10
11
ACTIVITY 11 – Growing Crystals in a Rapidly
Cooled Solution
You will need:
• Prepared crystal growing solution (from activity 4 or 5)
• Granite base stone or seed crystal
• Thread
• Pencil
Method:
Place the container with your solution in a bowl of ice cubes and see what happens.
Record your observations.
ACTIVITY 13 – Growing a Large Crystal
Method:
Try growing as large a crystal as
possible by repeatedly immersing a
crystal in a new saturated solution.
ACTIVITY 12 – Growing Crystals in a Slow Cooled Solution
You will need:
• Prepared crystal growing solution (from activity 4 or 5)
• Granite base stone or seed crystal
• Thread
• Pencil
Method:
Try to make the solution
cool slowly. Either place
the container with your
solution somewhere warm,
or place it in an insulated
(e.g. polystyrene) container
with a lid. Record your
observations.
ACTIVITY 14 – Modelling The Structure of a Crystal
Hints & Tips Section
You will need:
• Models of water molecules (cut out from last page of manual)
Method:
A crystal structure consists of atoms or molecules connected in an organised and
repetitive series, packed together as closely as possible. We can illustrate this using the
example of the water molecule, which consists of two hydrogen atoms and one oxygen
atom, better known by the chemical formula H
2
0. The water molecule looks like this:
• If you are having trouble dissolving the crystal growing powder (salt), try adding a small
amount of water to the solution.
• If a large number of small crystals have formed in the base of the jar, remove the seed
pebble. Reheat the solution and stir until all of the crystals have dissolved. Allow to
cool, and put the seed pebble back in the solution.
• If the crystal is not growing, move the solution to a cooler room.
Cut out the models of the water molecules and try to fit them together as closely as
possible. In figure C opposite, the two ends will not hold together, since both have the
same (negative) charge – they would repel. Likewise, in figure D everything is fine at the
top (since there are positive and negative charges together), but not at the bottom (there
are two positive charges close together). Assemble all of the molecules and check that
everything is correct.
Now get someone else to try. In order to get the molecules as closely together as possible,
you will find that they will make a very similar pattern to your own. This is the basis of
crystal formation – for any particular atom or molecule, a particular set of rules must be
followed in order to get them to fit together.
The oxygen atom has two negative charges, and each
hydrogen atom a positive charge – they join together to
form a neutral molecule of water. At room temperature,
the water molecules move around quite freely, so they
are not arranged in any particular way. However, as water
is cooled, the molecules move less and less, until they
reach the freezing point, when the molecules are packed
as closely together as possible. Unfortunately, because
the atoms in the molecules have positive and negative
charges, they will only fit together in a certain way –
remember, like charges repel each other.
Rama Quartz Crystal
Marine Blue Crystal
Molecule of water
Yellow Geode Crystal
Example:
Example:
Example:
