Wednesday, 28 October 2015

Science: How to make a Geode

So this is how to make your own geode!  

Ok, it's not a real geode but this simple but fun experiment can help kids understand they are formed. To be honest, how geodes are formed is still a phenomena but scientists have a couple of theories one of these theories is lava!

First here's how to make your own geode...

You will need:
  • Clean empty egg shells
  • A jug
  • Water
  • Epsom Salts
  • Food colouring
  • A pipette

Place your empty clean egg in an old egg.  When cracking an egg for this project I try just to crack the top of the egg.


Add 20ml of epsom salts to 60ml of hot water and stir until it's completely dissolved.  If there are no grains of slt remaining add another 5ml and stir until it dissolves.  Keep adding 5ml of Epsom salts until the water is saturated with the salt - that means there will be some Epsom salt that can't dissolve int the water because the water is completely saturated in the Epsom salts. 


Pour the solution into your empty egg shell. 


Using a Pipette add 2ml of food colouring of your choice to the egg, gently.  After a day, observe what is happening to the solution - there should be crystals forming.  Add another 2ml of the same colour or a different colour to your solution.  Leave in a warm place.


On the second day observe what is happening your solution.  

Check on your geode everyday until the solution has completely changed into crystals.

Other things you can try...

Different chemicals!

Try: Copper Sulphate, or Boric Acid.  You will notice that different chemicals have different crystal structures.  This is important to observe too.

What is a geode?

A geode is a spherical (round) rock that is filled with crystals.  Most commonly quartz. Quartz is a silicate, silicates are the most common mineral, 90 percent of the earths crust is made up of silicates.  

The colour of the crystals can depend on the mix of minerals - magnesium in quartz creates amethyst, where as magnesium in Calcite creates a pink crystal.

Heat can also change the colour of a geode's crystals - for example is a quartz geode is heated it's colour can change to a more yellow colour.

How are Geodes formed?

Scientists believe that some geodes are formed out of molten lava rocks.  After the molten rocks cool a chemical reaction occurs that creates gasses.  When these gasses dissolve they turn into bubbles.

When these bubbles harden, cool further, the bubbles turn into cavities - holes.

Scientists believe that there are two possible ways that the geodes form crystals.  There are:
  • The minerals were trapped in the bubbles as hot water passed through the lava
  • They were deposited much later as mineral ground water

These Crystals time time to form, as the water evaporates , the minerals are left behind and as they are they create pretty crystals.

If you like you can try my underwater volcano experiment to observe how lava, the gases below and the water above work to create these bubbles of  molten rock. Just click on the photo below...


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