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Practicals

Volcano in a Beaker
AKA: Igneous Rocks

Summary

A demonstration to show how igneous rocks form using sand and wax in a beaker.

Operation

This practical is best done as a demonstration. A flexcam connected to a projector or television allows the whole group to see the volcano close up.

Equipment required (per set)

  • Beaker (250ml)
  • Clean sand
  • Red wax
  • Bunsen burner
  • Tripod
  • Heatproof ma
  • Gauze
  • Safety screen
The sand first has to be washed to remove any particles that may form a scum or float to the surface. It is easily washed by rinsing with flowing water and removing floating particles.

The red wax must be melted in the beaker to a level of about 1cm. Do his gradually and carefully ensuring the wax does not boil. Red wax can be found in some candles but some cheaper candles are in fact white wax with a red coating. The wax has to be red all the way through for this to work effectively.

When the wax has set solid, cover the surface in about 1cm of clean sand. Then fill the beaker with water until it is about three quarters full. Ensure the sand layer is level. Now your volcano is ready to heat.

The water represents the upper crust of the Earth, whereas the sand and wax represent the lower crust and upper mantle respectively.

The beaker should be heated from below ensuring there is a safety screen separating the equipment from the class.

As the wax melts, it becomes less dense (like in a lava lamp) and rises. This 'magma' breaks through the lower crust and some will 'volcano' up to the surface mimicking a volcano.

Some of the wax will cool quickly in the cold water and form 'intrusive igneous rocks'

The demonstration allows teachers to explain several key elements of tectonics, earth structure and volcano activity. It is relatively clean and simple to set up. Once the equipment is returned, the wax layer may be solid and floating on the surface of the water which is easily removed. If the wax is mixed with the sand and forming blobs, it may be reheated until the elements are separated which makes for an easier disassembly.

The clean sand can be reused as can the wax.

Safety

 CautionUse a safety screen.

Wear eye protection.

The contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.