Science corner

19th September 2003 at 01:00
Sophie Duncan experiments with rocks and chocs.

What are these? They grow on trees. They have been used as currency in Central America. They were used to make a bitter sweet drink with chillies.

Europeans replaced the chilli with sugar to create a drink few could afford. They are cacao beans, used initially in Europe to make chocolate drinks.

In 1828, a Dutch inventor called Hendrik Van Houten created a method for making the solid that we know today.

Chocolate is a great motivator for learning.

In this investigation, your students are geologists who have travelled to another planet and have collected samples of rock (chocolate). By observing the samples and noting their structure the teams work out how the different rocks are formed. A clue sheet might help.

"Rocky road chocolate" provides the "sample" of a chondritic meteorite. It has a lumpy texture, and contains round pieces called chondrules. To make rocky road chocolate, line a baking sheet with aluminium foil and pour in 200g of melted chocolate. Add 100g of marshmallows and stir until they are coated in chocolate. Pour 200g of melted chocolate on top and place in a fridge until cold. Cut the chocolate into cubes.

Brownies that have been made with chocolate drops and glace cherries have a structure like igneous rock. Igneous rock forms from magma from a volcano.

As it cools, crystals form in the rock - the larger the crystals the slower the cooling process. For a rock that cooled quickly, try mint crisp chocolate.

When magma rises from the earth's surface it releases bubbles of gas. When released quickly, an explosive eruption occurs. The bubbles are trapped in the rock, making it look like a sponge. Chocolate with a honeycomb centre replicates this well.

Meteorites made of iron have a uniform dense structure much like solid chocolate. Other meteorites form a fusion crust as they get heated entering the Earth's atmosphere. This can be shown with a chocolate bar with a uniform filling and chocolate covering (for example, a Milky Way).

The experiments can be found in The Little Book of Experiments, sent to primary schools by Planet-Science, and on

Sophie Duncan is project manager for science at the

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