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Obsidian ("awb-SID-ee-an") 

Obsidian was once lava from a volcano.  The lava cooled so fast that it formed a glass, instead of crystals. 

So far, we haven't found obsidian just lying around loose in our neighborhood.  However, we bought a 50-pound bag of "Black Obsidian" from a landscape supply store and put it in our garden.

To learn more about obsidian, scroll farther down this page.

  
bulletHow to recognize obsidian
bulletOther rocks that look like obsidian
bulletSpecial things to look for
bulletWhere obsidian came from
bulletHow obsidian formed
bulletOther names for obsidian
bulletLinks to Websites about obsidian
  

How to recognize obsidian

bulletObsidian is mostly black in color.  Surfaces and cracks may be stained tan or brown by weathering.
bulletObsidian looks glassy -- in fact, it's made of naturally formed glass, not crystals.
bulletYou cannot scratch obsidian with a nail or knife.  (See more about the scratch test.)
    

Other rocks that look like obsidian

Coal:
bulletSome coal is black and kind of glassy, like obsidian.
bulletHowever, coal draws a black line if you scrape it on the sidewalk.  (Obsidian draws a white line, or no line at all.)
    

        

Where obsidian came from

There are no volcanoes in Chicago, so the obsidian
we find in our area had to come from somewhere else.
Somebody must have shipped it here by truck or train.
However, so far we haven't found out where it came from.

   

How obsidian formed

Obsidian was once lava from a volcano.  The lava 
cooled so fast that it formed a glass, instead of crystals. 

   

Other names for obsidian

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

bulletWe've bought 50-pound bags of obsidian gravel labeled "Black Obsidian."
bulletMany people call obsidian "volcanic glass."
bulletObsidian sometimes is found as smooth, rounded lumps that some people call "Apache tears."

  

Here are some ways to classify obsidian (by grouping it with similar types of rocks):
bulletObsidian is an igneous rock, because it formed from melted rock.
bulletObsidian is an extrusive igneous rock, because it formed from lava "extruded" onto the surface of the Earth.

   

Links to Websites about obsidian

Here's an Encarta® Concise Encyclopedia article  about obsidian:
   < http://encarta.msn.com/find/Concise.asp?z=1&pg=2&ti=761555559 >

   


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Copyright 2001 Eric D. Gyllenhaal                                              Search this Site
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This page was created on May 2, 2001, and it was last updated on July 27, 2002.