Crystal models made of marbles

Class practical

Students pile marbles into a cardboard tray and so find a convenient way of packing them together.

Apparatus and Materials

For each student group

• Marbles, 1.5cm diameter, 55
• Card, thin, approx 13cm square

Health & Safety and Technical Notes

A lively class will need careful instruction to avoid spilling marbles all over the floor.

Read our standard health & safety guidance

Improvise the trays on which the marbles are to be stacked from the sheets of card. These are marked with lines about 2 cm in from the edges as shown in the diagram. Most important is that when the edges are folded up along these lines, a row of 5 of your marbles can snugly but comfortably fit between them. Make cuts as shown, and fold and staple the edges to form a square tray.

The base of the tray must hold a layer of 25 marbles. Marbles tend to vary a bit in size.

Procedure

Students pour in marbles to form a layer of 25 marbles. On top of this they add layers of 16, 9, 4 and 1 marbles to form a pyramid.

Teaching Notes

• Students should notice the shape of the model crystal they are building and the angles between its faces. (They may need reminding that their model is of a tiny number of particles/atoms compared with that making up a real crystal.)
• You could ask students if they can identify real crystals with the same shape or angles between faces as their model. Alum would be a good example.
• You can draw students' attention to the fact that even if a marble is (carefully!) removed, the shape of the crystal remains.

This experiment was safety-tested in September 2004