Neighborhood Rocks Search this Site

Slag (human-made "lava" rock)

		Slag is lava-like stuff made by people. We find slag whenever we dig in the soil near our home. We find lots of slag whenever they tear up old sidewalks or streets. Like lava, slag formed from melted rock. Some slag was made in super-hot coal-burning furnaces in steel mills, power plants, and steam locomotives. Other slag formed in old-time home furnaces, which used to burn coal. (Now most home furnaces burn natural gas or fuel oil.) To learn more about slag, scroll farther down this page.
Slag found under a sidewalk.

Aaron collecting slag under a torn-up sidewalk.

	How to recognize slag
	Other rocks that look like slag
	Special things to look for
	Where slag came from
	How slag formed
	Other names for slag
	Links to Websites about slag

How to recognize slag

	Slag can be black, gray, whitish, or reddish -- and some spots may shine with the colors of the rainbow.
	Some pieces of slag have rounded bubble holes, but these are often mixed with crumbly and smooth glassy spots
	Some pieces of slag fizz in acid or vinegar.

Other rocks that look like slag

Scoria:

	Scoria is often less glassy looking than slag.
	Scoria is usually more uniform in color.
	The bubble holes in scoria are usually more rounded and regular in shape.

Special things to look for

Where slag came from

Most slag around here was shipped in from
steel mills, power plants, or other factories
that burned coal. Some slag was probably
cleaned out of people home furnaces, which
used to burn coal.

How slag formed

Most of the slag that we find around here probably
formed from melted rock made by super-hot,
coal-burning furnaces in places like steel mills.

Other names for slag

	Crumbly pieces of slag are sometimes called "cinder."
	Slag that formed in old-time coal-burning furnaces is sometimes called "clinker." Drop a piece on the sidewalk, and you'll hear why!
	Kids in our neighborhood sometimes call slag "meteorites." When you think about it, slag really does look like pieces of meteorite that you find in museums and books.

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

	Because slag formed from lava-like melted rock, it's sort of like an igneous rock -- but because humans made the melt, it's not a true igneous rock.
	So, we made up a new classification for slag: We call it a pseudo-igneous rock (pronounced "SUE-doe ig-NEE-us). That means "fake igneous rock."

Links to Websites about scoria, lava, and volcanoes

Encyclopaedia Britannica has an article about slag:
< http://www.britannica.com/eb/article?eu=69911&tocid=0 >

Find

Collect

Name

Play

Link

Home

Neighborhood Rocks is part of the Salt the Sandbox Web.
For more information visit the Salt the Sandbox home page.

This page was created on October 9, 2001, and it was last updated on July 27, 2002.