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.
bulletHow to recognize chert
bulletOther rocks that look like chert
bulletSpecial things to look for
bulletWhere brown chert came from
bulletHow brown chert formed
bulletOther names for brown chert
bulletLinks to Web sites about chert 

How to recognize chert

bulletThis variety of chert is usually brown or creamy white, and it sometimes looks smooth and waxy.  (Chert also comes in white and other colors.)
bulletFreshly broken edges may be scalloped or sharp.
bulletYou can't scratch chert with a nail or knife.  (See more about the scratch test.)
bulletChert is made mostly of extremely tiny crystals of the mineral, quartz.

Other rocks that look like brown chert

Brown quartzite pebbles:
bulletThe outside of these pebbles is very rounded and smooth.
bulletBroken edges look glassy, not waxy.

Special things to look for

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).

Where brown chert came from

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

How brown chert formed

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


Other names for brown chert

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

bulletWe'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):
bulletChert is a sedimentary rock.
bulletChert is sometimes classified as a chemical sedimentary rock, because it often forms when limestone or dolostone is chemically changed.


Links to Web sites about chert

This Web site describes the many types of chert found in Illinois.
(This site also has lots of pop-up ads.):
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If you want to learn how to make stone tools out of chert, try 
The Knappers Corner:
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Twenty years ago, John White tried to teach me to knap chert.
(I wasn't very good at it!)  Here's his Web site:
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Copyright 2001-2002 Eric D. Gyllenhaal                                         Search this Site

Neighborhood Rocks is part of the Salt the Sandbox Web. 
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This page was created on May 2, 2001, and it was last updated on July 27, 2002.