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White Chert ("CHURT")

		Chert is one of the most common rocks in our neighborhood. It comes in many colors: white, creamy, tan, and brown are the most common kinds. We sometimes find white chert mixed with the dolostone gravel used to make driveways and roads in our area. To learn more about white chert, scroll farther down this page.
Here's some chert gravel, dug out of a quarry near our home.

This truck is dumping a load of dolostone gravel on our street. We found lots of white chert mixed with this rock.

	How to recognize white chert
	Other rocks that look like white chert
	Special things to look for
	Where white chert came from
	How white chert formed
	Other names for white chert
	Links to Web sites about white chert

	This variety of chert is white, and it may look either chalky or very smooth. (Chert also comes in brown and other colors.)
	Freshly broken edges may be scalloped or sharp.
	You can't scratch chert with a nail or knife. (See more about the scratch test.)
	Chert is made mostly of extremely tiny crystals of the mineral, quartz.

Dolostone:

	Dolostone is usually light gray, not white.
	Dolostone is softer -- a nail scratches dolostone, but not chert.
	Chert often breaks to form sharp or scalloped edges, but dolostone usually does not.

Marble:

	Marble is often sparkly white in the sun, but white chert looks chalky, smooth, or waxy.
	Marble is softer -- a nail scratches marble, but not chert.
	Chert often breaks to form sharp or scalloped edges, but marble does not.

If you look closely, you may find things like these.

	You may find both white and gray chert pieces in dolostone gravels.

	Look for fools' gold (pyrite or marcasite) crystals. The dark specks on these rocks look like brassy metal under our Intel Play QX3 computer microscope.

	The white chert that we found around here came from a dolostone quarry, like to one in this picture.
Dolostone quarry near Brookfield, Illinois.

The chert may have formed inside deposits
of limy mud that eventually became dolostone

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

	Chert is a sedimentary rock.
	Chert is sometimes classified as a chemical sedimentary rock, because it often forms when limestone or dolostone is chemically changed.

This article describes the some of the types of chert
found in Illinois:
< http://www.chert.cjb.net/ >

If you want to learn how to make stone tools out of
chert, try The Knappers Corner:
< http://www.eskimo.com/~knapper/index.html >

Twenty years ago, John White tried to teach me to knap chert.
(I wasn't very good at it!) Here's his Website:
< http://www.ob1.com/iae/Supporters/Ancient/Lifeways.htm >

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This page was created on May 2, 2001, and it was last updated on July 27, 2002.