How Are Rocks Formed?
36:02 Share

It's fall and many kids are headed back to school and they're on the hunt for the perfect book to read. Don't forget to check out our But Why book series. We have two books perfect for young readers about age 8 to 10. Look for Our Llamas Ticklish and Do Fish Breathe Underwater wherever you buy your books. And if you prefer to listen to books, check out the audiobook versions as well. You can find out more at butwhykids.org books.

But why is supported by Progressive, where drivers who save by switching save nearly $750 on average? Quote now at Progressive.com. Progressive Casualty Insurance Company and affiliates national average 12-month savings of $744 by new customers surveyed who saved with Progressive between June 2022 and May 2023. Potential savings may vary. ♪♪

This is But Why, a podcast for curious kids from Vermont Public Radio. I'm Jane Lindholm. On this show, we take questions from curious kids just like you, and we find answers. Hold on to your seats because today things are going to get rocky.

That's right. We're answering questions about rocks. Hi, my name is Catherine and I'm eight years old and I live in Omaha, Nebraska. And my question is, how are rocks made? Hi, my name is Tyson. I live in Greenwich, Connecticut. And my question is, how do rocks form?

this is Olive. I am seven years old. I live in Tacoma, Washington and my question is where do rocks come from? We found someone very cool to help us out. My name is

Dr. Hendrata Ali. Hendrata is not a medical doctor. She's a rock doctor. She studies rocks and teaches at Fort Hayes State University in Kansas. She's a geologist. A geologist is someone who studies the solids, liquids, and gases that make up the Earth, sometimes other planets as well. Hendrata Ali just studies Earth, though. And she says there's another title she goes by as well.

Yeah, I'm an earth scientist. That's what they call me because I look at everything that affects our life on earth.

And she was thrilled to hear some of the great questions you've sent. I want to warn you before we get started, though. This episode is just a little bit longer than normal. So you might want to listen until we take a break about halfway through. Then you can take a break, too. Spend a few minutes zooming around your yard or your room or apartment or classroom. Get the wiggles out and then come back for the second half.

Okay, let's get right to it. My name is Harlan. I live in Aspen, Colorado, and I'm five. My question is, what are rocks made of? Hi, my name is Wyeth, and I live in Renath in Pennsylvania, and I'm seven. And my question is, what are rocks made of? What are rocks? Rocks?

are the hard part of our earth if you think about it. The really solid hard part of our earth are rocks. They are generally very very large but usually what we see are the tiny bits that have been plucked from them. Broken, shaped and moved around. But if you took off

All the trees and the dirt and the waters, what you would see would be an endless stretch of rocks that just covers all our earth. But if you were peeling back the grass and trees and soil to see all that rock, it wouldn't necessarily all look the same. The earth is covered by different types of rocks, and the rocks on earth can move around.

Rocks move and change because of other things that are on Earth, because of our environment, our climate, water, the weather, heat, cold. These are the things that would transform rocks from one type to another and give it the character that it gets where it is at any given time. My name is Booker. I am six years old. I live in Manhattan, Montana. I want to know how were rocks formed.

Hi, my name is Vivian and I am six years old and I live in Pullman, Washington. And my question is, how are rocks made? My name is Emily. I'm seven years old. I live in Atlanta, Georgia. And my question is, how do rocks form?

I am Myosh and I live in Evergreen, Colorado. I'm five years old and my question is how do rocks get made? How are rocks made? How are they formed? This is a most important question. Thank you all for asking. To know how rocks are made, maybe I have to tell you about the things that make these rocks, you know. So in a way,

I want to talk about where and how rocks start their lives. If you think of them as having lives, then we talk about them starting their lives just like babies. Although they aren't alive, just to be clear. They're not alive, yes. They're not alive. Okay, we've established that rocks are not alive.

However, they do have different stages. And Andrada says it's kind of easier to understand if you think about it a little bit like a life with different stages, like baby, child, older adult stages.

And I hope you're not listening to this while you wait for breakfast or lunch or dinner or something, because the way Hendrata Ali describes the early stages of the three main types of rocks, well, it just might make you a little hungry. Like, take this first group of rocks. The first rock starts their lives like very hot, runny, yummy, creamy soup. The soup is called magma.

It makes me want to eat. Okay, we'll deal with that later. Yeah, you do not want to put magma in your mouth though. No, don't do that. It is hot, but we'll call it the runny yummy rock soup. Okay, let's just call it the runny yummy rock soup. The second rocks start their lives in a different way, like tiny weeny candy bits. Don't eat rocks.

But we call them sediments. Like we're scientists, so we call them sediments. I would call them tiny, weeny rock beads because I just like it, right? And then the third type of rocks, they start as stretchy, bendy play dough called protholite. So we just call them stretchy, bendy rock dough.

There. So those are the three ways that rocks start their lives. Okay, so that's how the three main types of rocks start their development. We're going to learn more about each of these rock types, starting with the one Hendrata describes as soupy. These rocks are made from magma. That's the hot, runny stuff she was talking about. The rocks that come from magma, once they have hardened, are called igneous rocks.

Let's learn more about them, starting with that soupy stage. The soup is really, really very hot and it comes from deep inside the earth through a volcano, right? It comes through a volcano. When the rock soup comes to the surface, it starts to cool because it is not as hot on the surface as it is deep, deep, deep inside the earth. It becomes cool and it becomes thicker and

and it is not so runny anymore. It will cool into a rock. These are volcanic rocks. They can be different colors and can actually develop bright, shiny crystals inside some of them. Again, all rocks made from magma are called igneous rocks, and they're often formed deep inside the Earth. Although sometimes volcanoes will erupt above Earth's surface and create new volcanic rocks right on top of the Earth.

The second group of rocks is made up of little rock bits. These are called sedimentary rocks. So sedimentary rocks are made up of sand and dirt and sometimes leaves and plants and even animals that get pushed together and over time with a lot of pressure turn into rocks. You'll sometimes find shells of ancient animals inside sedimentary rocks.

Here's how Hendrada describes them. Teeny weeny rock bits, tiny, sometimes not so tiny though, but they're smaller than the big giant rocks. These rocks are called, these particles or these bits from which the rocks form are called sediments because they are loose, right? You can pick them up, you can throw them around. They are just tiny little baby rocks,

that are smaller than the big rocks. When these baby rocks gather in a large pile, sometimes these piles are in a lake, a river or even the ocean and they pack and other tiny bits of rocks or particles or sediments begin to fall on them. They get buried. They get buried and they go deeper and deeper and deeper inside the earth

And suddenly the weight of the other particles that are sitting on them begin to squash them and they become packed closer and closer together. And because they are in water, the water also has air.

glue that we call cement and as this bits of particles get packed and glued together they begin to form rocks that we call sedimentary rocks.

The force that's pushing all of those rock pieces together, along with the water, which acts like a glue or cement, is what binds those little rock pieces together into a new, much bigger sedimentary rock. The interesting thing, though, is that sometimes the glue is soft, just like paper glue, and so the rocks are not bind so hard.

Sometimes the glue is really tough, like super glue, and the rocks are stuck together, the sediment are stuck together, and the rock is really hard. It just depends on what Mother Nature really wants to throw at us. Okay, so now we know about igneous rocks and sedimentary rocks. The third main family of rocks is called metamorphic rock.

And that's what Hendrata calls stretchy, bendy rock dough when it's in its early stages. And you know that when dough is cooked, it becomes something different, bread or a cookie or something like that. But different from when it was just dough, right? Well, that's key to metamorphic rocks. This rock is a whole rock that does not break into particles, but it is morphed.

right like a dough into something different which is a new rock so you have an old rock that we call the protolith that is heated because of the hot temperatures that are deep deep underground it makes the rough a little bit soft and because of all the pressure that is on the rock the rock can be stretched

It can be bent. It can be squashed. It's kind of morphed into a new rock that we call a metamorphic rock. So this is the stretchy, bendy rock because it does not really melt into a magma. It does not break apart into particles. It just, as a big giant rock, gets transformed into another rock because of temperature, high temperatures and heat.

And it's interesting because I think metamorphic, if you go back and look at the history of that word, it means change, right? So the whole idea of this rock is that it's been changed, morphed, reshaped and changed over the course of its life, as you call it. Yes, it's been morphed from an old rock into a new rock. What a transformation, right? Now I want to go see a metamorphic rock. Yes.

Well, good. I'm glad you said that because we also got a question from Olivia, who's nine. Olivia lives in Virginia. My question is, how did the rocks in my backyard originally form? Now, Hendrada, I don't think you know exactly what rocks are in Olivia's backyard. But if we wanted to find out what kind of rocks we have in our landscape around us and how they were formed, how could we figure that out? There are so many clues that

geologists would use to figure out how the rock in your backyard formed. First, you look at the rock. You just look at it to see if it is made up of so many different types of minerals or bits and pieces. Then you look at if you can tell what types of minerals those are and how they are arranged in the rock. That is a big clue. We talk about texture.

just like texture of a fabric, how it looks, how they are arranged and what color they have. Some rocks like igneous rocks crystallize, they form crystals and you can see beautiful crystals that are tightly packed together. Sedimentary rocks because they are formed from beads that are put together

Sometimes they have tiny little bitty holes in them that we call pores. And so often if you even drop a bit of water on that rock, sometimes it might soak the water because of these tiny little bits of holes that are in them. So you would know that maybe this is a sedimentary rock.

Metamorphic rocks, like I said, sometimes they are stretchy, bendy. So look at the minerals or the particles in the rock. Sometimes they are stretched. They are stretched in one direction or another or they are just squashed into one big blob. So there are some clues that we look at. So I don't know what rocks are in her backyard.

But also, if you just look at the history, sometimes you can just look at the history of a place and say this place, because it was a lot of water and sedimentary rocks mostly formed in water, chances are the rocks in this area are sedimentary rocks. So sometimes you can also have a best guess like that.

Hi, my name is Lukey, and I'm six years old. I live in Wellesley, Massachusetts, and my question is, how do big rocks get created? Maybe we could talk a little bit about why some rocks are bigger than others, or, you know, are all rocks just...

pieces that have fallen off of bigger rocks? You know, is there a difference between a big rock and a small rock? So what we get, what we usually call rocks, when I say I have a rock, really what I'm saying is I have a piece of a rock, what we call a rock sample, right? It's a piece that has been taken from a bigger rock. Because the rocks are so big and large, we cannot really move them because that's what we are sitting on.

So we cannot move these big giant pieces of rocks. We have to take samples. Sometimes we

break bigger pieces sometimes we break tiny pieces so it depends on the piece that is broken from that rocks sometimes it is not us sometimes it's nature that breaks these pieces of rocks as well right they may fall off a cliff they may be broken by wind water or maybe they scratch against each other so it really it's really an interesting way to look at rocks

So I guess, Lukey, the big rocks got created the way Handrada was telling us earlier, through those natural processes, like for sedimentary rocks, lots of small particles being pushed down on and glued together by the pressure and water. And then smaller rocks are just chunks of bigger rocks. In just a minute, are all rocks hard? No! Some rocks are so soft you can draw with them. Take a couple minutes for a wiggle break and then come right back. ♪

This is But Why, a podcast for curious kids. I'm Jane Lindholm, and today we're learning all about rocks with geologist and professor Hendrata Ali. We've been talking about how rocks are formed, and we learned that there are three main types of rocks. But within those three types or families, there are so many different kinds and so many different ways they can look.

I asked Hendrata to explain a little bit about how rocks can be so many different colors. Rocks get their colors from the material that makes up the rock. And this material is called mineral, right? Minerals have different colors. They have different forms. They have different structures. So minerals are really the sacred of rocks, right?

because all rocks are made of minerals and one single rock can be made of so many different minerals and the different minerals together then gives the rock its texture and its appearance of the color that we see.

Hi, my name is Ray. I'm five years old. I live in Brooklyn, New York, and I want to know how do rocks get hard? Rocks are hard because of the minerals that are in them. So when you hold a rock and you can throw it, don't hit anybody, please, and you can play with it, that's because it is hard, right? You can feel it.

The hardness depends on a few things. Let me list them for you. The first is the type of mineral that is in the rock. So every mineral has a hardness. It's actually...

organized on a scale, what we call a Moh scale, right? From the hardest mineral that is diamond to the softest mineral that is talc. If you have been a baby and all of us have been babies, we probably have talc on our bottoms, right? Yes, we think of it as talcum powder, baby powder. That's just talc. Baby powder, that is just talc because it is the softest mineral. It's so soft, we want to put it on our bodies and feel good.

That is a soft mineral. Then the hardest mineral is diamond.

So diamond can crush almost any other mineral, right? We cannot easily crush diamond. In fact, diamonds are used in a lot of tools. People think of diamonds in jewelry and fancy things, but diamonds are sometimes used in tools because they are so hard. Because they're so hard. Want to know more about diamonds? Rosie does. Rosie is six and lives in Providence, Rhode Island. And my question is, how are diamonds formed?

Diamonds are formed deep in the earth where there is heat and high pressure. This can be as deep as 100 to 150 miles inside the earth. Most of the diamonds in the world are formed in special rocks called kimberlites that form from magma. The heat and pressure in the magma cause the carbon inside the magma to crystallize, that means to grow crystals, and make diamonds.

Diamonds are not really rocks. They're minerals that are formed from just one element: carbon. Diamonds are pretty interesting and precious. As Hendrata said, they are the hardest naturally occurring mineral on Earth. They are also all very, very old. Every naturally occurring diamond on Earth is more than a billion years old. Some are more than three billion years old.

But if diamonds were formed so long ago and so deep below the Earth's surface, how do we get them today? No one is digging 150 miles into the Earth to get them out. These diamonds have mostly been brought up closer to the Earth's surface over the ages by volcanic explosions. Which brings us to something else neat about diamonds.

You know how we've been talking about the different kinds of rocks, igneous, metamorphic, and sedimentary? Sometimes you can find examples of all three of those processes in the same rock area. Diamonds, as I said, are metamorphic minerals. They were made when carbon was put under extreme pressure and heat. And these diamond crystals formed mostly within vertical tubes of igneous rock.

And those igneous rock tubes are often found in larger sedimentary rocks. Pretty cool, huh? One more thing on what might make a rock hard or soft beyond just the individual minerals that are kind of like the ingredients of the rock. The second thing that can make a rock hard or soft is

are the amount of tiny bitty holes or spaces that are found in the rocks. Sometimes they are really tiny. We cannot see them with our eyes, but they are there. Like I said, one way you can test that is to drop a little bit of water on a piece of rock and see if it soaks the water. If that rock soaks the water, it says that it has pores. It has tiny spaces in it.

So if a rock has a lot of pore spaces, it will be softer than a rock that does not have a lot of pore spaces. Here's a question from Kaya that has to do with hardness and softness too. Kaya lives in West Lynn, Oregon and is 10 years old. Why can you draw with rocks? Why can you draw with some rocks? Ooh!

Why can you draw with some rocks? That all has to do with the hardness of the minerals that are in the rock. So let me say this again. The things that make rocks soft, because we can only draw with rocks that are really soft and sleek.

which means that they are soft but the minerals in those rocks are also smooth and shiny so that when we draw with them we can actually see right so the softness of the rock and that depends on the minerals that make up the rock so for example say talc maybe calcite whether the minerals are slippery and smooth so that when you pull it on the surface it can leave a mark

And also whether the mineral has a color that you can distinguish from what you're drawing on. So if a rock has all of these three properties, then you can draw with it. And an example is chalk, right? You know about the chalk that we use in school. But there's a rock that is called chalk.

It's made of a soft mineral that we call calcite. But these are really so tiny, tiny microorganisms that died a long time ago. And you can draw with it. But another mineral that we don't even think about, that we draw with it every day, that is, it is soft, it is slippery, it is smooth, is graphite.

If you've had a pencil, you've probably used the mineral to draw. It is dark. The color is really dark and black. So when you write on a white sheet of paper, you can see it because it's shiny. So yeah, that's my favorite mineral because I use it every day. So we are writing with rocks every day. You're writing with minerals.

Rocks with minerals. The mineral is graphite and the graphite can make a rock. Actually, graphite is really interesting because the same substance that makes up graphite is the same substance that makes up diamond. Can you imagine you can go from graphite and become as hard as diamond?

My name is Sahara, and I'm five years old, and I live in Nairobi, Kenya. And my question is, how do rocks shine? Sahara wants to know something that you were kind of just talking about with graphite.

Why are some rocks shiny and how do they shine? This is the most fascinating question I have ever had, Sahara. This question makes me think. So rocks shine because of the way minerals reflect light. I use the word reflect. It's a big word, but really what I'm trying to say is just the way light bounces off of a surface and gets into our eyes so we can see.

So, some surfaces and some minerals, they are so smooth and sleek that they bounce the light off in a very uniform way, in a smooth way. And that makes us see things as shiny. Like the mirror. And then some things, the surface is not very smooth, even though it may look smooth, but it's a little bit rough if you really look close. So they bounce the light in a scattered manner.

And that doesn't give us the shine. While we're talking about shiny things, we have a couple of questions about shiny rocks, other shiny rocks. Hi, my name is Esther. I live in Arlington, Massachusetts. I'm six years old. And my question is, how are rocks made? Oh, how are geodes made?

How are geodes and crystals made? Ooh, I call geodes the O-Rocks. The O-Rocks? Yes. Geodes are rocks that often look like O's, right? Because they're enclosed. So they're the O-Rocks. And they often have crystals in them. So they are really exciting. I like geodes. If you take an O-Geode and you break it, you may see crystals.

The crystals are made because, remember I said sometimes rocks have really tiny bitty holes on them? So when they geode the old rock that has this cavity inside, has tiny holes in them, water soaks into the geode and this water brings with it chemicals.

that start to grow as crystals. It takes a really long time because the critters take their time because they want to be beautiful. They really do take their time. They grow slowly and over time as more water seeps and soaks into the oil, the crystals grow and grow and someday they are big enough that if we take it and we break it, then we see the crystals. So the older the geode, the larger the crystals because

Because it's hard time to form nice and long. And they're usually very beautiful colored minerals. So it's not just one kind of mineral that is in a geode, right? You get several different colors, several different crystal forms because so many different minerals can get in through with that water.

I spent a lot of my childhood using a hammer to break every round rock that I found in the hopes that I would find a geode. But I didn't usually find it. Well, I don't think I ever found a geode inside any of the rocks I smashed. Oh, but you found some other things, right? That is cool. However, kids, if you're going to break a rock...

Please do get an adult. Good point. Some geodes are really hard. Remember we talked about hardness? Some can be really hard that you hit it and you hit it and you hit it and it doesn't break and you need an adult to come help you. And when you're breaking rocks, especially if you don't know how hard the rock is, you should wear protective eyewear so that you don't hurt your eyes. Wear protective eyewear, wear gloves.

Put the rocks in a sock maybe so that it doesn't scatter splinters all over. Just be careful. Our last question comes from Monroe. I was born in New York City and I moved to Los Angeles, California.

I'm six years old, and my question is, why do some rocks have gems in them and other rocks don't? Why do some rocks have gems in them and other rocks don't? So we've talked about geodes, but there are also rocks, like a rock that I used to look for a lot in Maine, that had little flecks of garnet inside it. And garnet is a gemstone. It wasn't a big rock.

honking garnet piece, but it was a rock that had gemstones in it. So why do some rocks have gems and some don't? The way I want to answer this question is some rocks have gems in them because rocks are like cookies. There are so many types of rocks and like so many types of cookies, sometimes they have goodies in them. It may be chocolate chips, it may be M&M's, it may be nuts,

Whatever Mother Nature chooses to put in these rocks can create germs. Germs are minerals that have bright colors, beautiful crystal forms, shiny. So they have characteristics that we enjoy. So if you see a rock that has these minerals, then that rock has germs.

Sometimes an igneous rock would have minerals that have gemstone in them. Sometimes you have a sedimentary rock. Sometimes you have a metamorphic rock. So it really is not one particular type of rock. It's just the kind of minerals that makes that particular type of rock. And it depends on what was in the yummy soup, what type of particles or bits came together.

Or how the rocks were stretched and bent to put those germs together. So it's not one particular type of rock. And also, let me just say something. I think germs depend on who is looking at them. So sometimes if you see a rock that has really beautiful crystals, minerals that you like and you enjoy, that is your germ. It's precious to you.

There are some that we all agree because we all can see that they are shiny and that they look beautiful, but there are some that are very unique to each person. And that is okay, too. A gem in a rock might not look as shiny as you'd see it in a piece of jewelry, right? Because it's not been smoothed and polished. So it's not necessarily going to blind you when it catches the sunlight in the way a piece of jewelry might. It's like...

Dressing up right, you have to put some effort into it to make it look really nice.

So you start off just being in your PJs and then by the end of the morning, you're so dressed up and you look so flashy and beautiful and handsome, however you want to look. That's the same things that we have to do with gems. We have to take them and polish them up, fire them, bring out their shininess and their smoothness, help them reflect light better so that we can appreciate them.

Well, so now every day when I get up and I brush my teeth and I put on my clothes and put on my glasses, I'm going to walk around and say, now I am a gem. Yes, indeed. That's what I want everybody to think about. When you get up and you get ready for the day, think of yourself as a gem. You're a gem to the world. And all of you are gems, too.

Thank you so much to Hendrata Ali for answering all of our many rock questions. She's a professor of earth science at Fort Hayes State University in Kansas. Oh, and before we go, Hendrata taught us how we can make diamonds. First, take something with carbon in it. Bury it deep inside the earth so there's no oxygen. Then put enough heat and pressure on the substance to make it become soft.

Third, Hendrata told us, make sure there's not too much heat to melt it all together. And over time, with all that pressure, you might start making graphite. Remember, graphite is also made of carbon. It's the softer mineral that's in our pencil tips. But if there's enough heat and pressure over time, you'll get a diamond. All right, I think you've probably guessed that you can't actually do that yourself. That is a naturally occurring process that happened once

of years ago to make the diamonds that we have today in our tools and in our jewelry. There are people who are making synthetic or artificial diamonds, but all of those natural diamonds came through that long ago and deeply involved process. Still, it's kind of neat to think about how diamonds are made in that simple way and maybe to imagine we could make them ourselves. Okay, that's it for today. If you have a question about anything,

Have an adult record it for you. Tell us your first name, where you live, and how old you are, and then what your question is. You can email your question to questions at butwhykids.org. Our show is produced by Melody Beaudet and me, Jane Lindholm, at Vermont Public Radio. Our theme music is by Luke Reynolds. We're distributed by PRX. We'll be back in two weeks with an all-new episode. Until then, stay curious.

From PR.