Neighborhood Rocks Search this Site

Brown Chert ("CHURT")

		Chert is one of the most common rocks in our neighborhood. To learn more about brown chert, scroll farther down this page.
You can buy 50-pound bags of brown chert at hardware and garden stores.



This paving stone made of brown chert embedded in concrete.	Brown chert gravel fills in the narrow space between sidewalk and fence.

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

	This variety of chert is usually brown or creamy white, and it sometimes looks smooth and waxy. (Chert also comes in white 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.

Brown quartzite pebbles:

	The outside of these pebbles is very rounded and smooth.
	Broken edges look glassy, not waxy.

	Look for fossils like corals (yellow arrow) and lacy bryozoans (blue arrow). Here's a close-up of the lacy bryozoans:

	Look for broken edges that are sharp, and broken sides that show a pattern of curved ridges (blue arrow). Because chert breaks in this way, prehistoric Indians used it to make tools like knives and spear points.

	Look for holes filled with quartz crystals (upper arrow), and patches of thinly layered chert that almost look like agate (lower arrow).

Because it's sometimes sold as "Meramec" stone,
we suspect that brown chert comes from the Meramec
River area in Missouri and Arkansas.

Brown chert probably formed within limestone rocks,
perhaps before the limestone was completely
hardened into rock.

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

We've seen 50-pound bags of brown chert labeled "Meramec" (at Home Depot and Frank's Nursery and Crafts) and "River Pebbles" (at Walmart).

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 Web site describes the many types of chert found in Illinois.
(This site also has lots of pop-up ads.):
< 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 Web site:
< 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.