JOAN CARTAN-HANSEN, HOST: Geologists can tell a lot about the Earth by looking at the rocks and minerals found in an area.

Let's visit the Willow Creek Jasper mine to see what the rocks called thunder eggs can tell us about the earth's history.

[MUSIC] CARTAN-HANSEN: This is the Willow Creek Jasper mine in Idaho.

STEVE SCHAPS, RETIRED GEOPHYSICIST: We're inside of an ancient volcano here, which would be about 13 million years old in the Miocene age.

CARTAN-HANSEN: The Miocene is a time, or an epoch, that occurred between 23 to 5 million years ago.

This ancient volcano stayed active for about 1 million years.

SCHAPS: And we're actually in the volcanic vent itself, where there are thunder eggs filled with Jasper embedded in the volcanic ash from a result of all the different eruptions that occurred here.

CARTAN-HANSEN: The volcano, of course, isn't currently active now, so it's a great place to look for jasper.

SCHAPS: "Help!

It's got my arm!"

Jasper is a semi-precious gemstone that's commonly made into jewelry, in the Roman days, back in the old days, they used to use it in water vessels and crowns to show a status symbol of wealth.

CARTAN-HANSEN: Jasper is a type of mineral called quartz.

It's a hard stone that comes in different colors and in spotted, striped, and other patterns.

Today, Jasper is found in rings, earrings and other types of jewelry.

But to get the Jasper, experts have to crack open thunder eggs.

SCHAPS: Thunder Eggs are layered silica deposits that are round, and they look like bowling balls or baseballs.

And the Jasper's inside of the thunder eggs, you have to break the thunder egg open to find the Jasper.

The thunder eggs were originally thought to be gas bubbles inside of the volcanic ash and high temperature fluids fill them up with silica and Jasper.

LARRY RIDLEY, MINE OWNER: Well, the thunder eggs here, or geodes, whatever you want to call 'em, you'll find scattered out through the mine.

One out of 10 has Jasper in it and they run in general, the ones have that have Jasper, are from 2 foot on up to 6, 7, 8 foot.

CARTAN-HANSEN: It takes some effort to crack a thunder egg open to look at what's inside.

If they see Jasper, they chisel away the excess rock until all that's left behind is the beautiful stone.

On this field trip, 9-year-old Jack Wright came to explore the Jasper mine.

JACK: I like to hang out with my dad and go looking for rocks.

CARTAN-HANSEN: This area offers more than just thunder eggs.

Just downwind of the Jasper mine is Willow Creek Canyon.

The canyon is surrounded by rhyolite, a type of volcanic rock.

Rhyolite forms when magma flows from a volcanic vent.

The molten rock cools quickly on the surface.

And that leaves behind rhyolite.

So, geologists look for things like thunder eggs or rhyolite, that tell a story about the different ways a volcano once erupted.

Jack said he wants to be a geologist when he grows up.

And he thinks field trips are important.

JACK: I, think they can learn more about Earth and how Earth was formed and about the crust.

SCHAPS: Geology and geophysics is important for kids to study because the Earth is becoming a more complex place and ground water is a particular interest in a lot of places and to understand the groundwater you have to understand the geology underneath the surface of the earth.

CARTAN-HANSEN: If you want to learn more about the earth check out the Science Trek website.

You'll find it at Science Trek dot org.

[MUSIC] ANNOUNCER: Presentation of Science Trek on Idaho Public Television is made possible through the generous support of the Laura Moore Cunningham Foundation, committed to fulfilling the Moore and Bettis family legacy of building the great state of Idaho.

By the Idaho National Laboratory, mentoring talent and finding solutions for energy and security challenges.

By the Friends of Idaho Public Television and by the Corporation for Public Broadcasting.