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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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This page was created on March 12, 2001, and it was last updated on July 27, 2002.