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Neighborhood Rocks                                     Search this Site

Mock Rock

Before During After

Mock rock is pretend rock (kind of like play dough,
but with sand in it).  We make mock rock, bury stuff 
in it -- polished rocks, fossils, whatever -- then dig 
out the stuff.

Recipe.  We adapted this recipe for mock rock from 
one used at the University of Kansas Natural History 
Museum.  To make a couple of tennis ball-sized 
chunks of mock sandstone rock, we used these 
ingredients:

    1 cup flour
    1/2 cup salt
    2 teaspoons alum
    1 cup coarse sand
    1/2 cup water
    5 drops red food color
    3 drops blue food color
    3 drops yellow food color

The alum is a preservative to prevent mold.  If we 
add more sand, the mock rock is easier to chip.  

Mix.  First, we mixed the dry ingredients in a bowl.  
Then we added the food coloring to the water.  We 
poured some water into the dry ingredients and started 
kneading the "rock dough" by hand.  Then we slowly 
added more water until it felt like play dough. 

Add rocks.  We wrapped pieces of the dough around 
polished rocks, smoothed out the "rocks," then set them 
on cookie pans to dry.  (We also could have added fossils, 
coins, or anything else that's hard and water-proof).  

Dry.  It took a week for larger pieces to dry all the way 
through.   We turned the rocks every day so they would dry 
evenly.  (In an experiment, we tried to dry rocks faster by 
baking them in an oven set at less than 200 F.  After a few 
hours, the rocks had very hard outer crusts but were still 
kind of mushy inside.)

Dig.  To dig out the polished rocks, we soaked our mock 
rocks in water for a minute or two.  Then we used our 
fingers to break up the rock and large nails to scrape 
off extra mock rock.  (We had blunted the nail points
with a file).  Once the polished rocks were out of the 
mock rock, we soaked them in soapy water for a 
few minutes and then scrubbed them with a toothbrush.

 


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Copyright 2001 Eric D. Gyllenhaal                                             Search this Site
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This page was created on March 12, 2001, and it was last updated on July 27, 2002.