The Geology of Clay
[00:00:00]
Okay, we're recording.
Chris Bolhuis: All right.
Well, that's good. that's good. to know. Thanks. I appreciate that. Otherwise I might've said something inappropriate.
Dr. Jesse Reimink: Puffy Vest Day, man.
Chris Bolhuis: I don't have a, this is not puffy.
Dr. Jesse Reimink: Oh, mine's not either, but it, you know, it's a little puff. it's not
Chris Bolhuis: got a little bit of,
Dr. Jesse Reimink: it's not, uh, flannel or, any other material. It's [00:00:30] a little bit of, there's a
little puff to it.
Chris Bolhuis: You, you, you're too preppy to be a geologist. Actually.
You're, you're a
Dr. Jesse Reimink: No, this is what it is, Chris. This is back in the day when the gentlemanly scholars were geologists, and they'd go out with their little bow ties on and their suits and walk around the
field and, you know, take their pocketbooks and their maps and their pocket
Chris Bolhuis: You know, those days are long gone. It's like the, uh, the old football coaches, the pro coaches, you know, they used to wear, suits and ties and not
Dr. Jesse Reimink: I was watching the NBA playoffs and, uh, yeah, there's not many coaches that dress up [00:01:00] anymore
these days. It's all sweatsuits they just kind of all blend in now. It's good. I mean,
Chris Bolhuis: Yeah, they caught on. They caught on. Smart.
Dr. Jesse Reimink: That's right. Um, what do you got for me to make me laugh today, Chris?
Chris Bolhuis: Oh. Wow, you can't do that. You cannot put me on the spot like
that. Um, I don't know. Yeah, we know we had kind of a serious more of a serious conversation before you know We really didn't come in laughing like we always do
usually I say something that gets you going and then you're like, okay I'm gonna hit record.
I
Dr. Jesse Reimink: [00:01:30] uh, we've got a lot of business to take care of. We've got a lot of stuff on the go right now. We got Grand Teton's audio book that's coming up. It's going to be released right around the same time as this episode. Probably. we're got an app update. We're doing a bunch of stuff this summer.
New Planet Geo episodes. You're planning trips. I'm planning a trip or two. I mean, we've got a lot going on, so
Chris Bolhuis: I thought about it yesterday though, I was on my tractor, and I thought, ooh, I need to have Jenny get a picture of me and my new tractor. hauling, hauling wood,
so,
Dr. Jesse Reimink: do need a picture of Chris on
Chris Bolhuis: do it.
Dr. Jesse Reimink: Ah, man, we gotta, gotta [00:02:00] get that. We gotta get that out there, into the world.
Chris Bolhuis: Alright, Alright,
I'll make work of it.
Dr. Jesse Reimink: so, This episode, Chris, this comes from Christopher Bolhuis.
And I'm curious about this because in your class, I don't remember this aspect of your class of, you know, me being a student in your classroom. this kind of topic, I don't remember. There's a few things I remember, but you know, me, my memory's terrible. And it was frankly, length of time ago.
Now that I was a student in your class, we don't really want to talk about that. Um, But this, [00:02:30] the kind of intro here is the geology of clay, and clay is a word that we use in a lot of different scenarios as geologists. So, what do students, when they walk in the door, think clay is? And then what do they think clay is when they, leave your class, I guess?
Do you, think you do a good job of teaching them what we use clay as? I don't know what that, that question is kind of like, how confusing is this?
Chris Bolhuis: Yeah.
I just got this question actually. And that's where this episode comes from is, you know, a really bright. Young student [00:03:00] says, Mr. Bolhuis, I, I need some clarification because sometimes you talk about clay and you seem to be talking about minerals, like a mineral group. And then sometimes you're not, you're talking about clay as something else.
And it made me think, This student was absolutely correct. I, there's some confusion in this. I think it's pretty pervasive actually, because we do this all the time in geology. I don't know why we just well, let's set the stage. Right.
first of all, we think of clay.
in geology, [00:03:30] like an intro level geology class. And we talk about it in two ways, one as a sheet silicate. It's a group of minerals and, everybody knows the micas, muscovite and biotite. And then Jesse, you and I love, love a bunch of other,
you know, micas like fuchsite and Lapidolite.
Dr. Jesse Reimink: Oh yeah,
Chris Bolhuis: you know, Phlogopite.
everybody thinks of those as the quintessential sheet silicates and they are. Clay is also a sheet silicate. It's a group of minerals.
And so we talk about that a [00:04:00] lot, but then I'll switch it up sometimes in the same class and talk about clay, not as a mineral, but as a particle size
so
we do this in our heads, like, because for us, it's so second nature.
We just flip this around and without being deliberate about first explaining that and
then, letting them know that I'm, we're switching gears here. We're talking about clay as a different thing. Now,
Dr. Jesse Reimink: The naming system in geology, this is one of, I mean, we give biology a hard [00:04:30] time, but the biologists, one thing they do do better than the geologists is naming schemes. I mean, just having, you know, the species, genus, you know, that whole sort of Latin rooted naming system is so much better.
Geologists are terrible at naming. If you've ever tried to learn rock names or mineral names, They're all named for like, some random location somewhere, where it was first discovered, or some random person who discovered it, or some other random fact about the thing. So, we don't have a systematic approach to that, and clay is one really, I think [00:05:00] obvious and, and uh, introductory example of that.
So like, you'll, you'll run into this clay naming problem. At your first exposure to geology, really. And then the other problem is that society uses clay in different ways as well. Like when normal people who have no geology exposure think about clay, they probably think of, a layer of clay in the soil, it's a material type, right? It's not really a grain size or it's not really the minerals. It's like some, it's a material. It's a thing, right? Where you put
Chris Bolhuis: something that you play [00:05:30] with, is what I
Dr. Jesse Reimink: something you play with, right? Or you make pottery out of. We'll have an episode talking about the geology of pottery clay later on because we've had some listeners ask us about this and ask us that question.
But, you know, Colloquially in society, clay means one thing. Then as geologists, we have two different, very specific definitions for clay. And those are the ones we're going to focus on today, Chris. So just to summarize, again, we're going to talk about, the size definition of clay.
And then we're going to talk about the mineral of the clay, as you said, group, the clay group of minerals. We're going to cover those [00:06:00] two geological, meanings of the word clay.
Chris Bolhuis: Okay. So let's go ahead, Jesse, let's get into this like particle size definition. And again, we're keeping this, you know, sed strap people, sedimentologists and stratigraphers, they, they would listen to this and they would just roll their eyes at like, really, this is the level that what you're going to do,
Dr. Jesse Reimink: Let me interject real quick, because the engineers use this definition of clay, this size definition of clay, a lot too. anybody who's doing geological engineering, they mostly use [00:06:30] clay for this size definition part too. it's commonly used, but it's very introductory level.
Like, this is
super, super basic level stuff. So,
sorry.
Chris Bolhuis: Well, well, no, just a little background on that. You get a lot of engineering students in your introductory
level class. And so That's why you would know this, right. You, these, these people, they, they have to take this class, right.
Dr. Jesse Reimink: Yeah. So a lot of them are for a mining engineering degree. And so they require my intro level geology class. So that's exactly right. [00:07:00] Some civil engineers too, who also require this class as well.
Chris Bolhuis: So particle size, a millimeter is about the thickness of a dime. Okay. If you lay a dime flat on a desktop, that's approximately a millimeter. A clay particle is one two hundred fifty sixths. Of a millimeter. So we're talking about a very tiny, almost microscopic particle. and it has nothing to do with composition.
This is straight up particle size. [00:07:30] So
one 256th of a dime's thickness,
or.
Dr. Jesse Reimink: It's
Chris Bolhuis: Yeah, you know, I have, I got a bunch of pencils on my desk, those mechanical pencils, and all of mine are 0. 7 millimeters.
A clay particle is smaller than 0. 0039 millimeters. so you think of the sharp point of that mechanical pencil, and it is a fraction of that.
I mean, it's, it's, It's
so It's a tiny.
tiny
[00:08:00] particle. So why is this important, Jesse, for geologists to classify a particle size in this way and refer to it as clay? Why? Because it is a really important thing.
Dr. Jesse Reimink: so the reason that it's important is because we, when we talk about sort of soil properties or sediment properties, we use naming systems that are dependent upon the grain size. So, you know, when we talk about shales or limestones or [00:08:30] sandstones, the name is a confusing name.
Shale it doesn't relate to this feature, but what we mean by shale is fine grain sediment and shale often has a lot of clay size. So the name of the rock or the category of the rock, the rock type is telling us what the grain size is in the rock on average. And these, these range wildly, but we break these apart because we kind of have to have a classification scheme.
We can't just say sediment. Sediment is. It could be anything. It could be boulders, or it could be tiny little particles, we need to break it down. We need to say clay sized sediment is [00:09:00] a very different beast than a boulder rolling down a mountain stream. we have to be able to distinguish those two when we're talking about geological processes.
So that's why we have this, this thing.
Chris Bolhuis: because what we're trying to do is reconstruct the geologic history or the geologic story of the rocks that are in front of us. Right. Is that a good way of
Dr. Jesse Reimink: That's exactly right. So if I, so Chris, if I say, Hey, you know, there's some sediment that is piling up somewhere in my backyard. back to the engineering thing, if you say, Oh, there's some sediment piling [00:09:30] up, how do I deal with it? You're going to be like, well, is it boulders or gravel or clay? like, what size particle are you talking about?
What is the sediment type that you're dealing with? Then we can talk about how to deal with it And so. Just to frame this, Chris, people have probably seen this. If you have a, like a right in the rain notebook the right. in the rains have table in the back, that is a grain size table and clay is the smallest grain size here.
So it's less than you said, 0. 0039. It's very small. It's the smallest grain size. Then we go, as [00:10:00] we get coarser in grain size, we go silt, then sand. than gravel. Those are the typical categories. and those silt, sand, gravels, they have like fine silt, medium silt, coarse silt, right? So subdivide these categories, but that's
the general ones are clay, then silt, then sand, then gravel and then we can get boulders, etc.
above that.
Chris Bolhuis: that's right. And for us, that's really important to know because water is very discriminating in terms of what water is able to carry in terms of sediment or [00:10:30] particle size is directly related to its energy. So,
only high energy and fast moving, like mountain streams, that's able to move gravel sized particles quite often, right?
And so all the smaller pieces, they get swept downstream. it's too much energy. It's not a fast moving mountain stream is not going to allow a lot of sand and clay sized dust sized pieces to settle out. So they will get swept further away, [00:11:00] leaving behind them only these bigger, heavier, coarser gravel sized pieces.
Then further downstream is the water slows just a little bit more. it doesn't have much gravel left in it. And so it's slowed down now, maybe it's slowed down enough to allow sand to get deposited. And then the dust and the clay size pieces, they get swept further downstream until it's like really super, super calm.
And finally the dust sized clay size pieces can settle out. So that gives [00:11:30] the geoscientists, a really good indicator of, is the rock I have sitting in front of me. This is how the conditions were changing then at this particular location.
we talk a lot about this and Jesse and with our shifting shorelines,
you know, we came up with a, a, really good animation for this how you get these vertically stacked sedimentary rocks in one location.
It directly relates to the shifting of the shorelines. Where is the high energy shoreline? And, it [00:12:00] progresses offshore into calmer and calmer and calmer waters.
Dr. Jesse Reimink: there's something just popped into my head, Chris, as a sort of an example of this. And so, I mean, when we're talking about rivers, let's, ignore the mountain stream for now. Let's talk about a river that's maybe meandering back and forth. We drive past these all the time, the Susquehanna here up in Pennsylvania.
you think about that river, think about a nice clear water day, it's kind of flowing over the rocks and stuff, there are rocks in the bottom, those rocks are not moving. The rocks rarely move except in flood stage. sand [00:12:30] actually very rarely gets lifted up and suspended in the water column, like sand moves by being what's called saltation, it bounces along the bottom, it gets picked up by a little eddy current and dumped off really quickly.
It doesn't have a really big eddy. Make it into suspension. Now picture that same clear stream or clear river after a big rainstorm. It's going to be muddy, right? It's going to get muddy water there. And I think people have probably seen these images of two streams merging together, one, which is really muddy and one, which is clear or like, [00:13:00] streams going out into the ocean.
Actually, I just saw one, Chris, from, uh, Holland or Grant or Muskegon, I can't remember
which one it was. of the
Chris Bolhuis: the
yeah. Where the Grand River dumps into Lake Michigan, It is
Dr. Jesse Reimink: Yeah,
Chris Bolhuis: a distinct line.
Dr. Jesse Reimink: such a distinct line, but you have this kind of muddy water flowing out into this clear, beautiful Lake Michigan, and that muddy water doesn't immediately mix.
And it's because it has clay in it, right? It has these clay sized particles suspended in it, and that water is moving enough to carry the clay. And I, I don't know, I experienced this, I'm kind of like [00:13:30] Chris with, rocks saw that I have like it, cuts rocks in the oil and the bottom when you're cutting, it gets stuff suspended in it.
And then over time, that stuff settles out If I don't use it for a couple days, mineral oil will get clear because the little fine flower size particles will settle out. And that is geology in action. When we go look at a shale, you kind of feel it between your fingers or you can't feel grains or you feel between your teeth, you can maybe pick up some grittiness to it.
that means that, that had to be deposited in a calm, [00:14:00] calm water environment because otherwise those little tiny flower sized particles would be suspended in the
water column with Any
Chris Bolhuis: is gonna keep that lifted up. I kind of think about this way, you think of like baking flour. Each little particle in baking flour is about the size of a clay sized particle. Right.
if you take a five gallon bucket full of flour and dump it into a swimming pool, it's gonna turn at milky white,
you know?
But eventually those little tiny particles will settle down and the water will clear back up.
if, [00:14:30] you turn the pumps on though. While you dump that five gallon bucket and you're going to have the water is going to be circulating just a little bit and that's enough to keep those really, really tiny particles lifted.
So when
we see
Dr. Jesse Reimink: when Chris Bull Heis is, you know, out in his yard and he comes back and he's covered in all this hard pan dust from his hacking around in the yard, he jumps in the hot tub, he's gonna get it all milky and dirty and Jenny's gonna yell at him and say, Chris, you should have showered off. 'cause now you've gotten our hot tub all cloudy.
What are you
Chris Bolhuis: One of [00:15:00] many reasons why Jenny yells at me.
Yep. It's Just added to the
list.
Absolutely. so, what was I saying? You interrupted me there. I feel like I was going somewhere with that. What was I
Dr. Jesse Reimink: Yeah, it was something really important, so important that we
Chris Bolhuis: I think it
Dr. Jesse Reimink: what it was.
right?
Chris Bolhuis: Oh, come on now. so when we look at a rock, shale, let's say, That's right in front of us, pick a piece up, take a little bite off, and it feels really chalky, which means, you know, it's not cemented together very well, and, and it's made up of [00:15:30] tiny dust sized pieces, and That's why you get that chalky consistency. That says to me right there, wow, this was a very, very calm, quiet, shallow marine setting that allowed these particles to settle out and
form rock
Dr. Jesse Reimink: That's
exactly right, Chris. So, you know, understanding this process allows us to tell the story that is in the rock record that is held in the rock record. And you mentioned the Grand Canyon audio book where we have this great image, that talks about the shifting shoreline because we see this in the Grand Canyon.
[00:16:00] There are other places that deposit this kind of clay material. There's just a few of them and they're important. Actually, for most of the northern part of the U. S. and a lot of Canada, because glaciers, particularly these continental scale glaciers, when they were scraping across basically Canadian Shield, that glacial scouring creates what's called glacial flour, which is a relief, it's, almost clay sized particles, basically clay sized, very fine grained stuff, as, as the glacier is like carrying rocks and making these striations where it's just [00:16:30] grinding it along the surface, so glaciers they don't sort sediment, but they create a lot of this flour, and then when the
Chris Bolhuis: Yeah. They pulverize the rock,
you know, the, they, the rock that it's carrying gets pulverized and the rock that it's going over gets pulverized. It's a lot like sanding with a, if you use like a really, really fine grain sandpaper on a block of wood, know, you keep on just sand it, sand it, sand it.
You get this flower kind of material of wood, that dust wood, right? That's rock flower.
Dr. Jesse Reimink: Chris, that [00:17:00] is a great analogy and a great word for it, this pulverizing of the rocks. You're actually, you're just pulverizing it and sanding them down over time. Think of two kilometers of ice above your head. That's a lot of pressure. That's a lot of scouring force going on. and that clay, so as the glacier retreats, you think of these glaciers as a conveyor belt bringing this glacial flower to the front, and as the glacier is melting, it usually forms a big lake.
At the front of the glacier and that lake is really calm water and we'll dump off a bunch of this glacial flower So some a lot of these clay [00:17:30] deposits will Have been formed by at least in part some of this glacial retreat these lakes formed during the glacial retreat there And so we'll get that clay sort of sediment built up in the till in amongst the till basically
Chris Bolhuis: When, you see this Jesse in a mountainous area where there's still active glaciation and you get this, this rock flower brought to these small lakes, these are to me, know this is my opinion, but I know I'm right. These are the most beautiful lakes in the world, right? I mean, you're
talking about the colors when the [00:18:00] sun comes out is amazing.
shades of turquoise and teal and bright green. It's, it's absolutely stunning. Again, it's because of this suspension of these fine grained material in the water. it plays with the way the sun's light as it enters the water, so, you know, when you're looking at like a green lake in a mountainous area,
that's because of glacial rock flower.
Dr. Jesse Reimink: and it's just so beautiful. And you think about that on a continental scale, uh, with continental glaciers. I mean, it's, [00:18:30] it'd be spectacular to have these huge lakes that are full of this rock flower. So, Chris, has that, have we covered the, the grain size aspect of it?
again, just to reiterate that, we were talking there about clay as a size definition. The smallest grain size that you can have, and it's still being quote unquote detrital, like a piece of a rock, a piece of a mineral that's a very, very thin rock. fine, very, very small. So you could have a clay sized piece of feldspar or quartz or, smectite or amphibolite.
You could have clay sized [00:19:00] particles of any mineral that you want, and it would still be clay particle size. if you get small, you don't really get smaller than clay. Basically, you get smaller than clay and it's basically bonds are broken and it's dissolved. Basically, the only thing smaller than clay is atoms that are dissolved in the
water.
That's, that's
Chris Bolhuis: Yeah, that's right. That's right.
Yeah.
So I think this is a good time. Let's transition to the other way that we talk about clay. And now we're talking about mineralogy here,
a little chemistry involved in this now.
Dr. Jesse Reimink: so the clays are, as you said before, a group of minerals. [00:19:30] They're part of the sheet silicates. They're related to the micas, but they're different. So basically in the sheet silicates, you have micas, the mica group, biotite, muscovite, all the ones we talked about, you mentioned at the outset, Chris, and then we have the clays.
And the clays, there's really four different groups, and they're kind of It depends on the grain structure is really how these things are broken apart, but there's a kaolinite group, a chlorite group, a smectite group, and an illite group, and those are all individual clay minerals as well, so kaolinite is a clay mineral, and then there's other clay like minerals [00:20:00] related to kaolinite, so
Chris Bolhuis: I want to interject Jesse. Cause I actually have a question. We recently came out with an episode The
25 rocks you need to
know, do you make your students? Do you have clay as a part of your mineral set?
Dr. Jesse Reimink: No, I use clay Only at a really, really basic level. I talk about it as this group of minerals, I don't get into kaolinite and chloride and smectite. So I say, here's why you need to know clay. The clay group of minerals is [00:20:30] often formed by the breakdown of feldspar.
Chemical breakdown of
feldspar forms clays, and clays are
Chris Bolhuis: that is such an important point. that's the takeaway that, break down, particularly like feldspars, plagioclase feldspars, potassium feldspars, when they break down, they will chemically weather into clay minerals. Now, we're talking about the Chemical version of that, the sheet silicates, but you know what, Jesse, the thing is.
Is that those clay minerals often happen to be clay sized [00:21:00] as well.
And, and so that
further
Dr. Jesse Reimink: part, right?
Chris Bolhuis: right?
Dr. Jesse Reimink: It, hey, muddies the water. Nice
Chris Bolhuis: yes. So yeah, so here's the deal, Jesse, is that clay, if you take a rock that is made up of shale, let's say, it's,
going to have a lot of clay minerals in it. that are also going to be clay sized.
Clay sized minerals don't have to be clay. Clay minerals are almost always going to be clay [00:21:30] sized, but the reverse of that is not true. Did I say that
Dr. Jesse Reimink: That's exactly. right. You could have very small pieces of quartz that are in a shale, quartz is not a clay mineral, but it is a very small piece of quartz in there. So that's exactly right. And Okay. we don't need to get into the weeds here. But the reason that these things are often small is because, you when you break down the, feldspar structure, you need to reform a different structure with that.
All the elements, all the constituent parts of that recipe. So silicon, oxygen, aluminum, potassium, sodium, all [00:22:00] those parts, they are very common in clays. And they're often found with this two to one structure, but the reason that clays
Chris Bolhuis: Hold on, what do you mean by that? Can you just explain that real quick? I mean, not,
Dr. Jesse Reimink: Yeah. So
Chris Bolhuis: but what do you mean two to one structure
Dr. Jesse Reimink: we refer to these as sheet silicates, which means that there's a sheet of silica tetrahedron. And if you go to the Camp Geo app, we have some beautiful images in our minerals chapter of what a silicon tetrahedron is and what a sheet silicate looks like.
But you basically have a layer of silicon tetrahedrons, and then you have a layer of [00:22:30] cations in between them. Or you have two layers of silicon tetrahedron and one layer of cation. So it's either two to one or one to one. that part's not important. We'll get into that a little bit more probably later when we talk about, the geology of, of potter's clay and things like that.
But basically some of these for the homeowner, for your average homeowner out there, when you think of clay as a problem around your house, it's because some of them can swell. And it's only a certain group. It's the smectite group, which is minerals like bentonite and montmorillonite. Those ones, when you [00:23:00] add water, They swell.
That two to one structure has some space in it that can swell up, and the swelling can crack your house foundation, and then the drying, swelling, drying, swelling, drying, right? it's a big problem out west, in particular. Chris, is it
a problem,
Chris Bolhuis: I'm just going
Dr. Jesse Reimink: have
Chris Bolhuis: out.
Dr. Jesse Reimink: right?
Chris Bolhuis: I'm going to go out on a limb. No, I'm going to come in hot here. clay. Is my nemesis. I am anti clay.
Okay. I, I, um, I am anti clay. I do. because it creates problems for a lot of people here in the [00:23:30] Midwest, it, well, so not, it was a problem at my old house.
It was a problem at my old house and it wasn't
Dr. Jesse Reimink: I remember that. You know what? I forgot about that. You guys had,
you guys had some serious water problems with
clay,
in the basement, right?
Chris Bolhuis: That's right. So it was, it was
constantly on my mind. And, um, so I have PTSD from this. Seriously. It is, you know, my battle with clay, was never ending. I mean, I had a [00:24:00] sump pump. I had two sump pumps in my, in my basement, in my old house.
And then I had two battery backup pumps. systems for This because if it fails, you're in a lot of trouble. I mean, and so my issue with clay, and I think a lot of Midwesterners here isn't so much with the, with the smectite and, and the swelling, it's more from. Water, because when you dig a hole in the ground you put your, your, uh, basement walls in either, cinder blocks, or you pour concrete walls, then you backfill it, [00:24:30] but you're backfilling it against clay, which creates a hydrostatic low pressure and water is constantly then seeping toward your home,
toward your
Dr. Jesse Reimink: This is a really, really important point. We're going to come back to why clay does this, Chris, but in the Midwest, where it's the groundwater is more wet. I mean, the ground is more wet. Basically, it's, there's a lot more rain. The clay will often be wet in the Midwest. So it'll see, That backfill will soak water out of the clay, basically, and then fill in around your, your foundation, which is really bad.
And then you have freeze thaw cycles and all that problem. In the West, [00:25:00] like in the Denver area or in the front ranges, you have a big problem because there are former asphalt deposits, bentonite and montmorillonite layers. And when it gets really dry and those things, it's mostly dry out there, right?
And when you build your house, it could be dry. You get a big rainstorm or a ton of snow and the snowmelt swells that clay layer and it basically is just a massive compactor around your foundation. It can crack your entire foundation and then you got water coming and then you have freeze thaw cycles, you have wet dry cycles, and so this can be a really, [00:25:30] really big problem if you have, like you said, those clay layers sitting somewhere
right near your
Chris Bolhuis: Yeah. So. Yeah,
Dr. Jesse Reimink: also,
Chris Bolhuis: I don't have any issues anymore. in my new house, because I'm on top of a hill now. I'm able to just get my water away from my house before it enters
my house. Um, it's very
easy for me to like, I, got this all figured out.
but. if you're not in my situation, where I was at my old house, it was just a, it was a, constant battle. I mean, every
time that we [00:26:00] had events, it was always on my mind and I'm glad
to be away from it. So
Dr. Jesse Reimink: absolutely. so Chris, one point about this, this phenomenon we're talking about is, and I think this, this might be apparent, is that in order to form clay, there's a lot of water in clay, at the outset, but clays are really common on the surface of the earth.
They're extremely rare. Uh, deep in the earth or in the solar system. Because they require, you talked about this process, breaking down feldspar to form [00:26:30] clay minerals, that requires low temperature water and a lot of different oxidation states have to have an atmosphere and water and low temperatures and feldspar on the surface.
And that combination is only on earth. And, that clay composition has changed over time on earth, but we've had clays for quite a long time.
Chris Bolhuis: that makes me think what you just said, that makes me think of why Michigan has so much, you know, residual clay. This isn't shale. This
wasn't deposited. So two kinds of clay that we [00:27:00] talk about often. One is a clay that forms in place. And that's what we deal with a lot in Michigan.
And the other one is a transported clay. In other words, it was
feldspar that got broken down.
Dr. Jesse Reimink: I want to clarify this, cause I don't think, this is a ho
Chris Bolhuis: I'm going to come back to it a second.
I'm going to come back. I'm, So the other one is a transported shale where you have feldspars and other silicate minerals. They get chemically broken down by warm surface waters and then carried to a lake or carried to an ocean basin.
And they'll [00:27:30] eventually deposit out in very calm, quiet waters and form the rock shale. That's a transported shale. back to the residual shale that we have. we have all this glacial kitty litter that covers Michigan, 200 to 500 feet of rock that came from basically the Canadian shield during the last ice age.
the last 15, 000 years, the Canadian shield is loaded with granite, which means it has a lot of feldspar. So this stuff just got plopped off by the ice. And then over the last 15, 000 [00:28:00] years has chemically weathered into clay that's in place. And that's why we call it residual.
Dr. Jesse Reimink: this residual phenomena, I find that students have a, this is kind of a hard one for people to understand this difference. I think an easier explanation or an easier setting to imagine residual clay is if you're in up in New Hampshire or Vermont or Maine, where you're sitting right on top of granite and there's soil above the granite, If there's clay in that soil, that's residual clay, because the clay, actually, the clay mineral was [00:28:30] formed right on top of the granite.
What you're referring to in Michigan is there's a feldspar grain in the soil, or a granite piece in the soil, and that, in Michigan, in the soil, in the last 10, 000 years has broken down into clay. that's the residual part there. it's where the clay mineral itself formed, not this like intermediate soil transport by the glacier.
So, anyway, Chris, a question for you. which one do you think is more important? or do you emphasize one
Chris Bolhuis: Oh, oh, okay. Um, [00:29:00] can I ask a question before I answer it? when you say important, what do you mean? In what context?
Dr. Jesse Reimink: I guess. well, whichever one you want, I guess. I
mean, you know,
which one do you focus on in class, I guess, is
Chris Bolhuis: Okay.
I 100 percent will focus more on the clay that you find in the rock shale.
And reason for that is because shale is the most common detrital or clastic sedimentary rock on the [00:29:30] surface of the earth. it's not the most common sedimentary rock, but it's the most common clastic one.
And there's a reason for it. The most common mineral in the, at the surface of the earth is, is feldspar. And feldspar very easily chemically weathers into clay. Minerals, Okay. which get taken out and deposited in lakes and ocean basins. So because feldspar so abundant and what happens to feldspar, that means that shale is going to be it's an [00:30:00] abundant rock at the surface of the earth.
Dr. Jesse Reimink: Yeah. Okay. I think that sounds right uh, from an intro to geology standpoint. I think there probably could be an argument that, like, your, your average everyday life, these residual clays are so common, they form very readily that, you know, if you're a homeowner digging around in your yard, you're probably hitting residual clays in some way, shape or form.
So, I think you're totally right. That the understanding of how shale forms is way more fundamental and way more
important from like a global scale.
Chris Bolhuis: But from a homeowner's [00:30:30] perspective and standpoint, residual clay is far, far more important. And so probably to the everyday layperson, residual clay is more important. if you're going to build a house and you have two possibilities for building two lots, one is in sand and one is in clay, building sand every day of the week and twice on
Dr. Jesse Reimink: Absolutely. Yeah. Yeah, totally. Totally. Right. Yeah. Oh my goodness. Yeah.
Chris Bolhuis: Yeah. Jesse. So, I mean, back to the whole shale versus residual clay thing. Uh, [00:31:00] have this thing, that I bring a bunch of shale up. to the front of my room. I put it on a cart and I'm like, okay, let's have everybody come up.
Everybody get up. Okay. Walk up here, grab yourself a little piece of shale. And so they all do. I'm like, oh, okay. Go back and sit down. I pick up my piece of shale and I'm like, so how do you know? If you have shale in your hand, is this a silt stone? Is it shale? Is it sandstone?
Is it something else? Well, shale has a couple of properties that are pretty easy to discern in the [00:31:30] field. One is it's a weak, soft, crumbly rock. It's not lithified in a typical way where it's cemented together. It's only compacted. And so you can easily bite off a little corner of shale with your teeth without, doing any damage.
So there's one. The other thing is, is that shale is very, very, well, it's made up of clay size pieces, right? Tiny, tiny pieces. Then you see, you don't get a lot of grit, so you can easily bite it [00:32:00] off. And when you do, it turns to this chalky sort of consistency. So I say to everybody. Take a piece go ahead and bite it chew it and and so we have shale communion in my
Dr. Jesse Reimink: I mean, so good. And is this one of these where you get a bunch of high fives as they're going out the door because they had a bite of shale? Or do you get a little bit more, You'll never believe what Mr. Bolhuis made me do!
Chris Bolhuis: Little bit of that a Little bit of that but you know you [00:32:30] always it's funny, too You get the personalities of them coming out too because some of the kids will try to take They'll go for like a they're like they're biting a potato chip, you know, they'll bite it right in the
middle of the rock
Come on just a
Dr. Jesse Reimink: Come on. Yeah. Little nibbles all you need. That's exactly right. I mean, on that note, Chris, those of you out there who researching an area or reading, descriptions of rocks, the term argillaceous comes from Adding clay. So if you have an argillaceous limestone, the limestone, it's mostly limestone, it's mostly calcite, [00:33:00] but there will be some clay sized particles into it.
So that like a modifier or an argillaceous sandstone means that there's some clay pieces in there because it's rare that we have just pure end member shale or sandstone or limestone there's, there's often, you know, blends of them. So
that's just a a random
Chris Bolhuis: I'm sit, I'm sitting over here shaking. Hold on. I'm under your argillaceous. I'm sitting over here thinking of one thing, here. You said argillaceous. And I think of another really dumb name that we have in geology, which [00:33:30] is a burial metamorphosed shale will turn into argillite. know,
it's, it's a common rock in Glacier National Park.
It's beautiful, but
again, it speaks to your point earlier of, where do we come up with these names? And why do, why, why don't we just call that slate? Why do we differentiate it and call it argillite? And it has to do with the, it
forms differently. It's not a regionally metamorphosed
rock. So
Dr. Jesse Reimink: I was, uh, I was reading a bunch of older literature on, the sedimentary [00:34:00] record and actually the old term for shale used to be luteite or luteite, L U T I T E.
It's mean, so these words, uh, eighties, seventies or eighties, And so it's like, you know, not only are the names dumb, or are they hard to remember, they're just one off names, there's no systematic, but they've changed over time.
I mean, the geology naming team is crazy, but hey, we're in it, so, and it's kind of fun to learn All these one off words, so. Um, one other, Note about clays, Chris, that I think is interesting, and it [00:34:30] may be a good one to end on, is that there have been suggestions, and this is, this gets into territory where we have really no idea how life formed, but clays have been suggested as a possible source of life because of this, two to one structure, or this one to one structure, we have a silicate layer, a silicate tetrahedral layer, which is really well held together, and then cations in between that are kind of loosely held, and you can fit water in there.
we know that these clay minerals can also, they can help assemble RNA molecules. And there is actually a proposal that [00:35:00] the first actually self replicating organisms were iron rich clay minerals that fixed carbon dioxide and kind of replicated themselves. So, I mean, this originalized stuff is wild.
I can't claim to understand a lot of it, but that's an interesting, mineralogical phenomenon there.
Chris Bolhuis: Yeah.
That's, crazy stuff right there. How new is this? Is this
Dr. Jesse Reimink: uh, this is going back to the nineties, nineties, early two thousands, these, types of proposals. And there's a lot of, I mean, just type in origin of life and there's all sorts of proposals for how this [00:35:30] stuff formed. but a lot of it comes down to mineralogy, these mineral water interactions that have a lot of chemical potential energy to sort of start this process, kind of kickstart the process.
Clay is one of them. So, Maybe an interesting way to end on, the clay as a mineral, the group, the clay group of minerals.
Chris Bolhuis: And also in geoscience, we just need to do a better job of, all right, what kind of clay are we talking about here? We talking about
particle size? Are we talking about mineralogy? We could do better. I could do better. I certainly know [00:36:00] that.
Dr. Jesse Reimink: Yeah. I think that's right. Almost yearly that I get called out by a student for You know, mixing, as you said at the outset for mixing up the words or using them in multiple different ways in the same lecture. So, Hey, that's a wrap. Thanks for listening to Planet Geo.
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Chris Bolhuis: Cheers.
Dr. Jesse Reimink: Peace. [00:37:00]
