[PHONE RINGING]
Hi, it's Doug.
What's the weirdest
rock you've ever found?
Mine is this one.
I just love it.
It's got these green
crystals on it.
Isn't that cool?
I really like this
idea I've heard
that every rock
has a story to tell
if you know how to read it.
Well, this week
someone named Jack
has a question for us
about a rock he found,
and his rock has a
story that I think is
going to really surprise you.
Let's give him a call now.
[PHONE RINGING]
Hi, Doug.
Hi, Jack.
I heard you have
a question for me.
I was wondering, I found this
rock with all these holes in it.
How did it get there?
That's a great question.
Let me show you something.
Here's a close up of the
kind of rock that Jack has.
Why does it have all
these holes in it?
Well, we could just go ask
a rock expert, a geologist.
That's a scientist
who studies rocks.
But how do they know?
How do people figure things out?
Like, how do all the little
holes get in this rock?
The best is if we could
actually see what's
causing the holes to form.
Like, maybe some bird is pecking
on the rock or something.
If we happen to see a bird
doing that, then we would know,
ah, that's why
there's those holes.
But people searched, and
they searched and searched,
and no one saw the holes
being formed in the rock.
They did find a clue,
though, these rocks
are always found near volcanoes.
Well, interesting.
So why would they have
little holes in them?
Scientists carefully
watched volcanoes
to see if they might
notice anything.
Look at this.
This is a close
up of lava flowing
along the side of a volcano.
Do you notice
anything interesting
about this lava flow?
Here, I'll play it one more time
if you want to take a moment
to look more closely.
OK.
You ready?
There's lots of interesting
things to notice.
One thing I noticed
is that there's
all this gray stuff on top.
What is that?
Here, you've got to listen.
Did you hear that?
It sounded like bits of
rock clinking together.
This gray stuff up here is rock.
You might know that
when lava cools off,
as is happening on the
top of the lava flow here,
it hardens into rock.
This stuff used to be
lava that's cooled off
and become rock.
Here's something else I noticed.
This lava is all blocky
and bumpy as it flows.
It turns out, if you look
even closer at this lava,
you see that it's
got bubbles in it.
It's kind of foamy,
similar to the foam
you see on top of a drink.
When that foamy lava cools
and the bubbles burst,
guess what it looks like?
A foamy rock with
lots of holes in it.
The holes are where there
were bubbles in the lava.
It's called pumice,
from an old word
meaning like foam or froth.
Now, all of this is
very interesting.
But I haven't told you the
best part yet about pumice.
Jack, what do you think would
happen if you took a rock
and you dropped it
in a tub of water?
I don't know.
I think it would just
sink to the bottom.
That's true if I use any
rock other than pumice.
But watch what pumice does.
Woah.
See, because pumice
is rock that has
all these little
holes in it, it's
not as dense as most rocks.
It's very lightweight
for its size.
It's so light, in fact,
that it can float on water.
So pumice is a
volcanic rock that
has lots of tiny holes in it.
Scientists have observed lava
when it erupts and found out
that sometimes lava has lots
of little bubbles in it, which
makes it foamy.
As the lava cools
off and becomes rock,
those bubbles burst and become
the little holes you see.
That's what pumice is.
You don't have to
live near a volcano
to find a piece of pumice.
Sometimes pumice
can be purchased,
like at landscaping
stores, where
it's used in people's gardens.
And there's even a skin care
product made out of pumice.
It's good for scrubbing
really rough patches of skin.
If you haven't already
started a rock collection,
pumice can be the first
piece in your rock collection.
Just look for rocks that
have lots of tiny holes.
And if it floats on water,
then you know it's pumice.
Thanks, Jack, for
asking that question.
Now, for next week, I
reached into my question jar
and found three questions
submitted to me that I'm
thinking about answering.
When this video is done playing,
you'll get to vote on one.
You can choose from: How
did donuts get their name?
Why does the planet
Mars look red?
And why is the sky blue?
So submit your vote
when the video's over.
I want to hear from
all of you watching.
Remember, there are
mysteries all around you.
Have fun, and stay curious.
