ShmoopTube

00:13

Growing up, we tend to classify rocks not by their type, but by their purpose… [Woman holding rocks]

00:18

Flat rocks are good for skipping on the lake...

00:20

Small rocks are good for waking up your friends in the middle of the night... [Rock smashes into window]

00:23

And giant rocks are perfect for showing off how strong you are.

00:26

Or sometimes…how not-so-strong you are. But in the world of science, rocks tend to [Man falls to ground holding giant rock]

00:31

be classified into three different types:

00:33

Igneous, metamorphic, and sedimentary – and all three have their own specific properties, as well as uses.

00:39

Igneous rocks are rocks that were once, well, not so rocky.

00:43

Kind of like music, before Elvis hit the scene. [Elvis singing on stage]

00:45

But back to the rocks…what we mean by "not so rocky" is that igneous rocks weren't always rocks.

00:51

They actually start as liquefied rock, bubbling deep down below the surface of the planet, [Lava bubbling]

00:56

where they're melted by the Earth's core.

00:58

Once the molten rock comes up to the surface and gets some fresh air, it rapidly cools off. [Molten rock appears from mountain]

01:03

And when it does, it turns back into solid rock.

01:05

Examples of igneous rock include granite, basalt and obsidian.

01:09

And igneous rocks tend to be pretty darn cool looking, which is why they're often used by [Kitchen appears]

01:13

interior designers to make things like countertops, backsplashes, sinks, floors, and tabletops.

01:18

We heard some designers wanted to use them for mattresses…kinda glad that never caught on. [Girl sleeping on rock mattress]

01:22

Next, we've got metamorphic rocks.

01:24

These rocks are also created by heat, but they skipped that whole messy "liquefied" phase. [Coop discussing metamorphic rocks]

01:29

When a rock is exposed to extreme heat – but not enough heat to straight-up melt it – it

01:33

can still be affected by it, and transform into a new, metamorphic type of rock. [Rock goes into super heat machine]

01:37

Kind of like when Pokémon evolve, but…way less interesting to watch.

01:41

Because so much heat is needed to make them, metamorphic rocks are usually found below [Metamorphic rocks under earths surface]

01:45

the earth's surface or near volcanoes. Examples include jade, marble and slate.

01:50

Metamorphic rocks have been used in art, sculpture, and construction throughout the history of

01:54

humanity – from the Ancient Greeks carving marble statues and columns to roofers using [Ancient greek statue appears]

01:58

slate tiles today. Then we've got sedimentary rocks, which are

02:02

formed on the surface of the earth when different rock sediments are fused together over time. [Dino discussing sedimentary rocks]

02:06

Sedimentary rock is the most common type of rock to be found on the earth's surface, and

02:10

include sandstone, amber, and limestone, which does not taste like limes…

02:14

Trust us on this one. [Girl at restaurant table with menu]

02:15

Since sedimentary rocks are so common and plentiful, we regularly use them in construction

02:19

– if something is made from cement, sand, or gravel, well then it's made from sedimentary rocks.

02:24

Take one look at a city and you're basically just looking at rearranged sedimentary rocks.

02:28

And you thought we were long past the stone age. [Cave man in New York]

02:31

Clearly, rocks are essential to human civilization – without them, we'd be living in, well, dirt.

02:36

But rocks aren't exactly…perfect.

02:38

One of its biggest drawbacks is that natural weather like wind and rain can take its toll [Rock in street being rained on]

02:42

on rock, eventually eroding and weathering it.

02:45

Buildings can erode...

02:46

Ancient art can deteriorate...

02:48

And even that gorgeous marble sink might eventually erode from use – though you might need to [Marble sink eroding from water]

02:52

give it a few thousand years.

02:54

But hey – considering the Earth so generously offered us all of this amazing rock for free,

02:58

we probably shouldn't be complaining.

Full Transcript