Posted by: tpsciencefun | October 14, 2013

Making “Mock” Sedimentary Rocks

Recipe from the FOSS Earth Materials Fourth Grade Science Kit.

FOSS Earth Materials Module
© The Regents of the University of California
Can be duplicated for classroom or workshop use.

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250 ml (1 cup) white flour

125 ml (1/2 cup) salt

10 ml (2 tsp.) alum

125 ml (1/2 cup) water

5 drops red food coloring

5 drops blue food coloring

3 drops yellow food coloring

250 ml (1 cup) coarse sand

125 ml (1/2 cup) gravel, 2 colors

30 ml (1/8 cup) oyster-shell pieces


• Bowl or large zip bag

• Stirring spoon

• Measuring utensils

• Tray, cookie sheet, or plates

• Paper towels

(Makes 18 5-cm rocks)

1. Mix the flour, salt, and alum in the bowl or large
zip bag.
2. Add the food coloring to the 1/2 cup of water.
3. Add the colored water to the flour mixture. Knead
the mixture until it is uniform in color and texture
and no longer sticks to the side of the bag or bowl.
(Add a little more water if the dough is crumbly.)
4. Add the sand and the gravel to the mixture and
knead until it is well mixed.
5. Divide the mixture into 18 balls, varying in size.
Hold a rock ball in the palm of your hand, and
with your thumb make a small hole in the center.
Place 10–12 pieces of oyster shell in the hole and
mold the dough around them.
6. Work the ball of dough in your hands, smoothing
its surface. Flatten the rock so that it is 1– 2 cm
thick. (Thinner rocks dry more quickly.) Create a
set of rocks that vary in size and shape by making
each rock a little different.
7. Put the rocks on a plate or tray. Make sure the
rocks do not touch each other. Place them in a
warm area to dry. Turn them each day so they
will dry thoroughly. It takes them about a week
to dry, depending on the humidity.
NOTE: Do not put rocks in a microwave or electric
oven; they get much too hard. Drying time can be
reduced by placing the rocks in a traditional gas
oven. Don’t turn on the oven. The heat from the
pilot light will dry the rocks in 24 hours.
8. Use a paper towel to wipe the sand and gravel
pieces from the utensils so that the solid materials
do not go down the drain.

Break one of the rocks after 6 days to make sure
they are thoroughly dry and hard, but not so hard
that they can’t be broken in half by hand and
taken apart with the nail (the geologist’s pick).



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