well, kind of it does though, because in order to get this really embedded foliation in these rocks, you do need to have differential stress.
SPEAKER_01That's true.
SPEAKER_00You need a directional pressure, so it does tell something tectonically that is important.
SPEAKER_01That's a good point. I think what I would love, and I understand well, I I partially understand why this is taught the way it is and not the way that I'm going to propose here. But I I wish that we embedded a little bit more process into the metamorphic rocks that we include here. Like what I'm thinking is isn't it much more important to know that an eclogite is a subduction zone system rock? Like it only forms in subduction zones. And a granulite is a rock that has had melt. It's been metamorphosed to such a degree that it's lost 30% of what it used to be to melting. And it's it's it's lost a granite and now it's a granulite. Like, isn't that a isn't that a more I don't know, a process-based way of teaching these things a little bit? Like I so I I don't know.
SPEAKER_00It is a hundred percent. I I agree with you a hundred percent. I like this. So two thoughts on this. One, I don't teach those rocks to my students because Dr. Maddox does not have them on the exam. You know, and and I I feel like I already have a lot.
SPEAKER_01Oh, you do, yeah. I mean, you have more than I let me just frame this. I don't teach the the Penn State class this way. I'm because again, we you know, there's a I teach a class that the engineers, the mining engineers, need for accreditation. So there's a certain skill set that I have to sort of teach to. There's a certain credentialing that I have to teach to, right? And everybody in the Penn State system has to teach to that. And so we're kind of bound by these the structures that are in place, the sort of quote unquote traditional thinking on this, I would say.
SPEAKER_00But I think it is also it's really ingrained in intro-level geology that it is slate, philite, schist, and nice, and sometimes migmatite. Yeah, you know, it's just like that is typical subduction zone, convergent boundary, lots of heat, lots of pressure, and it shows you grades of metamorphism. And I think that's what we're talking about. So, my second proposal, uh, and you don't know what I'm gonna say here, but I'm serious about this. We're getting long in the tooth on today's episode anyway. Why don't we record our next episode to be an episode devoted to how we think teaching metamorphic rocks should change?
SPEAKER_01I I think that's a good idea. I think that's a good idea because as you said, the typical way there's some major flaws to it. For instance, I don't see I'm an igneous petrologist, you know, I love igneous rocks. I don't see a ton of major flaws in the the list of rocks that you teach, for instance, or I teach. I teach them.
SPEAKER_00Maybe the interpretations are gonna need some tweaking over time, but yeah, that's right, you know, because we had this interesting discussion with Mike Axerson.
SPEAKER_01You know, but but those are the rocks, those are the important rocks. Metamorphic rocks, I uh there's definitely some tweaking that could be done there. Sedimentary, uh, you know, that's those are the basic sedimentary rocks. Those are the important ones, right? And importantly, let me just go through the list here again. Igneous rocks are granite, rhylite, diorite, andesite, gabbro, basalt, obsidian, pumice, scoria, and peridotite. If you know those rocks, you know the vast majority of processes that occur in the igneous processes of Earth. The sedimentary rocks are conglomerate brecia, quartz sandstone, arco sandstone, shale, coal, limestone, dolostone. If you know those rocks, you know most of the sedimentary processes, at least at the intro level. You know the sedimentary processes that matter. The metamorphic rocks, gneiss, schist, phyllite, slate, marble, quartzite, metaconglomerate. I would argue you're missing about five key processes that occur in the metamorphic system of Earth. And I would agree with you. Even though those are really important rocks, I we might be leaving out some really important processes that we could add color to in the intro by by just place replacing a couple of these. I'm not sure.
SPEAKER_00Well, let's do it. Let's do an episode, let's do a follow-up episode on on metamorph how we think the teaching of metamorphic rocks needs to change.
SPEAKER_01You know what, Chris, this sounds like another late night record with a whiskey and get a little rambly and just philosophical about it because we don't know. I like it.
SPEAKER_00Well, I think we do know. I think we do know, actually. Just not enough people ask us what we think.
SPEAKER_01Well, here's the deal. This is our podcast, so we say what we want on it. This is this is our time to talk now. Um you got that right. I I think that's right. And I think you know what, Chris, at the end of that, we're gonna make a lot more work for ourselves because we're gonna have to go back and re-record the metamorphic chapter of uh the Camp Geo book and or at least add to it, right? Add to add some color to it.
SPEAKER_00I don't know. We did though. We did talk about blue schist and eclogite and I certainly did. We did justice to that.
SPEAKER_01I think we're gonna end this discussion. Like, I'm kind of feeling this right now with this whole discussion is I want to talk about more. I want to talk more about igneocks. I want to add it sucks to teach, and okay, let's end with this question. Here's the 25 rocks you teach. We just listed them. 25 rocks that Crispalize teaches, the 25 rocks that you need to know as a basic intro-level geologist going out there. What are some big things you feel like you wish you could talk about more? What rock types? And we can save this for another episode because we're getting, like you said, long in the tooth. But what's the one rock that you wish was added to this list?
SPEAKER_00See, I don't know if I could answer if I had two, I would probably say eclogite and blue shist. Okay.
SPEAKER_01Because those properties are two. Yeah. Is there anything that that is just like a a wow factor, like a oh, that's cool factor that would like rope students into geology by I think so.
SPEAKER_00I think that and this is the difficult part. You know, we're kind of branded rocks for jocks. You've heard that before, I'm sure a lot. And or why do we need to know?
SPEAKER_01Just to explain that, that that is uh that's a reference to geology being the cheap, easy science that the athletes or the kids who want an easy science class, aka the jocks, take geology because it's the easy science credit. So that's the the sort of source of that term.
SPEAKER_00And maybe that's a bad reference, but it's out there. But uh I get this more with freshman level high school students where they say, Why do we need to know rock? I don't encounter that with my geology class because it's elective, and so most of my kids are there because they want to be. But we need to do a good job of like it's not identifying the rocks. We need to be able to identify rocks to be able to interpret the planet that we live on. It's just a big part of it, and and I love where we live. I think we live in an amazing place, it's so beautiful. The rocks tell the story. How can that not be exciting? I I just don't understand. And so that's the wow factor for me is is like just being deliberate about making sure they don't allow themselves to slip in the routine of I'm just naming rocks, I'm naming rocks, that's all I'm doing.
SPEAKER_01No, that's right.
SPEAKER_00I you know, there's a point to this.
SPEAKER_01Yeah, I think that's I think that's wise. I mean, what comes to mind for me is something like I wish there was an extra lecture in my class or something to to talk about something like I'm just thinking on the fly here, I think like banded iron formation. This rock where you look at it and you're just like, holy crap, nature can actually produce something this beautiful. Like that to me, that's just a it's an unbelievable rock, and it's amazing that the natural world creates something that pretty. And so I that's kind of like a hook, you know, for for intro people who are taking the class for the easy science credit. It's maybe a way to kind of hook them and say, look at this, this is cool. We're gonna talk about how nature makes rocks that are this beautiful. I don't see a reason why you could not carve that out as a part of your class because it's also one of the most important things for humanity because I already spend 30% of the class talking about igneous rocks, which is way too much. So, you know, I I run myself out of time by blathering on about igneous rocks for too long. But uh, yeah, no, uh, it is it's a it's a super important rock. But that goes into the category of rocks you don't need to know. We'll talk about that later. But here's the ones, let me just list them for the end here, Chris. The rocks you need to know, the 25 rocks you need to know: granite, rhylite, diorite, andesite, gabbro, basalt, obsidian, pumice, scoria, prritotite. That's the igneous rocks. The sedimentary rocks are conglomerate, breccia, quartz sandstone, arco sandstone, shale, coal, limestone, dull stone, and rounding it out with metamorphic rocks, nice schist, phylite, slate, marble, quartzite, metaconglomerate. That's a heck of a good list, Chris. I mean, ultimately. We have some, you know, we have a room for improvement. There's like gray areas here. We could pick, we could take things out and put them back in. But I mean, if you know those rocks, you're gonna be a very you know well-functioning geologist out there.
SPEAKER_00So I think so. It sets you up for whatever you have coming down the road. Absolutely.
SPEAKER_01I agree completely. Hey, Chris, that's a wrap. I mean, we'll talk about the rocks you maybe would want to know, but don't need to know later on. And let's talk about this metamorphic rocks thing. This would be super interesting. You can follow us, go to our website, planetegeocast.com. You can support us. There's two ways to support us. We appreciate both of them. The first is go to the first link in your show notes. It's the Camp Geo app. Listen to our free physical geology course in audiobook form. You can also purchase audiobooks on the geology of Yellowstone and the geology of the Grand Canyon and Earth's climate. You can just go to the first link in your show notes, download the Camp Geo app, and you'll get access to all that stuff. You can also head over to our website, planetgeocast.com, and there's a support us link. Send us an email with any of your questions at planetgeocast at gmail.com. Cheers. Peace.