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Scoria (a type of Basalt)

		Basalt is a dark-colored rock that formed as lava cooled and hardened. Scoria is a type of basalt that's full of bubble holes. The bubbles formed as the lava was blasted out of a volcano, and were trapped as the lava cooled and hardened. The scoria in our Chicago-area neighborhood came all the way from Idaho. To learn more about scoria, scroll farther down this page.
Black-colored scoria

Red-colored scoria

	How to recognize scoria
	Other rocks that look like scoria
	Special things to look for
	Where scoria came from
	How scoria formed
	Other names for scoria
	Links to Web sites about scoria, lava, and volcanoes

How to recognize scoria

	Scoria can be black, dark gray, or red.
	Scoria is full of holes, and the holes are often uniform in size and shape.
	Despite all the holes, scoria doesn't float in water.

Other rocks that look like scoria

Slag:

	Compared with natural scoria, slag is often more glassy looking, and there are lots of different colors on some pieces.
	The bubble holes in slag are less regular in size and shape.

Pumice:

	Pumice is usually tan or light gray, and is often more glassy looking than scoria.
	Dry pumice feels very light weight for a rock -- it often floats in water.
	Pumice often looks more delicate than scoria, because the bubbles holes are often smaller and the rock walls between the holes are thinner and more transparent.

Special things to look for

	Some bags of scoria include more solid chunks of basalt.

	Look really close, and you may see bubble holes with interesting shapes. Some of these holes looks like they were stretched out before they hardened.

The scoria in our Chicago-area neighborhood
came all the way from Idaho.

We're wondering if our scoria was quarried
from relatively young volcanoes, like the ones
that made Craters of the Moon National Monument,
or more ancient lava flows, like the Columbia
River flood basalts. We'll update this Web page
once we find out.

How scoria formed

Scoria formed as lava exploded out of a volcano.
Gas bubbles formed inside the lava, and were
trapped as the lava cooled and hardened into rock.

Other names for scoria

We use the scientific name "scoria" for this rock,
but it is also known by other names:

	We've seen 50-pound bags of scoria gravel labeled "volcanic rock" and "crater rock."
	Some people in our neighborhood call it "lava rock."

Here are some ways to classify scoria (by grouping it with similar types of rocks):

	Scoria is a variety of basalt.
	Scoria is an igneous rock, because it formed from melted rock.
	Scoria is an extrusive igneous rock, because it formed from lava "extruded" onto the surface of the Earth.

Links to Web sites about scoria, lava, and volcanoes

Here's a Franklin Institute Web page about scoria. Be sure to
follow the "See how igneous rocks are formed" link at the
bottom of the page:
< http://www.fi.edu/fellows/payton/rocks/expert/scoria.htm >

Here's a United States Geological Survey article about
scoria:
< http://volcanoes.usgs.gov/Products/Pglossary/scoria.html >

The VolcanoWorld Website has a good article about
Craters of the Moon National Park in Idaho (written for
older kids and adults.) It includes pictures of basalt lava
flows:
< http://volcano.und.nodak.edu/vwdocs/volc_images/north_america/craters_of_the_moon.html >

VolcanoWorld also has a good article about the Snake
River Plain and Columbia River flood basalts in Idaho
and nearby states:
< http://volcano.und.nodak.edu/vwdocs/volc_images/north_america/crb.html >

VolcanoWorld has lots of information and activities for kids:
< http://volcano.und.nodak.edu/vwdocs/kids/kids.html >