GeoGems: rocks

Hi, welcome to another exciting episode of our new series called GeoJemps and in GeoJemps we take you back to some of the foundational important topics for someone who just curious about Earth and GeoSans in general, so today we talk about rocks, why do they come in so many flavors, we're going to take you through the different kinds of rocks and the rock cycle, whenever I tell someone that I'm a geologist the first thing I get asked is why do I study rocks, I always get go, because people overlook the importance of rocks, but do you know that rocks can help us understand how the earth has changed over time, studying rocks can help us understand the geological history of an area and also help us understand even how earthquakes or global warming might affect the earth in the future, so we want to start today by defining what a rock is, talking about the rock cycle and the fact that our planet runs on cycles of which the rock cycle is one, we all learned about the hydrologic cycle but maybe we're less familiar with the rock cycle, we tend to think about rocks as unchanging things and associate them with permanence, but the reality is that no rock is safe from transformation, it's just that it happens on a time scale that's usually much longer than our planet, so Eliika, you want to take us into the three main categories or classes of rocks? Perfect Kyron, again, welcome everyone, so before I even talk about the three main category of rocks, just for those of us who may not be familiar with what a rock is, when we think of rocks in plain language, what we want to think of is the fact that a rock is naturally occurring solid mass or aggregate minerals or mineraloid matter, and so these are essentially the building blocks of the earth, the less geogin that we did we talked about minerals, so we want to appreciate that once these minerals typically come fragmented, they contribute to the building block of the earth's solid outer layer and interior, and therefore rocks can be categorized by mineral composition, chemical makeup, and how the rocks themselves are formed. With that being said, it's important to think about the fact that we typically divide rocks into three major groups, and those are our igneous groups, our metamorphic groups, and our sedimentary groups. What does this mean, why are we using those big words, how do we divide them? So essentially our igneous rocks, those are our rocks that tend to form underground or intrusive or above ground, and that makes them extrusive, and they're associated with lava or magma, and when you think of a volcano erupting, you think of that molten hot stuff, you want to appreciate that it's classified as lava, magma, depending on where it's located, and we'll take you through that in another episode. So for now, just appreciate that igneous rocks are a result from either magma underground or above ground from lava. Then our second group of rocks or rock type will be our sedimentary rocks. Our sedimentary rocks are the rocks that are formed near the surface at low temperatures from bits of other rocks and minerals or precipitate from water. Our third rock type, those are our metamorphic rocks, and those are the rocks that form from the application of heat and pressure. But the heat and the pressure is not enough or intensive enough to melt them. Otherwise, guess what, you're back to your igneous rock, and that's why it's called a rock cycle. Karen, so we've talked about what rocks are, the different types of rocks. Do you want to give us a little bit about how we classify the rocks? Yeah. Sure. So just before we jump into that, I know Elmo has a pet peeve against pet rocks, but do you have a favorite category, Elmo? I really did break my heart that Elmo is not a fan of rocks, but I understand why that particular rock kind of ticks them off because I agree. But I will say, honestly, I'm an igneous girl. What's your favorite rock type? You know, I affectionately refer to them as the trash rocks of the rock who, but sedimentary, those are my absolute favorites. I'm getting some main character energies. I mean, they are kind of trashy, right? You take a bunch of stuff, you don't tend together, you can compact them or cement them, glue them together, and voila, new rock. It's just recycled stuff. And I guess that's a beauty of the rock cycle. Everything is always being transformed or recycled into something else. You ever saw that episode of the office? Did you watch the office? I was not an avid watcher of the office, but I did see a couple episodes and no, I think I may have missed. Were they talking about rocks? Oh, it was actually like, by true assistant, the original manager was in charge of like office safety, right? And basically, with him as the office safety person, liaison, no one in the office was safe, because he conducted a very unsafe fire drill. But I imagine that's a rock's view. From the time that they get made, they always have risks. They're not safe. They're always being broken down, acted on by forces and transformed into other things. So, we classify rocks based on their origin, igneous rocks, those made from fire, basically, like ignite, igneous fire. So think magma or lava, sedimentary, made from bits and pieces, and we classify them based on the size of the particles that are in them. Metamorphic rocks, heat and pressure, not enough heat to melt, and we classify them largely based on the degree of metamorphism, how intense that heat on pressure was, and whether they have liering or fully Asian. So that kind gives you a big picture overview, but we want to give you a little more, how to recognize and understand what you see in a rock, to be able to classify and characterize it. So for sedimentary rocks, you want to look for class. Think of these as bits and pieces, broken, weathered, wonderl, bits of rock, fossils or minerals that are held together, bone together to make a rock. What about metamorphic rocks? You want to tackle that one? No, no, no, no, no. I'll do metamorphic since you love igneous, alright, I'll leave that one for you. So for metamorphic rocks, you want to look for banding or fully Asian. Think of these as layers, right? And depending on the degree of metamorphism, you will see layers that are segregated, like light dark, light dark, light dark, these layers often are folded or bent. You can really see that they've been subjected to lots and lots of pressure. So in the degree of metamorphism, if it's just a little bit of heat and pressure, you will see that layering, but it's like a sleep. And as that pressure and temperature ramps up, those minerals actually start to look more crystal like you start seeing shinier surfaces, shinier minerals, and at the very top end of the scale, like really high in metamorphism, like a nice rock, it's G-N-E-I-S-S, pronounced nice, that's like where we start seeing those minerals separate. There's another subcategory of metamorphic rocks that don't have that layering or fully Asian and a good example of that is marble. And interestingly, every metamorphic rock, none of them are original. They have to start as another rock, so we need like a pair and rock that we have to then heat and pressurize to create a new metamorphic rock. So marble, it's parent or original rock is limestone, my absolute favorite. Apply heat and pressure, voila, you have marble. So the floor is yours for igneous rocks. Thanks Karin. And so a couple of fun facts before I even go into the igneous rocks. Yes, I did actually see that very care like episode of the office with Dwight and that fire trail, actually one of my favorites and a classic, secondly, for those of you all who don't know, I am an interdisciplinary geoscientist. And part of my practice is I am a set of entologists. So it's kind of ironic that my favorite rock group belongs to the igneous rock type or grouping. So I just thought I'd share that little fun fact because I was thinking about it and when you just commented that you would leave my favorite rock for me. But with that being said, getting back on track, sorry to digress, I do that a little bit. Ah, classification of rock type igneous, those igneous rocks, which you talked about being formed from the cooling and solidification of magmaral lava, essentially results in different properties being established. And these properties that help us identify igneous rocks depend on their composition and their cooling conditions. So what that means is that if you have your igneous rock forming underground with cooling slowly and solidifying from the molten rock called magma. What you would see is that you would see these beautiful or you would see a range of developed crystals for your rocks that cool more rapidly above the surface, your extrusive rocks, what they will do or what you would tend to see happening with those rocks is that you would see a more glassy appearance. So if your rocks are slowly cooling below the surface and they have those crystalline appearances, those would be like your granites, your granites, your diorites, your gap rooms, those will be your intrusive rocks formed from magma. Those that are on the surface that are rapidly cooled, your extrusive rocks, those formed from the lava, those would be your rye light, your anticides, your basalts. So they would be glassy in appearance, you wouldn't really see any detailed crystals like you would with your intrusive rocks. So the more time the crystals have to develop, the more that you can see them in appearance, those let you know that they're intrusive. The less time the glassy or appearance, those will be extrusive. So think about like when a volcano erupts and a material ejects and you're getting those basalts and those bombs, those are a great example of your extrusive rocks. So that's kind of one thing to know about them. Also with your igneous rocks, another property that you can look for are your colors. So your igneous rocks could be light colored, meaning that they're felsic or they could be dark colored, which is they're a mafic in nature. So your felsic rocks are actually rich, typically rich in silica and elements like sodium and potassium. While your mafic rocks, those are rich in your irons and your magnasiums. So that's like some of the cool things about rock properties. Is that rock properties really help you to identify the type of environment that the rock was created in? Whether there's sedimentary, metamorphic or igneous in nature, because identifying your rocks or your rock types are really important. They help you to start developing analysis on interpretations. Yeah, definitely. It's important to understand what kind of rock you have, because a rock is basically a glimpse into what the environment or what the conditions were like at the time that a rock was being formed. I think the most appreciable example of this is with igneous extrusive rocks like that mafic visis felsic, light visis dark, like the kinds of rocks that you find around a volcano can give you a lot of insight into just how hazardous that volcano might be. So those dark colored rocks tend to be produced in more gentle eruptions, but if you find a volcano that has lots of light colored rocks around it, that is one that is going to be particularly hazardous. And of course, rocks are great resources. We have lots of things from them. So understanding what kind of rocks you have in an environment tells you where economic potential might be. And I think for studying the history of our planet, interpreting the future of our planet, and extracting resources that we can use here, I know, makes rock classification and understanding rock analysis really, really important. So true. So yeah, next time you think of our rocks, remember that it's more than just rocks for jocks. They are the building blocks of our earth. They are important, and they tell us a lot about our history. But again, that's all for today folks. We look forward to continuing to exploring earth's materials and processes with you all by this series. So if you enjoyed today's conversation, get in touch with us. Do you have any questions about geoscience, or maybe why some natural disasters seem to be occurring more commonly, or perhaps you're just curious about how the physical world works? Send us your questions and we'll do our best on the answers you seek. To this ad geotrip podcast, or email us at [email protected]. And don't forget, geoscience is everywhere around us. So next time you're outside, take a look at the rocks, the mountains, or even the ground beneath your feet. There's a whole story written in stone just waiting to be unraveled. See you on the next episode of the geotrip.