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Neighborhood Rocks                                     Search this Site

Scratch Test 

This simple scratch test helps you tell hard rocks
(like granite, obsidian, and quartzite) from softer 
rocks (like marble, coal, and limestone).

All you need is a shiny new nail (or a knife blade, 
if you are older).  

Using the sharp point of the nail, try to scratch the 
surface of your rock.

Photo of limestone scratched by a nail.  The nail lscratched off a line of white powdered limestone. If the nail digs in and scratches off a line of powdered rock, then the nail is harder than the rock.

In this case, the nail scratched off a line of powdered white limestone.

  
If the nail does not scratch off any powdered rock, then the rock is harder than the nail.

In this case, some of the nail rubbed off on the rock!  This left a line of silvery metal on the white chert.  (This happens pretty often when you try to scratch hard, light-colored rocks.)

  

Geologists have a much more precise scale for 
measuring hardness, called the Moh's hardness
scale.  If you want to learn more about measuring
hardness, go to one of these Websites:
   Go to < http://www.childrensmuseum.org/geomysteries/faqs.html > and click on FAQ #3, "What's a hardness scale?"
   < http://www.afn.org/~jbkramer/rock_moh.html >
   < http://www.luckygemstones.com/mohs.htm >
   < http://www.24carat.co.uk/hardnessmohsscale.html >

Please use your back button to return to the rock 
type you were just reading about.

   


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Copyright 2001-2002 Eric D. Gyllenhaal                                          Search this Site
Webmaster@SaltTheSandbox.org

Neighborhood Rocks is part of the Salt the Sandbox Web. 
For more information visit the Salt the Sandbox home page.

This page was created on September 30, 2001, and it was last updated on July 27, 2002.