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Neighborhood Rocks                                     Search this Site

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

How to recognize white chert

bulletThis variety of chert is white, and it may look either chalky or very smooth.  (Chert also comes in brown 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 white chert

Dolostone:  
bulletDolostone is usually light gray, not white.
bulletDolostone is softer -- a nail scratches dolostone, but not chert.
bulletChert often breaks to form sharp or scalloped edges, but dolostone usually does not.
  
Marble 
bulletMarble is often sparkly white in the sun, but white chert looks chalky, smooth, or waxy.
bulletMarble is softer -- a nail scratches marble, but not chert.
bulletChert often breaks to form sharp or scalloped edges, but marble does not.

 

   

Special things to look for

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.
             

   

Where white chert came from

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

 

 

Dolostone quarry near Brookfield, Illinois.

  

How chert formed

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

 

Other names for white chert

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 Websites about chert

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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Copyright 2001-2002 Eric D. Gyllenhaal                                         Search this Site
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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.