Sedimentary crackles

Geology is a lot easier to digest when chocolate is involved.


Younger readers should have an adult present when using the stove.

You will need

  • one cup of icing sugar
  • one cup of coconut
  • four cups of Rice Bubbles
  • 250 g of copha
  • three heaped tbsps of cocoa
  • stove
  • patty pans
  • sauce pan
  • wooden spoon
  • mixing bowl
  • sifter

What to do

  1. Sift together the icing sugar and cocoa and then add the coconut.
  2. Melt copha in a saucepan and when just melted add the dry ingredients and mix together.
  3. Spoon into patty pans and refrigerate.

What's happening

You have just made a model of sandstone, which is a sedimentary rock.

Sandstone forms in places where there was once a large amount of sand such as a river, lake, sea or desert. Little by little the layers of sand build on top of each other. This puts pressure on the lower layers. The weight of all of the layers pushes down on the lower layers. The rock is stuck together with the minerals that fall between the grains of sand. The most common materials that stick the grains of sand together are silica and calcium carbonate. This takes millions of years to happen. During that time, the ocean, lake, or other body of water dries up. This makes the sedimentary layer that used to be under water, become a surface layer.

In your model of sedimentary rock the Rice Bubbles are the grains of sand, the chocolate mixture is the minerals that stick the grains of sand together and the coconut is the little bits and pieces of animal and plant matter that can get caught in the sedimentary rock.


Have an enquiry about this page?

Contact us

Subscribe for more science activities

Our newsletter Science by Email gives you science news, fun activities and a quiz every week.

Subscribe to Science by Email