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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.

	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 >

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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.